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Thread: 2001 LB7 fuel system/limp mode problem SOLVED

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  1. #1
    Join Date
    Aug 2008
    Posts
    18

    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.

  2. #2
    NutNbutGMC Guest

    Default

    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.

  3. #3

    Default

    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?
    2011 Chevrolet Tahoe 5.3L daily driver
    • 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, '05 Denali
    • Total GM diesel miles to date : ~950K

  4. #4
    Join Date
    Aug 2008
    Posts
    18

    Default

    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.

  5. #5
    NutNbutGMC Guest

    Default

    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.

  6. #6
    Join Date
    Jan 2005
    Location
    Southern Indiana
    Posts
    1,177

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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??

  7. #7

    Default

    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.
    2011 Chevrolet Tahoe 5.3L daily driver
    • 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, '05 Denali
    • Total GM diesel miles to date : ~950K

  8. #8
    Join Date
    Jan 2005
    Location
    Southern Indiana
    Posts
    1,177

    Default

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

  9. #9
    Join Date
    Oct 2017
    Location
    sarasota
    Posts
    1

    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

  10. #10
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

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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.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  11. #11
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    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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