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Thread: GMPP LS376/525 crate motor and ECU going into limp mode

  1. #1

    GMPP LS376/525 crate motor and ECU going into limp mode

    Got a mixed bag going on. 2003 corvette z06, motor blew, owner decided to put a GMPP LS376 and standalone computer into it. No codes popping up on either ECU but the pedal goes dead after you try to drive it. Driving it around under very light throttle is fine but anything over say 25% throttle it goes into limp/reduced power and the pedal is not responsive. From what I gather the coolant/tach/vss from the new ecu is spliced into the old ecu. Its got the factory ecu under the fender and a new ecu up front. When it goes into limp mode, the pedal will not work and no codes pop up.
    Phil
    1999 Corvette Coupe
    Worlds Fastest 346" N/A Coupe
    ProStreet Motorsports
    HP Tuner SD specialist All GM Vehicles
    2000 Mustang 438" LSx 4.70 @ 164
    ------
    NEW 346" N/A testing: 10.4 @ 132.4 N/A(875')
    NHRA Corrected: 10.21 @ 134 N/A
    Old Nitrous Best: 10.0 @ 138.89(181 DA)

  2. #2
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    I'm having the SAME exact problem, literally identical, in a GMPP crate LS7 swapped into an older C4. Let me know if you figure out the problem, and I'll do the same for you if I find it first.

  3. #3
    Quote Originally Posted by That_guy View Post
    I'm having the SAME exact problem, literally identical, in a GMPP crate LS7 swapped into an older C4. Let me know if you figure out the problem, and I'll do the same for you if I find it first.
    Whats weird is its supposed to be tuned but upon startup, the ECU was adding 30% fuel. I threw my wideband on it and it showed 21:1 A/F. I added 30% fuel to the MAF and now it idles around 14.5:1. I am starting to wonder if the ECU is just a generic tune that needs to be tweaked.
    Phil
    1999 Corvette Coupe
    Worlds Fastest 346" N/A Coupe
    ProStreet Motorsports
    HP Tuner SD specialist All GM Vehicles
    2000 Mustang 438" LSx 4.70 @ 164
    ------
    NEW 346" N/A testing: 10.4 @ 132.4 N/A(875')
    NHRA Corrected: 10.21 @ 134 N/A
    Old Nitrous Best: 10.0 @ 138.89(181 DA)

  4. #4
    Quote Originally Posted by That_guy View Post
    I'm having the SAME exact problem, literally identical, in a GMPP crate LS7 swapped into an older C4. Let me know if you figure out the problem, and I'll do the same for you if I find it first.
    I talked to a a buddy who has done a bunch of these motors and he said the only problem he ran into was when the MAF was not in a 4" tube or when the MAF was really close to the TB. He said make sure its at least 12" from the TB and in a 4" tube. Apparently the air flow gets dirty that close and disrupts the MAF signal. Going to try that first and if that doesn't work, we are going to pull all the extra PCM and let the factory PCM run the whole combo.
    Phil
    1999 Corvette Coupe
    Worlds Fastest 346" N/A Coupe
    ProStreet Motorsports
    HP Tuner SD specialist All GM Vehicles
    2000 Mustang 438" LSx 4.70 @ 164
    ------
    NEW 346" N/A testing: 10.4 @ 132.4 N/A(875')
    NHRA Corrected: 10.21 @ 134 N/A
    Old Nitrous Best: 10.0 @ 138.89(181 DA)

  5. #5
    Advanced Tuner
    Join Date
    Mar 2009
    Location
    Earth
    Posts
    213
    Quote Originally Posted by Phil99vette View Post
    I talked to a a buddy who has done a bunch of these motors and he said the only problem he ran into was when the MAF was not in a 4" tube or when the MAF was really close to the TB. He said make sure its at least 12" from the TB and in a 4" tube. Apparently the air flow gets dirty that close and disrupts the MAF signal. Going to try that first and if that doesn't work, we are going to pull all the extra PCM and let the factory PCM run the whole combo.
    I would think you could just scale the MAF and clean up a bunch of that. I absolutely do HATE some of these intake setups on the Corvettes that put the MAF literally right in front of the TB, but most of the time I can get the car to run ok unless it's got a big cam in it.

    I think I remember reading somewhere that the GMPP crate engines had faulty PCM issues with some of them. I wonder if that's our problem?