1991 2500 gmc running to rich

Discussion in 'GMC Truck Forum' started by modracer, Apr 26, 2010.

  1. modracer

    modracer Member

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    hi

    my buddys got a 1991 2500 gmc with the 5.7 350 in it. the truck right now runs like a peice of **** its running way to rich, in order to start it you have to hold it to the floor and it will take a few seconds to rev up and it will only run right high rpm's between 3000 rpms and 4000 i know thats kinda high to be reving it but its the only way it will run any thing below that it sputters and just blows out black smoke. we have tryed new plugs, wires, cap, new coil, just little stuff. i noticed when you crank it over not touching the trottle it sprays alot of fule in to it then you give it trottle and it just becomes like this little spray. i dont know to much about the whole tbi system so anyone who can help me out that would be great.

    thanks
     
  2. silverhairdeere

    silverhairdeere Senior Member

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    i would say your injectors are really gummed up , or your fuel pressure is really high , try some seafoam in the gas tank first , and post back to us .
     
  3. fordson

    fordson Senior Member

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    have you checked for codes is check engine light on something is calling for fuel when it should not be sometimes on these early models you can take the battery cables off for about 15 minutes put them back start it up allow a few minutes for the computer to reset and it's allright if that don't work you need to hook it up to a scanner other wize you can spend alot of money and still have your problem.
     
  4. Towtruck

    Towtruck Senior Member

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    Check the fuel pressure regulator that is built into the TBI they are known to go bad and dump to much fuel into the engine. There should be a rebuild kit for the regulator at your local auto parts store
     
  5. Oldmech

    Oldmech Full Member

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    sounds like you have a temp sensor teling your computer that its -35 and the tbi is dumping extra fuel to compensate
     
  6. modracer

    modracer Member

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    where abouts is this temp sencor?

    thanks kyle.m
     
  7. Oldmech

    Oldmech Full Member

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    I believe it is in the coolant passage at the front of the manifold near the water neck. if it is bad it will do exactly what your talking about.
     
  8. tjrettig44

    tjrettig44 Full Member

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    I had the same problem on my 91 Gmc Sierra I ended up replacing the Throttle Positions Sensor(TPS) and it fixed mt problem!
     

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