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Thread: 1973 GMC lt1

  1. #1

    Default 1973 GMC lt1

    Guys I have a problem that I have not been able to figure out. I had an 84 cutlass that someone had transplanted a lt1 out of a 94 caprice cop car in. They used the same wiring harness out of the caprice with the transplant. Motor ran great in that car. I knocked the transmission out of the car and pulled the motor and tranny and sold the car. I purchased a stand alone wiring kit from painless for that powertrain. I have a 1973 gmc 2wd truck that I decided to put the powertrain in. When I did so I did not use the original transmission, I just used the 400 turbo that was in the truck. I first used the same electric fuel pump that was in the cutlass. The truck starts idles and revs perfect, but when you go to drive seems like it's lacking a lot of power, and after running for approx 20 min engine would cut out and pop at around 4500rpm, the more you drive the truck the worse it gets, like a lack of fuel. It will never die but gets very doggy and hard to accelerate. But if you shut it off and go to restart it, it will fire for a split sec and die like a vapor lock. I thought it was a fuel issue so I hardlined my line to and from the tank all the way to the fuel rails and put on a bigger higher volumer fuel pump from holley. The motor has a constant 42lbs of pressure. The fuel pressure regulator appears to be working properly. I have put a new coil on the motor with no change. So I am out of idea's for now and hoping someone on here can help. I don't know if not running that 4l60e tranny will effect how the computer/engine performance if at all? It is the original computer out of the 94 caprice.

  2. #2


    The 4l60E is computer controlled, how did you compensate for the trans inputs to the computer?
    That could be the issue.

  3. #3


    I have not compensated for the inputs. Would i need to get my computer re-programmed to solve the input problem, or would I be best having the 4L60e rebuilt and put that in the truck?

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