2001 LB7 fuel system/limp mode problem SOLVED

[maverick2]

A couple weeks I came on this board looking for help in diagnosing our ’01 Duramax – the pickup would go into limp mode pulling a trailer up a long grade and record the “P0093A” code in storage.

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=36637

General consensus among local mechanics (GM and others) was that the pickup probably needed new injectors based on its age, mileage, error code, and the general reputation of the LB7. That didn’t make sense to me, as the pickup exhibited NONE of the performance traits of faulty injectors, so I decided to look for help here before going any further. Among the people replying was John Kennedy. Following a few phone calls and e-mails, I decided to follow John’s advice and swap out the original ECM with one of his “tuned” ECMs, as he had a very logical explanation as to what was happening, why, and how he corrects it with his re-programmed ECMs. We installed one of his ECMs yesterday, and after steep grade test drives w/ and w/o a trailer in tow, I believe my problem is solved. Will continue to test and look for signs of physical fuel system problems over the next couple weeks under varying conditions, but initial indications are great:

1. Operating under load with the scan tool attached, my mechanic could immediately see that “actual” fuel pressure tracked very closely with the “desired” fuel pressure using John’s re-programmed ECM. The difference between those 2 values (and the lag in response) was very notable with the original ECM and seemed to be what was triggering the “limp mode”.
2. All attempts to force the pickup to go into limp mode (by repeatedly re-creating the same conditions that caused it previously) all failed. Prior to swapping ECMs, the pickup would go into limp mode quite readily as long as we had our gooseneck trailer in tow. After swapping ECMs, I ran a 5-mile grade quite aggressively w/ the trailer in tow, and it didn’t miss a beat.

Will update my findings again in a few weeks after I’ve got more miles on this ECM, but I strongly suspect Kennedy Diesel has the ’01 Duramax “phantom limp mode” figured out. To anyone faced with a similar situation, I’d suggest at least a call to John prior to going thru a spendy injector replacement.

[NutNbutGMC]

A couple weeks I came on this board looking for help in diagnosing our ’01 Duramax – the pickup would go into limp mode pulling a trailer up a long grade and record the “P0093A” code in storage.

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=36637

General consensus among local mechanics (GM and others) was that the pickup probably needed new injectors based on its age, mileage, error code, and the general reputation of the LB7. That didn’t make sense to me, as the pickup exhibited NONE of the performance traits of faulty injectors, so I decided to look for help here before going any further. Among the people replying was John Kennedy. Following a few phone calls and e-mails, I decided to follow John’s advice and swap out the original ECM with one of his “tuned” ECMs, as he had a very logical explanation as to what was happening, why, and how he corrects it with his re-programmed ECMs. We installed one of his ECMs yesterday, and after steep grade test drives w/ and w/o a trailer in tow, I believe my problem is solved. Will continue to test and look for signs of physical fuel system problems over the next couple weeks under varying conditions, but initial indications are great:

1. Operating under load with the scan tool attached, my mechanic could immediately see that “actual” fuel pressure tracked very closely with the “desired” fuel pressure using John’s re-programmed ECM. The difference between those 2 values (and the lag in response) was very notable with the original ECM and seemed to be what was triggering the “limp mode”.
2. All attempts to force the pickup to go into limp mode (by repeatedly re-creating the same conditions that caused it previously) all failed. Prior to swapping ECMs, the pickup would go into limp mode quite readily as long as we had our gooseneck trailer in tow. After swapping ECMs, I ran a 5-mile grade quite aggressively w/ the trailer in tow, and it didn’t miss a beat.

Will update my findings again in a few weeks after I’ve got more miles on this ECM, but I strongly suspect Kennedy Diesel has the ’01 Duramax “phantom limp mode” figured out. To anyone faced with a similar situation, I’d suggest at least a call to John prior to going thru a spendy injector replacement. Interesting and thanks for sharing. I am glad to see you may have cleared a hurdle without new injectors.

[Mark Rinker]

I have said many times on TDP that Kennedy has the best LB7 tune out there. GM would have been well advised to license his tune, and put it on every 2001-2004.5 truck that rolled out the doors. Watch the color of your crankcase oil, over the next few changes. By change two or three, you start to see less soot, and the oil might even stay honey colored awhile, instead of instantly black.

My 2002 K2500 was still running smooth and had honey colored oil at 285K when I sold it, with JK's tune intact. It was so right for that truck, I couldn't bear to put the old factory tune in it!!!

Have fun...happy hauling. Q: Did you buy his boost-valve to bring up boost slightly for the increased fuel rate?

[maverick2]

Q: Did you buy his boost-valve to bring up boost slightly for the increased fuel rate?
No -- all efforts to date have focused on fixing the phantom limp mode problem. Available power and torque has never been an issue with this particular pickup, so haven't looked into any enhancements there. The bump in Hp with the Kennedy's base tune in the ECM I received is noticeable though and kinda fun.

[NutNbutGMC]

No -- all efforts to date have focused on fixing the phantom limp mode problem. Available power and torque has never been an issue with this particular pickup, so haven't looked into any enhancements there. The bump in Hp with the Kennedy's base tune in the ECM I received is noticeable though and kinda fun.
I had a 2001 LB7 and ran it for ~ 50K miles. That engine would flat get it. I didn't realize it until I traded it off for a 2002 crew cab. That (2002) particular LB7 was weaker and nothing but an injector destroyer.

I ditched it for a 2007 and the LBZ is turned up a bit (HP) but I havent driven it much since I bought it new in July 2007.

[madmatt]

I have said many times on TDP that Kennedy has the best LB7 tune out there. GM would have been well advised to license his tune, and put it on every 2001-2004.5 truck that rolled out the doors.

PLEASE, no one take this the wrong way, but what other EFI Live tuners have you tried??

[Mark Rinker]

None - my LB7 comparisons were made to stock OEM settings, a couple generations of Diablosport (Predator) tunes/levels, and HyperTech. Also drove a couple friends trucks with FRP boxes, Edge Products, and ran MSD's propane injection stacked with the tunes on my truck as well.

Kennedy's switchable tow/'haul ass' LB7 tune was the smoothest, quietest, and most powerful of my experience.

I am certain there are other great EFI-Live tunes out there, but if you find the sweet spot of any motor, then you found it. It can be duplicated, but not easily improved upon.

[madmatt]

thanks and i hope no one thinks i was trying to stir the pot,, i was just wondering whats tunes he could compare too.

[maverick2]

I now have a couple thousand miles on this rig with the new ECM, and it's running flawlessly. 2/3 of those miles have been while pulling a gooseneck horse trailer, and we've yet to encounter the dreaded "limp mode". Very pleased with Kennedy's re-tuned ECM from that aspect, and his wealth of knowledge on the Duramax in general. I'm guessing I saved $2500 worth of new injectors (which may not have fixed my problem.)

[Kennedy]

Since doing Mark's I have done several others with great success in all but one. This particular truck is a repo and is new to the owner. It has other issues that need to be checked out. Thankfully it's nearby in Southern WI.

I've also fielded numerous calls and spent a lot of time explaining the situation. My hope is to get some further documentation worked up so I can refer to testimonials, etc and spend less time explaining the same thing over and over again. I hope to work up some details soon.

[T Hugo 22]

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.

[More Power]

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

[Kennedy]

bump for reference

[jde0330]

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.

[More Power]

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

[Kennedy]

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.

[Seanlb7]

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

[DmaxMaverick]

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.

[Kennedy]

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.


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/Duramax%20LB7%202001%20DTC%20P0093%20Large%20fuel% 20leak%20detected.htm