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Duramax 6600 Welcome to the Internet's first Duramax 6600 diesel discussion forum for the LB7, LLY, LBZ, LMM, LML, LGH & L5P RPO code engines. Tips on performance, fuel economy, troubleshooting and more.

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  #11  
Old 08-23-2010, 08:09 PM
T Hugo 22 T Hugo 22 is offline
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I had a similar problem with my '01 Duramax. It started going into limp mode pulling my 32' 5th wheel. That started Memorial weekend on my way back from an up north camping trip. I took it to a dealer and they diagnosed a P0093 code. After replacing the CP3 pump and fprv, it was still going into limp mode. It got to the point that it would go into limp mode just pulling up a slight hill, empty, not pulling a trailer. We checked the pickup screen in the fuel tank, and replaced a couple of fuel lines. It would still go into limp mode. My mechanic was stumped. I came across this thread and read the post by Kennedy. I e-mailed Kennedy. He suggested his ECM tune. He's only about an hour and a half from me so I drove up to have it re-tuned. On the way up, on a flat road, I pull out to pass a semi. I get right up beside him doing about 65, and it trips into limp mode. There I am, can't get enough speed to get by him and have to slow down and tuck back in behind him. I got the re-tune on 8/12. I could tell an immediate difference. More snap, very smooth. I've pulled my ATV all over the hills area south of Tomah, I've hauled a load of ties, and I've pulled my 5ver. It's running awesome, and it's pulling awesome. After I get a few more trips on it, I'll update with the results. But right now it's running better than it ever has. I'm glad I got my truck back. I couldn't stand not being able to get out and go, when I wanted to. Thanks Kennedy.
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  #12  
Old 08-27-2010, 09:52 AM
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More Power More Power is offline
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Thanks for posting your problem and apparent cure!

For those not well versed in what the diagnostic trouble code P0093 is, the book says "Fuel System Large Leak Detected (2001 model year)". The description doesn't tell the whole story or indicate what else may be causing the problem.

In short, this code indicates that the "commanded" and "actual" fuel rail pressures are outside a window of acceptability (the computer really has no way of knowing whether a leak exists). The ECM commands a particular rail pressure, depending on load, accelerator pedal position and other inputs, then commands the Fuel Pressure Regulator (FPR) and high-pressure pump to deliver that rail pressure. Ordinarily, the system will respond and generate those pressures.

There are a variety of causes of a P0093 trouble code, it could be that the injectors are worn and their internal clearances are allowing too much fuel to leak past the internal components of the injector(s). The FPR and high-pressure pump can't generate enough pressure/flow to compensate.

This code could also be the result of a faulty rail pressure relief valve, which leaks fuel pressure back into the fuel return line faster than it can be generated. The fuel pressure sensor could be at fault, as could the FPR or the high-pressure pump itself.

There is an injector fuel return test outlined in the service manual - using a set of four graduated cylinders, which are used to measure injector fuel return flow for one bank of injectors at a time. I doubt many dealer techs do this, but the test is available for those who want to confirm whether the injectors are the problem.

The window of acceptable pressures could also be so narrow that some trucks have a hard time staying within that narrow window of acceptable rail pressures. The 2001 trucks were the first to get a high-pressure fuel injection system like this. Variability in trucks, engines, fuel systems produce variability in setting codes.

We know that within the first year of production, GM widened the vehicle speed window when using cruise control because of driver complaints. I suspect there may be other areas of vehicle programming that needed some fine tuning as well. While we haven't heard the recommendation lately, during the first few years of Duramax production, GM recommended updating the ECM programming whenever the vehicle was returned to the dealer for service. I've had my 2001 ECM programming updated a couple of times. I wonder if maverick2's truck was recently updated by the dealership for this trouble code?

Always change your truck's fuel filter when a P0093 or any other rail pressure codes appear. Check your fuel tank cap for excessive vacuum. A faulty pressure/vacuum relief valve in the cap could add to the possibility of this trouble code. These diesel caps should vent at 2-psi positive pressure or 1" of vacuum.

Jim
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  #13  
Old 10-19-2010, 01:19 PM
Kennedy Kennedy is offline
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bump for reference
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2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
2005 Chev K3500SRW D/A CC Long LT(SOLD)
2007 Chev K2500 Classic EC Short LT (Sold)
2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
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  #14  
Old 06-21-2013, 01:30 PM
jde0330 jde0330 is offline
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Default FPRV Needed

Anyone know where to buy a fuel pressure relief valve? I've been searching the web and can't find one. I'd rather not shim the old one unless I have to.
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  #15  
Old 06-21-2013, 02:34 PM
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Quote:
Originally Posted by jde0330 View Post
Anyone know where to buy a fuel pressure relief valve? I've been searching the web and can't find one. I'd rather not shim the old one unless I have to.
Have you checked the relief valve for leakage? Kennedy has another recent post here that outlines how to perform the simple test for leakage.

Jim
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  #16  
Old 06-27-2013, 10:38 AM
Kennedy Kennedy is offline
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The LB7's do not typically leak or weaken. It's the LLY-LBZ-LMM that can be weakened IF they are beat up on by pressure cycling.

It's P0093 season and I am doing many 2001 LB7 ECM's with the same fix mentioned at the start of this thread.

Also seeing the same issue starting with LBZ and LMM P0087 codes.
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Kennedy Diesel-owner
More than just a salesman-I use and test the products that I sell on a daily basis!
Superflow Lie Detector in house
2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
2005 Chev K3500SRW D/A CC Long LT(SOLD)
2007 Chev K2500 Classic EC Short LT (Sold)
2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
2016 GMC K3500SRW D/A CC short LTZ

Custom tuning in house using EFI Live tuning software!
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  #17  
Old 10-22-2017, 02:58 PM
Seanlb7 Seanlb7 is offline
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Default Limp mode always on

I have a 2001 chevy 2500HD with the LB7 duramax, one day the check service engine soon light came on and thw truck wont excede 2000rpm, please let me know if the JK tune will fix this issue
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  #18  
Old 10-22-2017, 07:26 PM
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DmaxMaverick DmaxMaverick is offline
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Quote:
Originally Posted by Seanlb7 View Post
I have a 2001 chevy 2500HD with the LB7 duramax, one day the check service engine soon light came on and thw truck wont excede 2000rpm, please let me know if the JK tune will fix this issue
Welcome aboard!

Much depends on why. If the SES lamp is on, there are DTC's stored. You need to read the codes to find out why it limped. It may be a simple matter, or it could be serious. No knowing without the codes.
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  #19  
Old 10-23-2017, 07:57 AM
Kennedy Kennedy is offline
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Quote:
Originally Posted by Seanlb7 View Post
I have a 2001 chevy 2500HD with the LB7 duramax, one day the check service engine soon light came on and thw truck wont excede 2000rpm, please let me know if the JK tune will fix this issue
Quote:
Originally Posted by DmaxMaverick View Post
Welcome aboard!

Much depends on why. If the SES lamp is on, there are DTC's stored. You need to read the codes to find out why it limped. It may be a simple matter, or it could be serious. No knowing without the codes.

Yes check for DTC's. There may or may not be codes present. Having done this for many years now I with relate a few findings;

1) I have never seen the issue fixed with "parts"
2) I have had people claim to have spent as much as $9k chasing this only to be fixed with tuning
3) The tuning fix does not eliminate the need for fuel system upgrades (lift pump etc)

More reading:

http://www.kennedydiesel.com/docs/Du...20detected.htm
__________________
Kennedy Diesel-owner
More than just a salesman-I use and test the products that I sell on a daily basis!
Superflow Lie Detector in house
2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
2005 Chev K3500SRW D/A CC Long LT(SOLD)
2007 Chev K2500 Classic EC Short LT (Sold)
2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
2016 GMC K3500SRW D/A CC short LTZ

Custom tuning in house using EFI Live tuning software!
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