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problems with 91 3500 7.4L

Discussion in 'Chevy Trucks' started by CSC Contracting, Nov 20, 2010.

  1. CSC Contracting

    CSC Contracting Senior Member
    Messages: 105

    I need some help. My 91 k3500 with the 7.4L
    1st The tack jumps 100-200 rpms like a miss at all speeds and idle.
    2nd I get a small bakefire through carb if I jump on it
    3rd yesterday I was sitting at a light and truck started to surge like my foot was on the gas and brake..

    Thanks for any help
  2. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    91 doesnt have a carb, but was throttle body injection (looks a little like a carb). I've seen 454s in the 90s era with vacuum leaks and intake leaks, which would cause what you are describing. You can try spraying alittle wd40 or similar petroleum based spray around the intake area while it's running, to see if you can find the leak. Once you pin it down you'll know if it's something simple like a cracked vacuum line, or an actual manifold leak.
    Good luck