Duramax Head Gasket Replacement

[More Power]

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.



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.


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[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.

[More Power]

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!

[Yukon6.2]

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.

[More Power]

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!

[Yukon6.2]

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.

[More Power]

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...



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.



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...

[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.

[DmaxMaverick]

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.

[More Power]

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.

[More Power]

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



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.

[DmaxMaverick]

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.

[DmaxMaverick]

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

PWM
20250514_idle-PWM-b.jpg

Balancing
20250514_idle-BR-a.jpg

PWM, in D
20250514_idle-D-PWM-a.jpg

Balancing in D
20250514_idle-D-BR-a.jpg

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.

[More Power]

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.

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.