98 jimmy 4.3L loss of power when Wide Open Throttle

Discussion in 'Chevy Blazer Forum (GMC Jimmy)' started by 88Sierra, Aug 10, 2014.

  1. 88Sierra

    88Sierra New Member

    hello every body, I have a 98 GMC jimmy with a 4.3L 4x4, it has been a great truck with a few problems here and there. So the issue I am having is that over 40MPH if I try and go wide open throttle it will backfire and start misfiring until you let off the throttle. When going up hills it struggles really bad, wont go over 50mph and that's all the way floored. I hooked my scanner up to it and the only code it has is a p0420, but that is because there is no Catalytic converter on the vehicle. The air/fuel ratio at idle and up to 40 MPH is 14.0:1, when it starts to misfire and have loss of power air/fuel ratio will drop to 12.0:1.
    From a dead stop can I open it up to Wide Open Throttle and it will break the tire loose and accelerate perfectly fine up until after 40 Mph. I have changed, plugs, mass airflow sensor(separate problem when I firs bought the vehicle), checked timing on distributor(set to TDC and matched rotor to #6 cylinder was fine), cleaned throttle body an fuel filter. If anyone has any suggestions I am open to anything this problem is getting really annoying and don't know what else to look at.
    Thanks for your time
  2. 88Sierra

    88Sierra New Member

    Anyone have any ideas, I would appreciate it!
  3. BurbanMan

    BurbanMan Rockstar 3 Years 500 Posts

    Sounds like you distributor gear took a dump. Remove the dizzy and examine the gear on the end. They are notorious for going bad. Dorman makes one out of a stronger alloy that you can purchase at oreilly's. My wifes went bad and threw NO check engine light codes.
  4. 88Sierra

    88Sierra New Member

    Thank you burban man, that actually crossed my mind a bit I will be pulling it this week to check it out. Will the gear be rounded on the ends or what's will help me tell it may be bad? Thank you for the help
  5. BurbanMan

    BurbanMan Rockstar 3 Years 500 Posts

    It may be rounded. The one in our tahoe was chipped and looked similar to a worn limited slip diff setup
  6. Crispyt

    Crispyt Rockstar 100 Posts

    You could try just popping the distributor cap off and see if theres a lot of play in it but moving the rotor back and forth. If there's a lot of play you will notice it there. Also make sure that you have the delco spark plugs in it, anything else will make the votec motors unhappy and cause weird missfires. Could also be a vacuume issuse at the map sensor. I think those fit in a rubber grommet on the intake manifold. Ive seen the grommets go bad and it will suck air there and cause a bad reading at the sensor.

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