Duramax 6600 - Low Power

[KMiller]

Original owner of 2002 Silverado with Duramax 1GCHK29182E119831

Never been on forum so not sure how to proceed but hoping someone out there can help point my professionals in the right direction. Tried to leave for long trip with 23' 5th wheel and struggled to get up to first hill after spending over $7,000 last week to fix low power upon acceleration (P1093 & P1094).



I'm also not mechanically inclined - have to trust the professionals that can't seem to get it fixed after putting in new fuel filter, Air Filter, and all new injectors (2nd set at 178,000 miles - dealer also replaced them at 73,588 miles). Some of the clues/tests/recommendations/notes on the bills I paid include:

• Dealer: Road tests inconclusive due to different faults possible - wait and see after first time codes appeared a year ago on way back from camping trip
• Independent mechanic with Duramax training:
  
  • "Inspected fuel hoses between Filter and Pump - changed one but all hoses are cracking and need to be changed with correct type of hose" (next expert at diesel shop[below] said they looked/felt fine so didn't change)
  • "Monitor BARO and Boost - Match 98 KPA @ idle and Boost 206 KPA @ RPM - Normal at time tesed - suspect Sticking Waste Gate"
  • "Monitor Suction side 4.5 in. @ WOT Park and 8.0 in @ WOT Driving"
  • "Control Pressure Reg. to max. 160 and no change in Act. Pressure"
  • Test Return Flow Cranking @ return line to tank - 60ML in 15 sec."
  • "Suspect Leaking Pressure Limiting valve or leaking injectors." (I believe he said his Duramax decision tree pointed to low pressure fuel side initially but some quirk in the decision tree [That I didn't understand] ultimately lead him to the high pressure side)
  • Referred to Diesel only shop as didn't have time & thought problem was deep inside motor (where he had limited experience) so made following notes for Diesel mechanic:
    
    • Inspect fuel hoses between filter and Pump and change at least one
    • Suspect leaking Pressure Limiting Valve, or Leaking Injectors
• Diesel shop determined:
  
  • Reviewed all the work done earlier this week and the recommendation/suspicions from that testing
  • the problem was identified as being the injectors with at least a few of them not working ("Noticed that several injectors when shorted the RPMS would not change"). Wanting to keep truck long term and short of time jointly decided to not test injectors further, just replace them.
  • "2 injector housing pulled up with injectors - installed 2 new injector housings with seals"
  • Seemed to not understand or discount(?) above recommendation to check "Pressure Limiting Valve" before and after installation of injectors
  • Felt that the fuel hoses between filter and pump seemed fine to him and that these low pressure fuel lines rarely have any problems so he chose not replace hoses.
  • Indicated I should still experience black smoke but it should reduce over time as exhaust system clears from injector problem.
• Finally out of the shops with trailer in tow yesterday I was nervous first few miles and then very concerned when couldn't hold 40-45 on steep hills where others including heavily loaded old VW Van passed me . Turned around after 100 miles - calculated 10 miles/gallon when identical trip/trailer got 14 when new. Black exhaust still very visible on any acceleration after 200 miles out of shop. Too late on Friday nite to get hold of anyone.

Plan to be at Diesel shop Monday morning, but have lost confidence after they were confident it was "fixed" and their dismissive attitude toward other recommendations. Still hoping to get a fix and salvage some part of our long planned trip to Alaska but need something specific for any of the three possible mechanics to try (with my money ).

What suggestions/observations do any of you have?

Desparate and extremely frustrated with truck? mechanics? both?

Ken Miller

[DmaxMaverick]

Welcome aboard! Sorry it has to be under these conditions.

I'll take some time and look over what you posted. Be patient, it's a long list. I'm sure others will jump in too, but don't be surprised if takes them a while. Like I said.....Long list.

In the meanwhile, have you tried a new fuel filler cap? Sometimes, things are no more complicated than that.

[cabletech]

How heavy is the trailer? Is the check engine light on? I would want to have mechanic test drive with trailer in tow. That should help them find the problem as they can check boost and fuel pressure under load.

Jay

[KMiller]

It's a 23' 5th wheel that should be relatively light (maybe 5,000# loaded - much lighter than some dump trailer loads of gravel I've hauled on mostly flat ground without noticeable problem) compared to most others I see on the road (all of which were passing me).

I did have dealer mechanic ride with me while towing the trailer (a year ago) and his computer readings were inconclusive at that time with the actual pressures being close to normal. Prior to doing this test last Sept the Check Engine light had come on - that's the only time that light has come on. it didn't come on last week when mechanic was seeing large difference between commanded pressures and actual pressures, nor did it come on Friday when we struggled to get up hill on I-90 going to Snoqualmie Pass.

Ken

[DmaxMaverick]

The codes, P0193/4, and the black smoke and low power may or may not be related, or entirely related. If any of the above causes a low-power mode (such as not being able to reasonably pull a hill), the low power is an indicator of "Limp Mode", and not necessarily a symptom in and of itself. I suspect that's probably what is happening: P0193/4 persistent, causing Limp Mode. This would limit the power output, and may/may not limit gear ranges available. In any case, the condition would limit your ability to pull a hill, especially with a load on.

The black smoke is not a condition of previous "overfueling", saturating the pipe with fuel (the previous injector failures). This would cause WHITE smoke, until it's burned off. Black smoke results from too much fuel injected than there is O2 to burn completely, with sufficient heat available. White smoke is caused by low temp burning. "Rolling Coal" is too much fuel for available air. Simple as that. A saturated pipe would continually blow white smoke until the fuel is gone. If it were closer to the engine, such as the exhaust manifolds, it may blow black, but would be gone after one hot run.

This is what I see, according to the symptoms and codes present (NOT addressing the "low power" yet, due to above reasoning).......

FRP regulator unable to control rail pressure within the specific range. I think it's stuck closed or unable to respond to commands, unable to "regulate" pressure below the pressure that will set P0193: 175 Kpa (25,400 PSI, maximum system pressure ceiling). The black smoke indicates overfueling under certain conditions, which may be due to excess fuel "leaking" at low demand on only a few cylinders. The "leaking" may not be a failure, if the fuel pressure is in fact, near/above 175 Mpa. Individual injectors may react to excessive pressure differently, and still be within spec during normal conditions. Continued operation with this condition may cause failure of injectors, and/or CP3 high pressure pump (excessive sustained load).

I suggest a test of the FRP regulator, at least. If it's been done (wasn't clear it was done properly in your description), it appears it should be replaced. If it's stuck on 160 Mpa (23,200 PSI, maximum operating pressure), then causes P0193 (peaks above 175 Mpa, such as under heavy load at higher RPM's), it's stuck closed. The P0194 code may be due to a bad FRP regulator, preventing the FRP sensor from ever receiving a consistent or expected pressure value. It appears the FRP regulator needs replacement, and possibly the FRP sensor (they can be damaged by persistent excessive pressure). However, it is also possible it is only the sensor, but the conditions are so specific, it's almost self-eliminating.

If this were my truck, knowing only what you know/posted, I would replace both, the FRP regulator and sensor.

I do not think you have a fuel supply restriction issue (fuel lines/filter). If you did, the pump would not be able to develop the high pressure causing the apparent issue. None of the symptoms or codes indicate a fuel supply restriction issue.

Also, it doesn't appear a bad fuel filler cap will help the conditions. If it's original, I suggest replacing it with the correct cap, due to age.

[KMiller]

thanks for the specific tests you recommend - that gives me something specific to give the mechanic tomorrow morning rather than just a rant.

Ken

[DmaxMaverick]

I really hope this helps, and gets you on your way. If you are taking this information to your mechanic, make sure he sees all of it. Not only my suggestions, but my diagnostic process. A suggestion is no good without the reasons why. Good luck!

[KMiller]

In reading through many of the posts/info on this website I'm tempted to look into some kind of code reader, if not too spendy, & if in fact they are:
- easy for non-technical folks to use?
- of real value to mechanics I might use if stranded somewhere?
- can be used to easily reset something that has occurred, but is hindering getting to the next town with diesel mechanic? I'm confused about the "limp" mode I've read about and whether it's related to transmission &/or motor - likely it's something designed to help you get to civilization and shouldn't be tinkered with unless know what you are doing?

Thanks again for the infomation that gives me more hope than I had before finding this website.

Ken

[DmaxMaverick]

"Limp Mode" can be either, engine or tranny (tranny codes will be "P07xx"). The effects (power level and/or gear range limitations) depend on the reason for the fault. Without extensive PCM reprogramming, you can't defeat it (nor would I recommend it). A shutdown and restart will often reset it (SES lamp will stay on, with a code stored), and it will stay away until the condition repeats (or a new one surfaces). And yes, Limp Mode is the "get me to civilization without killing my truck" mode. The condition may not seem convenient at the time, but will usually allow enough to get you there without being too uncomfortable. Usually, if it happens, a short shutdown period then restart will clear it. Find out why it happened (this is where a code reader is very handy), and drive accordingly to where you need to go with that in mind, to prevent a repeat. Often, conditions can be easily remedied on the spot in a short time (such as a MAF code -P0101, for example-, which can indicate a dirty MAF sensor, or dirty air cleaner element). I highly recommend some sort of a code reader for long (or remote) travels. One that doesn't require a Dick Tracy decoder ring is a step up (plain language reader).

[Kennedy]

Suspect Leaking Pressure Limiting valve or leaking injectors.

Possible, but highly unlikely-more later.


[*]the problem was identified as being the injectors with at least a few of them not working ("Noticed that several injectors when shorted the RPMS would not change"). Wanting to keep truck long term and short of time jointly decided to not test injectors further, just replace them.


There will not be a change in RPM when shut down as the ECM is controlling to 682 idle speed. This is a case where I'd be curious to know what the balance rates were doing.


Seemed to not understand or discount(?) above recom

mendation to check "Pressure Limiting Valve" before and after installation of injectors

The test is simple with the Tech 2. Command the pressure up to max and see if it goes there. If it does then the valve is not leakingIf it does not try bringing up RPM to see if it rises.

"Control Pressure Reg. to max. 160 and no change in Act. Pressure

This above pertains to the test I suggested above, but the result description is vague. Does he mean that the act pressure did not increase or is he saying that actual matched desired?


[*]Felt that the fuel hoses between filter and pump seemed fine to him and that these low pressure fuel lines rarely have any problems so he chose not replace hoses.[*]Indicated I should still experience black smoke but it should reduce over time as exhaust system clears from injector problem.[/LIST]

You should have little to no smoke with stock programming. Check the turbo and ducting for boost leaks particularly the hot side IC tube where it passes the Power Steering. Lots of rubs in this area and sometimes they rub through.


What suggestions/observations do any of you have?

Although rare, I've seen situations where the MAF sensor is bad and I've also heard of fuel psi sensors going bad. I doubt this is the case here, but this is something worth looking into. Since you seem to be fueling but not burning (black smoke) I'd lean towards an induction leak between the turbo and the engine.




Ken Miller

Please make a decision if you'd like to continue this discussion here (preferrably) or via email. I replied to your email first, but I'd prefer to keep this all in one place.

[KMiller]

We I'm still stuck and home with a truck and small travel trailer that won't go up hills without Codes 1093 & 1094 despite spending another $1,165 installing a new Fuel Rail Pressure Regulator & Sensor, plus a new fuel cap.

Diesel Mechanic again thought it was "fixed" because the "pressures were up" from what they were before. I insisted on hooking up the trailer and taking test drive with trailer while he monitored the problem. Didn't hardly get out of driveway before it was obvious on whatever monitor/tester he was using. Got on freeway ramp (test hill was 5 miles away) and accelerated hard in tow haul mode and the 1093 & 1094 (pluse a "boost code") codes came up again and this time the check engine light came on. Signed the last credit card bill indicating I would likely want to contest these bills if I ultimately found the problem in something they worked on - if not, I'll reluctantly pay in full.

Whined enough to the Chev dealer that I'm now moved to the head of there line (at least that's what they told me) for their top diesel mechanic to try to get a real diagnosis before I look at what appears to be the next step of replacing the fuel pump, or tear into motor to be able to actually do the test on the Pressure Limiting Value (& replace all inlet fuel hoses), both of which were supposed to be done by the Diesel "mechanic". I sure don't mind trying inexpensive potential fixes like $21 fuel filler cap but $5,000 for new injectors and $1,200 for FRP regulator and Sensor without any real supporting mechanic tests to confirm they were a problem just isn't right - shame on them, and shame on me for needing a fix so bad I was too trusting!

Thanks to all that have responded - I do/will share all this "brainstorming" with whoever I work with going forward.

Ken

[KMiller]

Thought I made a reply to last post yesterday but couldn't find it so must be doing something wrong. Will try again.

Yesterday the diesel shop replace the Fuel Rail Pressure regulator and Sensor. Also replaced the fuel filler cap. - all after reading this blog - didn't sound like he had any real opinion himself nor any suggested tests. After installation, the mechanic declared the problem "fixed" just as he did last Friday after doing the injectors. Having been already burned a couple of times I insisted on going home, hooking up our smallish travel travel and returning to the shop for more testing under load before we actually restarted our trip to Alaska. Surprise, Surprise - the problem codes reappeared before we even did the test drive. Test drive resulted in the 1093/1094 codes reappearing along with a "boost" code - and the Check Engine light came on while aggressively merging onto freeway traffic - before we even got to the hill. Pretty quiet in cab on way back to shop. Signed credit card charges but indicated I would likely be protesting some/all of the bill depending on what I eventually learned.


Whinned enough to dealer (supplying all the expensive parts) to get some special attention (I think??) this morning. Gave him my list of everything done so far (w/o solution) and the remaining list of potential real problems, mostly gathered from this forum:

• "leaking Pressure Limiting Valve"? (Tonight they told me there is no such thing in duramax so apparently I got bad info somewhere, or confused this with the "Fuel Rail Pressure Regulator"???
• Collapsing Fuel Hoses between Filter and Pump?
• High Pressure Injection Pump?
• Defective Fuel Filter base? (Primer button "wasn't working like it's supposed to" according to dealer tech this morning but didn't think that was the problem - said he could bypass it somehow to test.
• Computor?
• Injector Line Corrosion (I did find the ones taken out and got them to the Dealers top mechanic - who seemed very skeptical)
• Some of the work already done?
• Other?

After 5 hours of diagnostics with help from all other shop techs and help from GM tech folks (who now have a "case file?" on this) they are "leaning towards the High Pressure Injection Pump" but will provide recommendation in the morning.

If they are right I will be relieved, if they are wrong I will now be out about $10,000 trying to fix my truck and even more ticked off than I am now. Another observation that (except possibly for this forum) mechanics don't seem to have any respect/appreciation for the work/ideas of others unlike most other professionals I've worked with. I've maintained a great deal of restraint while trying to cajol large ego's into at least considering others idea/suggestions. Maybe this dealer mechanic actually sought and found helpful advise - not getting my hopes up.

I resent not getting my truck fixed last week and I resent that I had to try to learn something about my motor that I shouldn't have to know. Clearly I'm one of the unintelligent folks in this whole mess, but not the only one!

I will make a post when/if we ever leave town with a "fix" and another one if we actually make it to Alaska and back.

Ken

[DmaxMaverick]

This is as bad a case as I've ever seen. Not so much the problem, but the level of competence you've seen in the tech's. So far, they are just throwing parts at it, without doing any (or wrong) actual diagnosis. Almost like the service guy has an agreement with the parts guy.

You need to stay on top of the first code, P0193. Only one condition will cause this, either actual, or sensory. Had the diagnosis process been performed correctly (a condition of replacing the reg/sensor), it would have eliminated them, or indicated replacement. Having been replaced with no improvement (the "hard" way to test them), the remaining possibilities do not include the CP3 pump (high pressure pump), or a poor fuel supply (collapsed/blocked fuel line). There is either a signal interruption (bad wire/connection), low voltage (5V reference circuits), or bad ECM. Remember, the problem is excessive HIGH pressure. If the pump is weak, or there is a fuel supply shortage, for whatever reason, the pressure cannot be that high, AND have a failed FRP regulator and/or sensor. The final diagnostic solution is ECM replacement. I did not mention this earlier, as it's the last, most unlikely, and most costly solution (1/2 way to new injectors, probably double that, the way it sounds you've been treated). If the pump is bad, there are other issues causing the other codes. I don't think you have a difficult problem. I do think you have difficult help. I wish I could do more and get you on you way with confidence.

Conditions:

NO P1635 or P1639 codes present, current or in history (Boost and Baro sensors, the proper diagnostic process would have eliminated these).

The system currently NOT in "power-down mode" (also eliminated by the diagnostic process).

FRP sensor indication greater than 175 Mpa (which sets the P0193 and MIL).

IF you are seeing a "boost" code, it is very important. It wasn't mentioned earlier. IF this code is present, they are looking at the wrong diagnostic process (talking to the wrong end of the horse), if they consulted it at all. I did, and it's fairly straight forward.

Circuit voltage, continuity and impedance tests are imperative. If this has not been done, they are just throwing parts at it. Unfortunately, the wrong parts.

[KMiller]

Some clarifications needed for tomorrow's diagnosis process:

You need to stay on top of the first code, P0193. Only one condition will cause this, either actual, or sensory. Had the diagnosis process been performed correctly (a condition of replacing the reg/sensor), it would have eliminated them, or indicated replacement. Inlet Diesel did not do any diagnosis process prior to recommending/agreeing with your suggestions.

Having been replaced with no improvement (the "hard" way to test them), the remaining possibilities do not include the CP3 pump (high pressure pump), or a poor fuel supply (collapsed/blocked fuel line).
There is either a signal interruption (bad wire/connection), low voltage (5V reference circuits), or bad ECM. Remember, the problem is excessive HIGH pressure. If the pump is weak, or there is a fuel supply shortage, for whatever reason, the pressure cannot be that high, AND have a failed FRP regulator and/or sensor. To double check, you are saying the new regulator and sensor with no resolution by default means the problem is not with the High Pressure Pum or fuel lines??

The final diagnostic solution is ECM replacement. I did not mention this earlier, as it's the last, most unlikely, and most costly solution (1/2 way to new injectors, probably double that, the way it sounds you've been treated). I sure hope you are wrong but I will get this to the dealer tech in the morning. If this expensive I may have to just walk away from the truck and salvage whatever I can. Not sure what values are but likely not much over $12-14,000 if that at this point despite already putting half that much into it.

If the pump is bad, there are other issues causing the other codes. I don't think you have a difficult problem. I do think you have difficult help.(Not the dealer at this point - mainly so-called experts at Inlet Diesel, and a truck owner that was too agreeable and assuming folks knew what they were doing/had tested appropriately. The original effort by Interstate Auto seemed to be following testing protochols and watching my pocketbook.

I wish I could do more and get you on you way with confidence.

Conditions:

NO P1635 or P1639 codes present, current or in history (Boost and Baro sensors, the proper diagnostic process would have eliminated these).

The system currently NOT in "power-down mode" (also eliminated by the diagnostic process).

FRP sensor indication greater than 175 Mpa (which sets the P0193 and MIL).

IF you are seeing a "boost" code, it is very important. I believe there were "Boost" codes prior to doing the injectors and FRP regulator and sensor - A "Boost" code also came on while test driving with Inlet Diesel tech after FRP regulator and sensor installed. It wasn't mentioned earlier. IF this code is present, they are looking at the wrong diagnostic process (talking to the wrong end of the horse), if they consulted it at all. I did, and it's fairly straight forward.

Circuit voltage, continuity and impedance tests are imperative. If this has not been done, they are just throwing parts at it. Unfortunately, the wrong parts


Thanks for the feedback - again I will show this to dealer tech in morning before he makes his recommendations. As reminder, dealer last looked at this issue 11 months ago with inconsistent findings so we decided to not throw money at the problem (like I've been doing last two weeks). I didn't go to dealer with this problem because they didn't have the time I needed to meet orginal schedule. Today was there first shot at digging deeper for a solution to the current (& last Sept's original 1093 code & check engine lights) effort. Hindsight will ultimately illuminate all the mistakes including mine - unless I projected costs force me to bail on even having a truck until I can get finances in shape again - tough when all money coming out of hard earned retirement savings.

Ken

[DmaxMaverick]

We may have a miscommunication. I reread the entire thread, and need to verify the actual DTC. Is it P1094 or P0193? I started off my first reply understanding P0193, which appears to be wrong according to your replies and emails (I'm not normally dyslectic). It's what was pulled up when I went to the diagnostic process, and I didn't notice the difference, so it may be my fault. They are very different (opposites). If it is P1093, then Kennedy's recommendations are correct, and it leads to a fuel restriction and/or the high pressure fuel pump (can also be injectors, but you shouldn't be seeing this with them recently replaced). Also, pursue the fuel line replacement if they appear to be deteriorated or damaged. In any case, the tech on a test drive with you should have caught this, and actually seen the fuel pressure results on your test drive, before and after. If the fuel pump is unable to reach or maintain commanded pressure, any component between the HP pump and tank, including an air leak, are suspect. It's hard to believe any competent tech would follow another's recommendations w/o reading the full diagnostic. He should have at least questioned it. Be sure to have the dealer VERIFY.

[Kennedy]

While not likely to help the problem, a lift pump in my opinion is mandatory and will help to locate issues like leaks as well as overcome restriction and prevent hose collapsing.




Preliminary diagnosis should be all of about 30 minutes to an hour:

Step 1 (done) measure system restriction at idle Should be in the neighborhood of 2-3"hg and move up very little at 3,000 rpm no load

Step 2 Use Tech 2 to command max psi at idle and see if actual psi follows or lags. If it lags give it a bit of rpm to see if it picks up

Step 3 Use Tech 2 to monitor desired vs actual while driving.


And no plastic crap fuel filters! I have my doubts about several other cheap looking filters, but haven't tested/dissected yet just get a bad vibe looking at some of them.




Measure restriction yourself and speed the process. Every Dmax owner should keep one of these (along with spare filters and tools to change) in the vehicle:

[KMiller]

As far as I know both codes 1093 and 1094 are both appearing.

John: Are you talking about the factory/dealer filler cap/crap?

Could it be that the test for the Fuel Rail Pressure regulator requires hooking up to something inside the motor - if so that would help explain the confusion on this end between the terms "Pressure Limiting Valve" and "Fuel Rail Pressure" regulator.

Heading to dealer right now with whatever they can glean with your latest posts.

Thanks again,

Ken

[KMiller]

P.S. Both the original mechanic at Interstate and the Dealer tech have tried to use their instrument to increase the speed of the motor to test pressures and neighter could get a motor response to commands that should have the motor racing. Maybe thats helpful??

[Kennedy]

Wix plastic filters. I'm getting more and more calls and they just put one of these plastic housing fuel filters on (tapers at top is telltale) and in many cases simply changing the filter fixes the issue.

At this point there is so much info spread over so many posts that it would be nice to have a review to put all in place in minimalistc fashion ie:

Injectors at 68 k by dealer

Problem at 125k (P1093 low pressure during power enrichment) (P1094 low pressure during decel/idle)

Injectors again 149k (no change) by diesel shop

Pressure sensor and regulator at 152k (no change)

[Kennedy]

To put things into perspective you said that under load the restriction was 8"hg. This is equivalent of 4 psi. That means whatever is outside (air) is trying to get inside with a 4 psi force. Adding a lift pump(s) to put a positive push on the fuel flips this the opposite direction. In other words say you have 4 psi lift you have made an 8psi change in the pressure inside so now there is a 4 psi force trying to get out. No air intrusion and if there is a leak it will show.


Let's take this further. Please feel free to correct my facts here as I am going by memory and have been unable to verify.

Diesel Fuel has a vapor pressure of approx 8-9 psi depending on temperature. The higher the temp the higher the vapor pressure. I'll use 14 psi atmosphere as a round number. Remove 4 psi (8" hg) from this and you have 10 psi in the lines. Getting pretty close aren't we? Add a little restriction to the filter or load to the truck or drop in atmospheric pressure and you are there. In normal operation you have diesel fuel "fizzing" in the lines due to outgassing.



I smell a new Tech Tip coming...