Duramax Head Gasket Replacement

That little hose section behind the fan pulley is the turbo coolant supply. I've replaced mine twice, as well as a bunch of others. Not too complicated or difficult (replaced one in an RV park in less than an hour, once). I prefer the OEM spring clamps, as well, but used screw clamps the last time I replaced the line. I double-clamped it (4 clamps, 2 at each end), and it hasn't leaked since. I reused the OEM spring clamps the first time, and it began weeping rather quickly. As far as I know, mine wasn't/isn't pressurizing the coolant system, such as with a head gasket leak. GM/Duramax surely could have located the soft connection in a better place.

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Originally Posted by DmaxMaverick

That little hose section behind the fan pulley is the turbo coolant supply. I've replaced mine twice, as well as a bunch of others. Not too complicated or difficult (replaced one in an RV park in less than an hour, once). I prefer the OEM spring clamps, as well, but used screw clamps the last time I replaced the line. I double-clamped it (4 clamps, 2 at each end), and it hasn't leaked since. I reused the OEM spring clamps the first time, and it began weeping rather quickly. As far as I know, mine wasn't/isn't pressurizing the coolant system, such as with a head gasket leak. GM/Duramax surely could have located the soft connection in a better place.

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Thanks... Second the notion that GM could have located that hose somewhere with a little better access...

I may try a double screw clamp. The end with the best access is the one oozing.

By the way... And for everyone else, that hose is a 10mm internal dimension coolant hose. It looks like it may be 3/8", but 3/8" is a little small. The hose can be saved by squirting a little coolant on the pipe it is attached to and once the clamps have been loosened, work/move the hose all the way to the left (as you're facing the front of the engine). That should get you enough latitude to remove the coolant pipe that carries coolant to the turbocharger, or replace the hose/clamps if need be.

It's now been a little over 2 years, and the truck has accumulated nearly 13,000 miles since my daughter and I replaced the head gaskets, injectors and injector fuel lines, and resealed the injector cups, resurfaced the head decks and set the valve lash in my 2001 GMC's Duramax 6600. The truck continues to run great, and there has not been a single issue with the head gaskets or any other aspect of the tear-down and re-assembly (other than a minor fuel and coolant leak after the initial startup the first day after the service - that were easily taken care of). None of the head gasket service videos that I've seen online talk about how successful their repairs were over time. A rather important point, considering the "dubious" repair procedures shown in the videos... So, other than to share a little of Montana with you, that's the reason for this update - to talk about the success of the head gasket replacement project that was completed in June of 2021 - done the right way. ;)

https://www.thedieselpageforums.com/...9&d=1692026290

Nearly a hundred miles from home, this pic was snapped on Thursday, August 10th looking north from an overlook situated above the southern end of the beautiful Flathead Lake here in western Montana. Just over the hill and to the left a couple of miles is the small town of Polson, Montana. However, our destination that day was to the right in this photo, on the eastern shore of the lake, to a public facility called Finley Point State Park. We had rented a cabin there for a few days. This trip was possible because the new head gaskets have made the truck a reliable member of the family again.

Flathead lake is among the largest freshwater lakes in the country, being 28 miles long, up to 15 miles wide, and 370 feet deep at its deepest point. The scenic value of this natural wonder is awe inspiring, especially when set against the glacially carved and rugged Mission Mountain Range just off camera to the right. This mountain range reminds me of the glacially carved topography found in Yosemite. Flathead Lake is the result of a very large glacier that had scooped out the lake bottom during the last ice age. This elevated overlook where the truck is sitting is a "terminal moraine" that had been bulldozed into place by that glacier, and which also defines the southern boundary of the Continental Ice Sheet that once covered all of Canada and a northern fraction of what would become the US's lower 48.

We were here, partly, to kayak and to try our hands at fishing. Flathead Lake contains Lake Trout up to 40", good sized Lake Whitefish, Kokanee salmon and several other species (bass, perch, etc). My experience with fishing the lake was pretty limited, but the Zimmerman bait/tackle shop in Ronan, MT set us up with a selection of the right gear, and showed us a chart with water depths describing where each species would be located. This time of year, the bigger fish are all in deeper water, so my daughter and I jigged for Whitefish using artificial lures in about 100-150 feet of water - offshore from Blue Bay. I caught one and had several others on the line. The Whitefish we battled were about 2+ lbs and about 24" in length. Though the limit was a hard-to-imagine 100 per day, we were just catch-release fishing. We found the Whitefish to be hard fighters when using light tackle, and when in a kayak!

We had beautiful weather this trip, and the many cherry orchards around the lake had produced a bountiful crop - there were many open fruit stands all along the roadways. The large Bing cherries were delicious! My daughter even fed a few cherries to a Whitetail doe and fawn just a few feet off the front porch of our rented cabin.

See my signature below for a link to a page that describes our printed and bound Duramax Diesel Service Guide book, which includes a number of service procedures for the Duramax 6600 - including a head gasket replacement project. Do it once, do it right. :)

Jim Bigley

PS - The name "Flathead" came about because of a native tribe that once inhabited this area. Their custom was to bind boards against the heads of younger members of their group, thus modifying their skull shape over time. This was similar to what was practiced by a few native tribes found in both North and South America.

Today, the southern half of Flathead Lake and continuing south for another 50 miles is all within the boundary of the beautiful Flathead Indian Reservation. There is much to see and do within the Reservation, and I encourage those visiting this area to take advantage of the opportunity. Fishing on the reservation requires a reservation permit - available at any license counter here in western Montana or online.

I've known and even worked with a few natives from this area - going back to when I was a teen, and up through the 1990's when I assisted their tribal college to complete the setup and repair of some science tech I was trained for at the University of Montana. We met and talked with a handful of natives during this August 2023 visit. They're still the real deal... This area is a bright spot among Indian reservations. It's beautiful here. You'll be blessed for having visited.

Thanks for sharing, Jim! You definitely live in a beautiful part of the country. I've never been able to visit Montana, but it's on my to-do list.

Casey

I've mentioned here before that Youtube can be a fun place to hang out or learn something you didn't know. However, when it comes to working on your Duramax 6600, a little common sense can go a long way. Back in 2021, I did a search on YT about Duramax 6600 head gasket replacements... I found the most popular video in the list of those I watched to be one where the mechanic was using a horrible technique to prepare the block deck for new gaskets... Here's a screen grab. Yikes!

https://www.thedieselpageforums.com/...1&d=1698432471

The above image would be appropriate if he was grinding off a half inch of body filler - but this is not appropriate prep for new head gaskets. To compound the problem, there is absolutely no attempt to prevent carborundum grinding grit and debris from falling into the lifter galley, onto the piston crowns or into the cooling passages. This is NOT how GM specifies the heads and block decks are to be prepared...

The next image shows what IS recommended by GM - to help prepare the Duramax 6600 head and block deck surfaces.

https://www.thedieselpageforums.com/...2&d=1698433033

This is a 3"x4" steel block that was machined flat on a milling machine. GM recommends using a light oil (I used WD-40) with 600-grit wet/dry paper on the pictured steel block to prepare the cast iron block and aluminum head deck surfaces. I also stuffed the lifter galleys and piston crowns with clean shop rags, and any accumulating oily sludge was prevented from entering the cooling passages. Our Service Guide linked-to below shows how this is done.

The Duramax 6600 head gaskets require a certain smoothness for both the block and head deck surfaces. The design of the head gaskets require this smoothness, and the differing temperature coefficient of expansion between the aluminum heads and cast-iron block demands it. 600-grit provides that smoothness, when used with an absolutely flat steel block.

I had a local fabricator make this block for me, but you could create your own by using a 4" length of 3" steel angle iron. Then make it flat by using a series of coarse/fine grit wet/dry sand paper sheets on glass or a flat counter top. Round the edges before completing the job - so they can't dig into the aluminum heads.

The job of preparing the heads and block isn't that difficult and it goes pretty fast. Jim

I have found if i watch 5 or 6 YT Videos i can find something in one and something else in another. They all seem to leave out a little something that was critical or that made things easier.
But for the price you cant beat it

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Originally Posted by a5150nut

I have found if i watch 5 or 6 YT Videos i can find something in one and something else in another. They all seem to leave out a little something that was critical or that made things easier.
But for the price you cant beat it

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You're right. Though, discernment comes with experience. The video mentioned above was about an hour long - for a project that takes 40+ hours to complete (GM labor rate), so there's a lot left out - a lot of questions unanswered. And, certainly most of the hard parts of the job are left out - the same hard part(s) are left out in each video (I have a theory for why that's so). I watched several other videos for this topic, but found none gave the complete story - a proper story. The video channels all produced content that relied on the viewer to already have a good understanding of auto mechanics in general and Duramax head gasket replacement in particular - when in reality very few actual truck owners have that level of knowledge. These engines and fuel injection systems are complicated - risk of failure is significant, and the video creators never give the viewer a long-term follow-up. What's the price of failure or chronic nagging complications? This is why The Diesel Page has produced Guides that help owners do their own service work, and succeed in that effort.

I know a local Duramax owner who abused his stock Duramax till coolant leaked/poured out in several places (i.e. head gaskets, water pump seal, coolant surge tank overflow, etc). He then hired a local shop to build him an "indestructible" 1000-hp monster - forged pistons, aftermarket rods, big injectors, dual CP3 pumps, twin turbos, etc. It only lasted a couple of months, after the truck owner spent $20K on it. Knowing the story, I blame the shop for the eventual outcome and not properly managing the owner's expectations... An idiot behind the wheel can ruin just about anything. In the end, success sometimes boils down to experience...

I watched a Duramax engine-related video short last evening that was created by a white haired guy in a professional looking shop. The video focused on a Duramax 6600 engine sitting out of the truck with its heads removed. In that video, the white haired guy pointed to the top of a Duramax piston that had been partially melted by what he described as an injector failure. He said this extreme heat had damaged the piston crown and caused the piston to swell in the cylinder, resulting in both piston damage and cylinder damage.

Individual common-rail injectors can fail in ways that cause it to become a fierce blowtorch - a piston melting blowtorch. But, in my opinion, an injector failure wasn't the root of the problem in that video short. What he didn't point out was that other pistons also showed evidence of extreme scorching, produced by excessive fueling, which resulted in EGT temperatures well in excess of 1300 degrees F (maybe even 1500 degrees F). This scorching always produces a distinct and pronounced star pattern on the piston crowns - the melted piston in the video had that scorched star pattern on it. Think about what a Saturn 5 launch pad must have looked like after a moon shot.

My opinion, based on the images, was that the truck owner installed high-flow injectors and ran with a big program that put a lot of fuel into the engine. He then raced or pulled with it, which produced a combustion temperature that the piston(s) couldn't cope with.

The point... I believe the video producer didn't correctly diagnose or describe the problem... I found it curious that the shop owner didn't take the time to show the viewers what the other pistons looked like, and how he characterized their appearance. The video only showed an adjoining cylinder very briefly and incidentally - curious... Truck owners (and video viewers) need to know the whole story of what happened, to help them avoid a problem like that shown in the video. This must have been at least a $10,000 repair.

By way of comparison, here's what a normal Duramax piston crown looks like in a stock daily driver with 140,000 miles on it. There's only the faintest of star pattern on the outer rim, with no star pattern on the bowl.

https://www.thedieselpageforums.com/...1&d=1698862480

In closing, a common-rail injector that fails in a way that allows it to spray unregulated amounts of fuel will likely set a cylinder balance code, will smoke at idle (and above), will run rough and excessive blow-by will huff white smoke out the oil fill pipe with the cap removed - if the engine is run long enough to damage a piston/cyl. I'm not sure how this would affect fuel rail pressures at idle, but I suspect there also may be low rail pressure codes. In other words, a Duramax owner should have ample warning that a serious problem exists - possibly even before damage has been done. An exception to this might be when a Duramax is being used to tow heavy while out on the highway, and the driver simply can't pull over/stop immediately due to safety concerns - he has to keep going. In this situation, it becomes a choice between dollars and sense.

Maybe someone who has experienced this sort of problem with their truck can help fill in the blanks on symptoms. Jim

https://youtube.com/shorts/pySyCI1lR...HunvXKqYnAoKzp

I know that the debate regarding whether to choose head studs or head bolts for a Duramax 6600 will likely never be completely resolved, but here's another voice that addresses the question... ;)

I like Gale Banks. I've met him personally a couple of times, had dinner with him, and we've talked on the phone/email. But... Now, to be fair, the image he uses in this video of block deck bolt thread failure is NOT of a Duramax 6600. I don't know what engine is represented by that pic. You can see in the image in a previous post (of mine) what the block deck actually looks like in a Duramax 6600. The bolt holes are much different, and far less likely to fail like that shown in the Banks video.

Still... I believe Banks would be running studs and selling his own stud kits if he thought studs were either necessary or even just a better choice. Studs are a fairly expensive option. Gale is a businessman...

I agree.
But Gale Banks has not been known for peddling "Goody yum yum" parts simply to make $$$$
Gale has always worked to deliver fixes to real problems......

I have never met Gale buy have used some of his parts....Always top shelf stuff

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Originally Posted by Robyn

I agree.
But Gale Banks has not been known for peddling "Goody yum yum" parts simply to make $$$$
Gale has always worked to deliver fixes to real problems......

I have never met Gale buy have used some of his parts....Always top shelf stuff

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I believe that if Banks thought (or could show that) head studs provided a justifiable benefit, he'd be selling his own - "he is a businessman" after all.

Still... I wish Banks hadn't used a non-Duramax 6600 block deck pic to try to make a point about weak threaded holes in a block deck. That pic wasn't necessary. In my opinion, Banks' opinion/in-house testing is enough to make the point. I trust him.

Studs, however, do have one real advantage over TTY head bolts... Studs are reusable. But... you can buy 3 sets of TTY bolts for the cost of one set of ARP-2000 head studs. This reusable advantage might be important for racers who are inside their engines on a regular basis, but not so much for a grocery getter, commuter, or RV/boat hauler.

As discussed in our Duramax Service Guide, the fire-ring on these head gaskets tend to Brinell (create an impression in the aluminum head decks) over time due to the clamping load of the head fasteners. Both the factory TTY bolts and the ARP studs are torqued to the very same level - 125 ft/lbs. I measured the final torque of the TTY head bolts using a torque wrench during the final TTY angle sweep during installation. And, I installed a set of ARP head studs during another of the Duramax head gasket projects I did a couple of years ago. So... studs aren't being used to add more clamping load, because that would create a deeper fire-ring impression into the aluminum head decks.

Next month will be three years and nearly 16,000 miles since replacing the head gaskets on my 2001 GMC Duramax 6600.

Here's an update...

There has been no coolant loss or abnormal cooling system pressure. The truck has now experienced three winters since the head gasket project - with winter 22/23 seeing as low as -30 degrees F. Once solving the 10mm coolant hose leak a while back, there have been no engine-related issues. Over the past 3 years, the truck was driven on a few longer trips of a 200-300 miles each, some during the winter and some during the summer.

The truck has set a P0700 code (generic all-encompassing Allison trans code) now and then during this time, and even going back to a year or two before the head gasket work. It comes and goes... The transmission has been serviced twice - replacing the fluid and both filters. The most recent trans service was summer 2021. The root problem with the trans code may be related to a contact issue for one of the pins at the transmission's electrical connector. This has been reported by others on the Internet. The code setting hasn't produced a change in how the engine/trans runs or performs. I'll try to get the problem totally resolved this summer. In the meantime... it's a backburner issue. If anyone can add to this P0700 diagnosis, pls let me know.

P0700 is only the TCM requesting the PCM to illuminate the SES lamp, which drops the P0700 in the PCM shell DTC. It is not a error or failure, in itself. If the SES lamp is on, and you have a P0700, you need a scanner/reader capable of reading TCM data to recover the causal trouble code(s). Common "code readers" don't do this. Also, the TCM does not clear the P0700. The PCM simply expires it, if there are no further pending TCM codes, after a specific number of warming or starting cycles, depending on the code class. Transient TCM codes tend to clear themselves very quickly, and can leave behind a P0700 ghost. If possible, check the DTC's before shutting down the session it occurred. Some of them clear at the next restart if the condition is not present, and some of them do not print in history. Speed and pressure codes (slippage) remain for several warming cycles, while most solenoid timing, voltage and temperature errors may not last through 2 restarts if they don't repeat. There is also a trigger for limp mode, but I haven't figured out that one yet. I recall seeing a chart of the code classes and reactions, but can't find one now. It may have been in my Alldata account, but I haven't renewed since they priced me out of their market.

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Originally Posted by DmaxMaverick

P0700 is only the TCM requesting the PCM to illuminate the SES lamp, which drops the P0700 in the PCM shell DTC. It is not a error or failure, in itself. If the SES lamp is on, and you have a P0700, you need a scanner/reader capable of reading TCM data to recover the causal trouble code(s). Common "code readers" don't do this. Also, the TCM does not clear the P0700. The PCM simply expires it, if there are no further pending TCM codes, after a specific number of warming or starting cycles, depending on the code class. Transient TCM codes tend to clear themselves very quickly, and can leave behind a P0700 ghost. If possible, check the DTC's before shutting down the session it occurred. Some of them clear at the next restart if the condition is not present, and some of them do not print in history. Speed and pressure codes (slippage) remain for several warming cycles, while most solenoid timing, voltage and temperature errors may not last through 2 restarts if they don't repeat. There is also a trigger for limp mode, but I haven't figured out that one yet. I recall seeing a chart of the code classes and reactions, but can't find one now. It may have been in my Alldata account, but I haven't renewed since they priced me out of their market.

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Thanks Greg. I had a local friend (and mechanics garage owner) attempt to pull the codes using his commercial Snap-On code reader. He couldn't get any detail beyond the P0700, just like my Predator reader/programmer.

Typically, the SES lamp is off for a few/several seconds after starting the engine, before it reappears. If using the Predator to reset the SES, the lamp will go out for a few/several seconds, before reappearing. I need to crawl under the truck and then wiggle the electrical connector to see if that has an effect. I do know that the SES remained off after the last full service, which I suspect may have been due more to incidental movement of the electrical connector than the service itself. The pan had been dropped during the service to R&R the internal pan filter. There was very little in the way of sludge or particles in the pan and the ATF looked pretty new.

Annotated Allison code list: https://www.thedieselpage.com/member...sondtclist.htm

That is curious. If I'm understanding, you are clearing DTC's while running(?) and it reappears in the same session before changing any conditions (such as driving, changing gear selection, restarting)? That is not a transient fault, and it should be, at least, leaving a trail of codes in history. If you aren't seeing limp mode, the P0700 is a soft code, and shouldn't be persistent as it is. Any code that repeats after clearing, in the same session, or a specific number of successive sessions, will print in history. A Snap-On code reader, if that's all it is, shouldn't be able to read TCM codes. They're intended for general ECM DTC's and emissions inspection readiness. I use a Zurich ZR15S, which is a full function bidirectional scanner. It easily reads TCM data and DTC's, as well as historic codes, pending codes (incomplete tests), and all the real time data any of the control modules are capable of showing. A bidirectional scanner may be required to command the TCM to dump it's codes and data, which is true for most other control modules (BCM, ABS, SRS, etc.). I got the scanner primarily to access EV functions and data. GM EV's have a few more control modules that most code readers and many scanners don't know about.

Quote:

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Originally Posted by DmaxMaverick

That is curious. If I'm understanding, you are clearing DTC's while running(?) and it reappears in the same session before changing any conditions (such as driving, changing gear selection, restarting)? That is not a transient fault, and it should be, at least, leaving a trail of codes in history. If you aren't seeing limp mode, the P0700 is a soft code, and shouldn't be persistent as it is. Any code that repeats after clearing, in the same session, or a specific number of successive sessions, will print in history. A Snap-On code reader, if that's all it is, shouldn't be able to read TCM codes. They're intended for general ECM DTC's and emissions inspection readiness. I use a Zurich ZR15S, which is a full function bidirectional scanner. It easily reads TCM data and DTC's, as well as historic codes, pending codes (incomplete tests), and all the real time data any of the control modules are capable of showing. A bidirectional scanner may be required to command the TCM to dump it's codes and data, which is true for most other control modules (BCM, ABS, SRS, etc.). I got the scanner primarily to access EV functions and data. GM EV's have a few more control modules that most code readers and many scanners don't know about.

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I don't think the code clearing was done while the engine was running. But, the P0700 (and SES lamp) does return a few seconds after clearing and then re-starting. Of course, the code is read after shutting off the engine. I know I tested the "check/reset" with the engine running a while back, but I don't remember the details, as to whether I could clear it or not with the engine running.

If a reader/scanner is capable of clearing codes under any condition, it will clear codes engine running or not. Given the opportunity, I will almost always check/clear during the same run session, then try to repeat the conditions before a restart. Some diagnostics only run during a cold start (such as a glow cycle), and/or after a specific number of starts or warming cycles. A high class code in history, even if erroneous, can override clearing the code, and relight the SES. P0700 won't do this, so if it returns, the TCM is still seeing the condition that set it and requests the code and SES. If P0700 is that persistent, there must be an underlying code. You need a bidirectional scanner to clear codes from history, so they should be there. Anyone with a smog inspection in the near future should be careful of this. Clearing history will also reset ALL the smog diagnostics, and restart them from the beginning. It can take days or weeks to get them all to clear. Learned that the hard way.

https://www.youtube.com/watch?v=20JXJx-luNQ

This video is an introduction to Duramax 6600 diesel service - This video is the first in a series that will eventually show how to do everything listed here, but first, let's talk about what tools, tips and procedures are necessary to complete a fuel injector replacement, cylinder head gasket replacement, water pump replacement and much more.

Can't wait for the video series to be complete? Would you rather have a complete printed Duramax Diesel Service Guide now?
See: https://www.thedieselpage.com/durama...rviceguide.htm

If you're interested in learning more about Duramax 6600 service and repair, then the introductory YouTube video shown here would be the best place to begin. We've helped thousands of Duramax owners with their own service work through the years. We can help you too.

Our YouTube channel is new, but its growth will help us to provide so much more - at no cost to you.

You can help! Please subscribe to our Youtube channel - run your mouse cursor over the little circle truck image in the upper left of the video shown here. Please Like and Subscribe, and post your comments on YouTube.

I recommend that you create a YouTube account. It's easy and free to register at YouTube.com, plus you'll be eligible for free stuff here in The Diesel Page very soon. By the end of July 2024 we'll begin offering all member-only online content here at TDP free of charge to those who are subscribed to our YouTube channel. Your YouTube account name will be linked to the free access list.

TDP's long-term goal is to produce more free content videos, some derived from some of the several books we offer. The first book to be transformed into a video will be the "Duramax Service Guide". This book is, in my opinion, the most valuable book we offer. We're very close to uploading the next Service Guide video. The next one will be about Duramax injector replacement and the video after that will be about head gasket replacement - using the same sort of format used here in this introductory video.

Subscribing to TDP's YouTube channel will ensure you don't miss any new videos. As always, your input, suggestions and advice are all important.

The cooling system in our project truck (Lil Red) was filled with the red/orange colored Dex-Cool coolant back in the spring of 2004. While a little was lost during the head gasket replacement in August of 2021, most of the original fill was saved and re-used. It still looked as fresh as new. Keeping the drained coolant clean is required if anyone wants to re-use it.

Our 2001 GMC Duramax had its head gaskets replaced in the June of 2021. The coolant looked great (like new) and most of it was kept clean and re-used. I could see a lot of the internal areas of the engine's cooling system with the heads off. The internal areas looked practically new. There was no visible indication of corrosion in any of the aluminum, cast-iron, steel or any other component wetted by Dex-Cool coolant.

We used Dex during the September 2021 rebuild completion and install of my daughter's 1994 6.5L Turbo Diesel Chevy Blazer engine. The radiator and heater core were flushed before hand, due to its having used the green coolant from new. The vehicle sat since 2009 till getting the engine running again after the rebuild. In the years since 2021 and getting the Blazer back on the road, there have been no coolant related problems (or problems otherwise).

Conclusion... Dex-Cool is a great!

Upcoming will be a new video showing the Duramax engines during the disassembly/re-assembly process of having their head gaskets replaced. You'll get to see inside both engines. The Youtube video should be available sometime near the end of this September. I'll announce it here when it goes live and you'll be notified by YouTube if you're subscribed to our channel. :) Jim

https://www.youtube.com/watch?v=QQ1D1FUk1zs

Duramax Diesel How-To video series! This video will show you how to correctly remove and replace the LB7 Duramax 6600 diesel fuel injectors. This video is part of a series of service videos (available now and upcoming), all designed to help you perform your own service work, save money and get a better result.

To learn more about the "Tools, Tips and Supplies" you'll need when working on your Duramax 6600, watch this video first:
https://www.youtube.com/watch?v=20JXJx-luNQ

Can't wait for the video series to be complete? Would you rather have a complete printed Duramax Diesel Service Guide now?
See: https://www.thedieselpage.com/durama...rviceguide.htm

If you're interested in learning more about Duramax 6600 service and repair, this series will be a big help to you. The Diesel Page has helped thousands of Duramax owners with their own service work through the years. We can help you too.

Our YouTube channel is new, but its growth will help us to provide so much more.

You can help! Please subscribe to our Youtube channel - run your mouse cursor over the little circle truck image in the upper left of the video shown here. Please Like and Subscribe, and post your comments on YouTube or here.

Subscribing to TDP's YouTube channel will ensure you don't miss any new videos. As always, your input, suggestions and advice are all important.

Want to share this thread with others or help us get the word out about LB7 Duramax Head gasket and Fuel Injector Replacement? It's easy! Simply copy the following link and paste it into another forum post, email message or social media site:

www.thedieselpageforums.com/tdpforum/showthread.php?46717

https://www.thedieselpageforums.com/...4&d=1744218470

Turns out, a proper LB7 injector cup removal/re-installation really isn't all that complicated. Shown above is the machined deck surface of an LB7 cylinder head illustrating the appearance of a properly installed injector cup(s). If you run your finger over the end of the cup, you'd just barely feel the end of the cup protruding above the deck surface. Only .004" was removed from the deck when this head was re-surfaced. While hard to see in this image, there was a barely visible ring of red Loc-Tite 272 around the end of the cup, indicating that the proper amount of sealant was uniformly applied and distributed as the cup was driven into the head. The Loc-Tite not only seals the cup once cured but also lubricates the end of the cup as it's inserted into the head. Can't install them without this sealant - they won't go in without the lubrication qualities of the sealant.

https://www.thedieselpageforums.com/...3&d=1744218470

From the top side, you can see the correct position of the cups after being inserted into the heads. The video link in a previous post will show you how to properly insert each cup. For the sake of more info, the 2 large O-rings that seal the top (big end) of the cups in the head are lubricated before being inserted. I've heard of many different recommendations for a lubricant... ranging from liquid dish soap to coolant to engine oil to chassis grease. Now, these O-rings seal engine lubricant from reaching the engine coolant (or vice-versa), so from a practical standpoint, there are multiple correct answers as to which might be best. I chose to use a light coating of clean chassis grease, applied to both the O-rings and the inside of the top-side hole in the heads. The small-end of each hole should remain spotlessly clean and dry before receiving the Loc-Tite 272 sealant. It's been 4-1/2 years and nearly 20,000 miles since these photos were taken, without a hint of a coolant or oil leak. The above video link will show more detail.

Jim

PS... The printed Duramax Diesel Service Guide linked below in my signature will soon go away. There are currently just 3 of the beautifully printed versions remaining. Once they're gone... they're gone, and won't be printed again. My goal is to make every chapter of that Guide available in video format. You can help make that happen by supporting our YouTube channel and this video series with Likes, by Subscribing and posting comments to our YouTube posted videos.


Did this forum thread or YouTube video help you with servicing your Duramax? Would you like to share this information with others or help us get the word out about Duramax Head Gasket/Injector Replacement? It's easy! Simply link to us in your own YouTube video, or post the link(s) shown here in a forum post, email message or social media site. Thank you!

www.thedieselpageforums.com/tdpforum/showthread.php?46717
YouTube Channel - http://www.youtube.com/@thedieselpage

Thanks for the heads up on the amount of manuals left. Update there are only 2 left now.
As my towtruck is on my have to repair list for hard rad hoses...
The manual is on it's way, not that the manual will move the tow truck up the list of priorities any faster.
Thank you Jim for all you have done.

Quote:

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Originally Posted by Yukon6.2

Thanks for the heads up on the amount of manuals left. Update there are only 2 left now.
As my towtruck is on my have to repair list for hard rad hoses...
The manual is on it's way, not that the manual will move the tow truck up the list of priorities any faster.
Thank you Jim for all you have done.

---

Thank you Thomas!

Got the book safe and sound
I haven't been getting much shipped from the states lately and it showed. Had a brain fart and should have had it sent to my Alaska address. Probaly would have saved $50.00 by doing it that way. But seeing the tow truck is a company truck i will be claiming the costs as a business deduction
I usually discuss shipping ect to try and cut costs.So it turned out expensive, but in the end it will be worth it as it is an awesome book full of the information required to take on the job by yourself.
Customs is taking the tariff stuff seriously...had an additional $29.00 to pay to get the book out of jail.

While I certainly agree that shipping to Canada is too high, the cost to ship to the EU and the AU/NZ/SA is nearly twice that. We used to ship a lot of books to many countries around the world. Not so much these last several years. Shipping cost is why. Costs crossed a threshold.

I have quite a few friends, acquaintances and business contacts across Canada. My dad was even thinking about moving the family to Smithers in the late 1960's. At 16 I still remember the mini-skirts while driving through Williams Lake at 3:30 pm when the local high school got out in March 1969. The contrast of seeing mini-skirts on all the high school girls and 4 feet of snow on the ground made quite an impression on me. ;) I have also wanted to go to Bella Coola since the late 1960's when I read an article in Reader's Digest about a migrant homesteader who built his own seaplane so he had better access to his own little piece of paradise.

I recently helped a social media automotive enthusiast in Ontario who is looking to do a build series on a Duramax swap. And, I've been to Abbotsford BC quite a few times since 1997 to attend BD's dyno days. Brian Roth and his crew were always great to me. He told me once how he needed to frequently adapt their business to include the ever-changing monetary exchange rate. The last HD 12KGVW trailer I bought was made in Manitoba. I loved that trailer - wish I still had it. I don't like the neighborly squabbles between our respective govs, but imagine if we all used the USD with no tariffs, duty, customs or penalties in either direction. Shipping cost to the YT from Montana should be the same cost as shipping to Colorado. So yes, we like Canadians here!

Myself being born in the USA i keep an interest in what happens there. Americans are always welcome here
Had i been in the US for the last election i would be very happy with the results
Today is a very pivotal election here. It has so much consequences as to what will become of Canada.
I am very concerned.Never has the thought of leaving Canada been part of my life as it is now.
Unfortunately my life was never built around possibly moving.I have 3 yards full of vintage vehicles, my construction equipment and buildings.But if the fears i have about what path Canada takes today may force my hand and i may be spending the next few years liquidating and searching for my semi retirement home outside of Canada.
Unlike the blowhards that yell how they were going to leave the USA because of their hate for a person, my choice will be based not on hate. But based on my love of freedom, which could be a forgotten right depending on the path Canada elects today.
Sorry for a political base reply.

https://www.thedieselpageforums.com/...4&d=1747065410

I'd bet most Duramax owners (who have looked at fuel rates) have seen injector balance rates that were better than the above image. Ideally, we'd like the balance rates to be all nearer to zero - or at least below 1.0. The above image was taken in the summer of 2021 soon after completing the head gasket and injector replacement project in my 2001 GMC crew cab. As some of you may recall, I installed brand new SAC injectors. I have to say that I was a little disappointed to see four of the numbers as high as they are shown here (cyl 1, 2, 6 & 8 ??) with zero miles on the new parts.

I recognize that many factors can affect balance rates - such as engine mechanical parts and of course injector uniformity. Things like uniformity in cylinder compression and uniformity in valve clearances can affect injector balance rates, and these are just a couple of the factors I've considered. Then, there's always the possibility for contaminating critical parts during the reassembly. I'm pretty good at keeping things clean, and I am not afraid to use/begin with a power washer, brake cleaner, clean shop towels, powerful shop vac, and beginning important work with a clean shop. I trust my work more than anyone else's to keep things clean. But, the above image did haunt me. I always use fuel treatment - injector cleaner, lube, cetane, etc. I had hoped that with time and miles, the injectors would "settle in". They didn't...

Over the past few months, I've noticed a bit more roughness in the engine when cold. I know that the automatic fuel-rate balancing doesn't begin till the engine has reached at least 100 degrees (IIRC). The engine did smooth out some when it reached operating temp, when the programming began to balance the fuel-rates. But, it never got to what I would call smooth...

About 10 days or so ago I noticed the exhaust would produce a bluish/white exhaust color (quite pronounced) when lightly accelerating, even at operating temperature. It would slowly go away, and then the exhaust would look more or less normal (clean). But the exhaust color would come back if (for example) you stopped at a stoplight, then pulled away. I noticed that what symptoms I'm discussing here had somewhat deteriorated over this past year... Then, a few days ago I pulled out my Predator programmer and looked at the injector balance rates again...

https://www.thedieselpageforums.com/...5&d=1747065410

This is what I saw... The engine was at operating temp when these numbers were taken. They're awful. But if we can assume the "12.82" number is #7, it would be logical to assume that that high positive value is causing all of the others (except 2??) to go negative to compensate. If #7 was where it was when first installed, the numbers might be closer to where they had been originally.

Or, I could be thinking about this backwards... Maybe the 12+ for #7 is an attempt to compensate for an imbalance... I'll try to get the commanded fuel pulse width data as Greg mentioned in a PM to me.

https://www.thedieselpageforums.com/...6&d=1747065410

Before unplugging the Predator, I looked to see if any trouble codes were present. The truck wasn't showing a Service Engine Soon light, but... sure enough, it had a P0307 in memory "#7 Misfire Detected", which sets when the injector fuel rate for one or more injectors is/are outside tolerance.

As you may recall, I installed a set of SAC injectors instead of the OE VCO injectors... SAC type injectors are advertised to produce a longer life when compared to the original factory VCO type injectors. As of today, these injectors have just 18,000 miles on them. The engine's original factory-installed VCO injectors were replaced with 120,000 miles on them...

All this was made more apparent late last month when I pulled Lil Red out of storage for the first time this year. That engine runs incredibly smooth when cold and like butter when at op temp. As you may recall, I replaced the heads gaskets and resealed the injector cups in that engine a couple months after replacing the head gaskets in my 2001 GMC in 2021. I was careful with Lil Red's engine as well, to keep the fuel injection system clean and uncontaminated. Both trucks got a new Baldwin fuel filter during the process.

So, what do we have here? Were the SAC injectors a wrong choice? Or, is something else going on? :(

Jim

https://www.ebay.com/sch/i.html?_nkw...023.m570.l1313

Repair possibilities:
1- Get a set of eBay nozzles/pintles along with the special tools, and see how it goes... LB7 nozzles/pintles are going for about $45 for each injector or $360/set of eight.

2- 8X Genuine BOSCH OEM Fuel Injector 0445120008 For 2001-2004 Duramax LB7 6.6L Brand New for $749

Last option... pay another $2400... :eek:

The "Balancing Rates" are the correction values, and not necessarily an indicator of a condition. A cold start, usually less smooth compared to warm/balancing temp, is zeros across the cylinders. Equally important is the PWM (Pulse Width Modulation) rates. The "Balancing Rates" indicate the commanded fuel volume adjustment, while the PWM indicates the electric pulse duration for that event. I don't know that it's even possible to have an actual balancing volume as high as +12. That's a lot of fuel at idle, or low RPM/load. I'd be curious what the GP looks like for that cylinder, compared to a more "normal" cylinder. I would suspect an issue with not only the injector but, as you suggest, another offender involved, such as compression loss, for whatever reason.

Mine has a lazy injector (#7 also, incidentally), that slightly overfuels, only at idle and off-idle power, but clears up and smooths out perfectly at higher RPM's and/or loads. It's barely noticeably different between cold and warm, but more noticeable with balancing disabled when warm (1% APP angle disables the balancing, w/o increasing engine speed). My balancing rates and PWM's are all within spec. when up to temp. The injectors were replaced in 2007, just before exceeding the time limit of the extended injector warranty. The injector issue showed up at about 13 months after the replacement, so the dealer wouldn't consider any action not on my dime. The truck has only about 30K miles since then, and the issue is exactly the same as when it first appeared. No smoke, no excessive EGT (thermocouple is on #7 exhaust port), no fuel in the oil, and no complaints from the computer. If it doesn't get worse, I'm not too worried about it.

Another thing that occurred to me is, that injector may not be atomizing the fuel (streaming). It would require additional fuel for an equal combustion pressure (balance), and would show as white smoke at the exhaust. If that's the case, the result could be catastrophic, very quickly.

Quote:

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Originally Posted by DmaxMaverick

The "Balancing Rates" are the correction values, and not necessarily an indicator of a condition. A cold start, usually less smooth compared to warm/balancing temp, is zeros across the cylinders. Equally important is the PWM (Pulse Width Modulation) rates. The "Balancing Rates" indicate the commanded fuel volume adjustment, while the PWM indicates the electric pulse duration for that event. I don't know that it's even possible to have an actual balancing volume as high as +12. That's a lot of fuel at idle, or low RPM/load. I'd be curious what the GP looks like for that cylinder, compared to a more "normal" cylinder. I would suspect an issue with not only the injector but, as you suggest, another offender involved, such as compression loss, for whatever reason.

Mine has a lazy injector (#7 also, incidentally), that slightly overfuels, only at idle and off-idle power, but clears up and smooths out perfectly at higher RPM's and/or loads. It's barely noticeably different between cold and warm, but more noticeable with balancing disabled when warm (1% APP angle disables the balancing, w/o increasing engine speed). My balancing rates and PWM's are all within spec. when up to temp. The injectors were replaced in 2007, just before exceeding the time limit of the extended injector warranty. The injector issue showed up at about 13 months after the replacement, so the dealer wouldn't consider any action not on my dime. The truck has only about 30K miles since then, and the issue is exactly the same as when it first appeared. No smoke, no excessive EGT (thermocouple is on #7 exhaust port), no fuel in the oil, and no complaints from the computer. If it doesn't get worse, I'm not too worried about it.

---

It's an assumption on my part that the ordered list of fuel rates shown on the Predator programmer begins with #1 cyl at the top and with cyl #8 at the bottom. I'll pull the #7 glow plug when I have time... I'm curious too.

Like your truck, at speed, any balance rate issue is not noticeable. It seems to hit on all 8 just fine. But the slow speed accel smoke is unacceptable and the idle roughness is a worrisome irritation.

https://www.thedieselpageforums.com/...8&d=1747165779

The above was the pulse width data at idle in Park.

https://www.thedieselpageforums.com/...7&d=1747165779

The above fuel trim data record and the pulse width data were recorded just minutes ago after a 55 mile trip, mostly at 65-70 mph. The fuel rate/trim for #2 & #7 have gotten worse.

And, the P0307 came back, after it had been reset yesterday. Still no SES.

Don't know what it all means yet. I was doing a little reading on the internet this morning, trying to find info for the symptoms I'm seeing. While I couldn't find the exact same symptoms, I did find a couple of posts that reported similar results... The recommendations for them included running a GM diesel fuel system cleaner through the system, or others suggested changing out the injectors. Yet another suggested running the truck hard for a couple of hundred miles. I will admit, that my truck hasn't seen much serious work since the injector replacement (I usually drive easy - for fuel economy).

I still have a question about Duramax "injector knock" some have talked about online. I have heard an injector knock on a 6.2L diesel... That one sounded like a rod knock - exactly like a bad connecting rod bearing. In that case, stopping fuel flow to that injector stopped the knock cold.

In my case, the Duramax is periodically clattering more on just one or two cylinders while lightly accelerating. I wouldn't call it a "knock" - it's diesel clatter, like the pilot injection had been turned off for one or two cylinders. And, it's still producing bluish/white smoke periodically on acceleration. I haven't noticed it at idle, even when kneeling down at the tailpipe.

I've got a trailer to tow in about 10 days that will weigh quite a bit (20' enclosed trailer loaded with household belongings). That pull, over a mountain pass would help clean out the carbon! I do know that back in my 6.2L diesel days, that my 6.2 always ran better after a trailer towing trip.

Those numbers are way off the norm. I'm really surprised you aren't seeing the SES lamp. The P0307 is, apparently, transient, and remaining in history. Use a more capable scanner to read if it's active or in history, relative to ignition cycles. Comparing the progression of the rates you're seeing, the offenders have seemed to change with each reading (posts), and are now at #2 and 7, and worsening. With fueling imbalance that bad, the engine should be loping wildly when cold.

#2 and 7 are opposite ends of the banks, but the same locations relative to the heads. The early LLY models had issues with the injector harnesses at those cylinders, with initial increased impedance (and corresponding PWM rates), then open circuits that shut down those cylinders completely (recall TSB for that issue).

I'm wondering if you're having a contamination issue, or something else that may be as immediate. When you to the test again, also include idle in D (E-brake applied). Adding a little load at idle should (in theory, ha) show more even rates across the cylinders, or a more wild variance. A drive gear selection also changes/reduces the piloting events. Watch for the SES lamp, which may come on/off only temporarily during specific conditions.

This is what mine looked like this morning, ECT at operating temp after a short drive:

PWM
Attachment 8009

Balancing
Attachment 8010

PWM, in D
Attachment 8011

Balancing in D
Attachment 8012

Notice in D, the PWM's increase while the Balancing Rates of all cylinders move considerably closer to zero. In D, the Diesel clatter is slightly louder, but the engine remains smooth.

Another symptom to look/listen for is ign-off fuel leakage, which can cause engine oil contamination, and more serious issues if excessive. If, after a warm shut-down, and a period of time passing (5-20 minutes), cranking produces an ignition knock just before it starts and runs normally. That knock is fuel that has leaked into a cylinder(s) after the last running cycle, that ignites in a warm cylinder prior to the normal injector events begin. Mine did this often, before the last injector replacement in 2007, but not once, since.

Your numbers look pretty good by comparison... I've been checking the engine oil level pretty regularly, thinking that a leaking injector might cause fuel dilution. So far, there hasn't been any odd oil level indications.

I drove the truck into town today, and it behaved much better - no smoke and not nearly as much clatter. Seems odd... if it's due to a degradation of an injector, one would think it'd be pretty consistent. But, it's not been, and I suspect the symptoms will shift as they have before.

Quote:

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Those numbers are way off the norm. I'm really surprised you aren't seeing the SES lamp. The P0307 is, apparently, transient, and remaining in history. Use a more capable scanner to read if it's active or in history, relative to ignition cycles. Comparing the progression of the rates you're seeing, the offenders have seemed to change with each reading (posts), and are now at #2 and 7, and worsening. With fueling imbalance that bad, the engine should be loping wildly when cold.

#2 and 7 are opposite ends of the banks, but the same locations relative to the heads. The early LLY models had issues with the injector harnesses at those cylinders, with initial increased impedance (and corresponding PWM rates), then open circuits that shut down those cylinders completely (recall TSB for that issue).

I'm wondering if you're having a contamination issue, or something else that may be as immediate. When you to the test again, also include idle in D (E-brake applied). Adding a little load at idle should (in theory, ha) show more even rates across the cylinders, or a more wild variance. A drive gear selection also changes/reduces the piloting events. Watch for the SES lamp, which may come on/off only temporarily during specific conditions.

---

I didn't see this post till tonight, I'll let you know what I see. In the meantime, I do know that you can feel/hear the difference in smoothness when in "D", at idle with foot on the brake. Seems like a cyl is dropping or not contributing in D, but seems to run smoother in park.

https://www.thedieselpageforums.com/...5&d=1747843686

Both images here are with the transmission in "D" at idle, engine at operating temp.

https://www.thedieselpageforums.com/...4&d=1747843686

As an addition... The engine has always had a bit of a lope at idle (comes and goes) - at least since it was a year old or so, caused by a variation in Fuel Rail Pressure. Never a rail pressure code, or does it seem to affect the engine running otherwise. At idle, the FRP is shown to be about 30 Mpa and varies about 8 or so. That may contribute to the balancing numbers shown here. At 2000-rpm, in neutral, the FRP is shown to be about 60 Mpa with almost no variation.

How do you identify a bad injector using the above numbers?

Quote:

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Another symptom to look/listen for is ign-off fuel leakage, which can cause engine oil contamination, and more serious issues if excessive. If, after a warm shut-down, and a period of time passing (5-20 minutes), cranking produces an ignition knock just before it starts and runs normally. That knock is fuel that has leaked into a cylinder(s) after the last running cycle, that ignites in a warm cylinder prior to the normal injector events begin. Mine did this often, before the last injector replacement in 2007, but not once, since.

---

I assume you're referring to a "ccrraacckk" at startup. I really noticed it with the SAC injectors from the beginning. Though there hasn't' been any fuel dilution in the engine oil.

Quote:

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Originally Posted by More Power

.....
I assume you're referring to a "ccrraacckk" at startup. I really noticed it with the SAC injectors from the beginning. Though there hasn't' been any fuel dilution in the engine oil.

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Mine has always done that. Before and after injector replacements (mine's had 2, as well as a separate return line replacement after filling the crankcase with fuel, after the first injector replacement). A long cranking (3-4 seconds), "ccrraacckk", then settles into an idle. That's every cold start since new, right up to this morning.

The "knock" I'm referring is a single ignition event, during the long crank before a start. Most often after a warm shutdown, and a start between 5 and 20 minutes later. It is a noticeably different event that isn't part of the fuel injection events after the long crank, "ccrraacckk", and idle. This happens happens between turning the key and actual fuel injection events. I suspect it's between 5 and 20 minutes because, less than 5 minutes doesn't leak enough fuel for a noticeable knock, and longer than 20 minutes allows for the fuel to dissipate (in one way or another). It was repeatable for the dealer tech, and was diagnosed as a leaking injector, resulting in the last warranty injector replacement.

Those numbers are horrible. Much worse, progressively, than the first pics you posted in #147. Increasing the fuel volume that much suggests a significant fuel restriction, not related to the fuel rail pressure and control (if so, it wouldn't be isolated to just 1 or 2 cylinders, consistently), or perhaps a sensor or calibration issue. Is any calibration modification (program) installed? I mean any, even if at "stock" power. Check if the "restore to factory" option is available in the Predator. That will be the last factory PCM calibration copy it made prior to any modification. I had some errors with instrumentation, fuel temp faults, and loss of speedo calibration over a period of time, and the restore immediately corrected all of that. I've modified the calibration many times since, and the problems haven't reoccurred. Restoring the factory calibration dumps all "learned" parameters, and forces a relearn of everything dynamic in the PCM. The injectors you're using right now are different than the previous data the Predator had copied. It's worth a try and, best of all, it's free.

Quote:

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Originally Posted by DmaxMaverick

Mine has always done that. Before and after injector replacements (mine's had 2, as well as a separate return line replacement after filling the crankcase with fuel, after the first injector replacement). A long cranking (3-4 seconds), "ccrraacckk", then settles into an idle. That's every cold start since new, right up to this morning.

The "knock" I'm referring is a single ignition event, during the long crank before a start. Most often after a warm shutdown, and a start between 5 and 20 minutes later. It is a noticeably different event that isn't part of the fuel injection events after the long crank, "ccrraacckk", and idle. This happens happens between turning the key and actual fuel injection events. I suspect it's between 5 and 20 minutes because, less than 5 minutes doesn't leak enough fuel for a noticeable knock, and longer than 20 minutes allows for the fuel to dissipate (in one way or another). It was repeatable for the dealer tech, and was diagnosed as a leaking injector, resulting in the last warranty injector replacement.

Those numbers are horrible. Much worse, progressively, than the first pics you posted in #147. Increasing the fuel volume that much suggests a significant fuel restriction, not related to the fuel rail pressure and control (if so, it wouldn't be isolated to just 1 or 2 cylinders, consistently), or perhaps a sensor or calibration issue. Is any calibration modification (program) installed? I mean any, even if at "stock" power. Check if the "restore to factory" option is available in the Predator. That will be the last factory PCM calibration copy it made prior to any modification. I had some errors with instrumentation, fuel temp faults, and loss of speedo calibration over a period of time, and the restore immediately corrected all of that. I've modified the calibration many times since, and the problems haven't reoccurred. Restoring the factory calibration dumps all "learned" parameters, and forces a relearn of everything dynamic in the PCM. The injectors you're using right now are different than the previous data the Predator had copied. It's worth a try and, best of all, it's free.

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The current programming is factory. I messed up years ago with the Predator, and had to have the dealership reflash the ECM. Since then I've not needed or wanted the Predator programming. I use the Predator nowadays for the diagnostics/code reads/resets. However, I have thought that a reflash might help, because it's been a long time since. But, I hate having the dealer work on my truck.

Question... does the high balancing numbers on 2&7 indicate a problem with those injectors, or are they high because of others being too low? Thx

Quote:

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Originally Posted by More Power

....

Question... does the high balancing numbers on 2&7 indicate a problem with those injectors, or are they high because of others being too low? Thx

---

Normally, I would say no, not necessarily high/low because of indicated high/low cylinders. In my experience, it is not, as long as the PWM's track closer to baseline. However, I suspect #2 and #7 are suspect cylinders in this case, due to the excessive increase of only the 2 cylinders, high decrease of the remainder, with PWM's that track the balance rates, rather than the baseline. Also note, the scanner/programmer will show the cylinder rates in numerical cylinder order, opposed to actual firing order: 1-2-7-8-4-5-6-3. #'s 2 and 7 are adjacent in firing, which I would expect a cause for a lope, with them so far off of baseline, especially bad at cold idle before balancing begins. If you are actually seeing smoke, of any color, due to this, then I suspect a problem that isn't, at least wholly, limited to the injector(s). A physical or electrical condition is more suspect. Adding that much fuel to compensate for a mechanical shortfall may indicate that much additional fuel is actually occurring. Otherwise, I'd suspect either a sensor error, or an injector response delay (defective injector). If it were merely an injector that's having a difficult time keeping up with timing demands, electronically correcting it with additional (demanded) volume at a longer duration is still the same ultimate volume of fuel for that combustion event. If the balancing feature is able to generally balance the idle, then the electronic command adjustments are effective. If it were not able to bring the balance into a baseline default, it would code. Unlike fuel rail pressure regulation, the PCM demands a specific pressure, and receives feedback of the actual pressure, while the injectors are demanded a volume and duration, with no means of the PCM to know the actual result. The only feedback comes in the form of crank speed variations, provided by the high resolution CPK.

A high fuel rate with white smoke suggests at least one cylinder is getting more fuel than it has heat to fully combust. The appearance of the glow plugs and a compression test may be very telling.

Thanks. The "lope" has been with the truck at least since it went off warranty... now nearly twenty years ago, and now on its 3rd set of injectors. It comes and goes, or it has in the past. I think it's more FPR related. If I go into this engine again, I'll replace it.

I mention in the head gasket replacement portion of the service guide about being very deliberate when setting the valve lash and tightening the electrical connectors on each injector (and other fasteners) before installing the upper/lower valve covers. Those are areas of a head gasket R&R that can haunt your dreams otherwise. I have considered those areas as possible causes for the current situation, but one cannot tell without taking things apart.:confused:

https://www.thedieselpageforums.com/...2&d=1749658034

We went on a pretty tough towing excursion over the past couple of days. We rented a 20' enclosed car-hauler trailer. When loaded with household goods, I estimated it to weigh about 10K, which pulled like a parachute. For a rented trailer, everything worked... the lights, electric brakes and it even included two spare tires/wheels. The above photo shows the truck hitched to an empty trailer. When loaded for the return trip, both the truck and trailer were level - the beauty of a properly set up weight-distributing hitch.

https://www.thedieselpageforums.com/...3&d=1749672620

The rental company didn't have a weight-distributing hitch so we bought a new one from Harbor Freight. Turns out that new HF hitch was exactly like the one I owned in 2000 when we towed a 27' Fleetwood Mallard - first with our 6.5TD Power Project truck and then with the 2001 GMC Duramax shown in the first photo here. I like this hitch a lot. If anyone wants more info on this weight-distributing hitch or its setup, let me know. The above photo shows the hitch attached to our 6.5TD Power Project truck. The new hitch is just like it.

From the outset I was curious whether this tough towing excursion (included about 10 miles of 6% uphills at 1200+ degrees EGT and 200+ miles at 1000+ EGT on the Interstate at 70-mph) would change how the engine ran - i.e. would clean up the numbers a bit. A trip like this should address the question of whether or not carbon deposits on the injectors may be contributing to any of the problems seen here (i.e. cylinder balance and other symptoms).

The first two photos below were shot immediately after the last towing session - idling with the transmission in Park. The engine was running with completely stock GM programming with no power adders. Before the trip I thought about installing my tried and true Van-Aaken power module, which can smoothly add another 100 hp or more, but chose to keep the stock programming/power for better baseline discussion and troubleshooting. That power module actually decreases EGT while towing and makes towing in hilly country a lot more pleasant (less shift business).

https://www.thedieselpageforums.com/...6&d=1748541685

https://www.thedieselpageforums.com/...5&d=1748541685

The next two images represent the pulse width and balancing rates while the truck was idling in Drive - foot on the brake.

https://www.thedieselpageforums.com/...4&d=1748541685

https://www.thedieselpageforums.com/...3&d=1748541685

Conclusions... The numbers improved a little when compared to the images shown in an earlier post, and the sounds/response of the engine has changed a little. Still not smooth at idle - presents as a miss. And, abnormal injector rattle comes and goes at times while driving - depending on engine rpm and load. No codes - still not right. In the end, it got through this tow without blowing a gasket. Thankful for that. I was a bit concerned about driving it that far from home with this problem. No choice but to drive it. Seemed a little down on power, but delivered fuel economy about on par with what I remember.

If I'd had the trailer wiring/plug completed for Lil Red I would have been tempted to drive it. That might have been fun! Cool video!

Thinking I'll dig into the engine when I get a minute.........