Question about 1985 GMC C2500

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1985 gmc sierra shakes

I have a 1985 gmc sierra it was dumping gas and shaking bad i changed the spark plugs and adjusted the carb it is not dumping gas now but at take off it shakes and doesnt want to really go more the 5 miles and hour. any clue what can be wrong thanks

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  • Nicole Harmon Mallia Feb 26, 2009

    did all that it is good

  • Nicole Harmon Mallia Feb 26, 2009

    rechecked firing order and oil smells like oil. so where do i go from here???? thanks

  • Nicole Harmon Mallia Feb 26, 2009

    it is a holly 4 barrel

  • Nicole Harmon Mallia Feb 26, 2009

    i asssume dist is distributer. there is 3 wired that are unplugged by it and no wires that i know where they go any further direction would be great i am desperate for anyhelp that you may give tank you

  • Nicole Harmon Mallia Feb 26, 2009

    cant find the egr valve help please

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Sounds to me to be a timming issue like maybe retarted, also chk. to see if the wire is pluged in by dist, the wire that you have to unplug when your going to time it, i can't remember what its called. There is only 2 things on this truck thats controled by the computer is spark and fuel, if that wire is unpluged by dist. it will run like that, unless someone has changed it back to the old style dist. and carb. if thats the case loosen dist. and move it a little and see if it dosent run better, clockwise advance, counter clockwise is retarded.

Posted on Feb 26, 2009

  • ccn7 Feb 26, 2009

    What kind of carb. is on it a Qjet or an aftermarket like a holley or edelbrock or ?. Still sounds like a timming issue.

  • ccn7 Feb 27, 2009

    The egr valve is located either behind carb. or beside carb. bolted to intake with a vacume line going to it. Ok sounds like someone chg. the dist to the old style so don't pay any attention to the wires that are just hanging there. Did you do like i asked and try to move the distributer? at the base of dist. is a bolt that holds the dist. from moving loosen that bolt and turn it clockwise and see if it runs any better. If it runs worse turn it the other way counter clockwise and see how it runs. If you turn it both ways and it makes no differance than it could be the egr valve.

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Nic, If the carburetor was dumping gas, remove the engine oil dip stick and see if it smells like gasoline. If it does you will need to change the oil.
Second, go back over your spark plug wires and verify they are on the correct spark plug. Start with the #1 plug wire, the firing order is 1,8,4.3.6.5.7.2...
Let me know how it turns out and we can go from there.
Good luck.

Posted on Feb 26, 2009

  • Bruce Bracey
    Bruce Bracey Feb 26, 2009

    Nic, I would check the EGR valve next. When the engine is cool, place your fingers under the metal top until you feel the diaphram. Squeeze and move the diaphram up and down. It should move freely. Next, remove the vacuum hose and see if the engine runs better.

    Let me know.

    Regards,

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