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Duramax 6600 Discussion Forum for the Duramax 6600 Diesel Engine, including the LB7, LLY, LBZ & LMM engine specific topics.

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  #1  
Old 04-09-2010, 12:46 PM
maverick2 maverick2 is offline
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Default 2001 LB7 fuel system/limp mode problem SOLVED

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/t...ad.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.
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  #2  
Old 04-09-2010, 03:52 PM
NutNbutGMC
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Quote:
Originally Posted by maverick2 View Post
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/t...ad.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.
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  #3  
Old 04-10-2010, 08:05 AM
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Mark Rinker Mark Rinker is offline
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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?
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  • Total GM diesel miles to date : ~950K
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  #4  
Old 04-10-2010, 10:40 AM
maverick2 maverick2 is offline
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Quote:
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.
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  #5  
Old 04-10-2010, 05:30 PM
NutNbutGMC
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Quote:
Originally Posted by maverick2 View Post
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.
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  #6  
Old 04-13-2010, 10:14 AM
madmatt madmatt is offline
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Quote:
Originally Posted by Mark Rinker View Post
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??
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  #7  
Old 04-13-2010, 07:34 PM
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Mark Rinker Mark Rinker is offline
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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.
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2005 GMC Yukon Denali 6.0L gas (hey its paid for)
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW
  • Total GM diesel miles to date : ~950K
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  #8  
Old 04-13-2010, 08:11 PM
madmatt madmatt is offline
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thanks and i hope no one thinks i was trying to stir the pot,, i was just wondering whats tunes he could compare too.
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  #9  
Old 05-16-2010, 11:06 AM
maverick2 maverick2 is offline
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Default Update

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.)
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  #10  
Old 07-21-2010, 02:46 PM
Kennedy Kennedy is offline
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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.
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