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My 96 GMC sierra has a random misfire

I recently did a tune up on my 96 GMC sierra with a 5.7 vortec engine. I replaced the spark plugs and wires. The truck was running fine before but now it has a random misfire. The diagnostic I did gave me a P0300 code for a random misfire and something to do with my mass air flow censor being faulty. I replaced the censor and erased the codes on my computer as well as resetting it and it still runs like ****. Could I have a bad distributor or a bad connection somewhere? Why would my engine be running like this now and not doing it before? Anyone have a suggestion?

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  • mossimo Nov 10, 2008

    Same thing has happened on my '96 GMC, 5.7 Vortec. New plugs, new wires and now the P0300 code keeps coming up. It's worse at freeway speeds on level road. If I accelerate or slow down I don't feel any misfire. I've checked for vacuum leaks. Recently replaced the intake manifold gasket. Engine has about 125k miles.

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Couple of things, did you actually gap the plugs yourselfor did you go on the assumption that they are pre gapped ? are the lead wires all in the correct firing order ? Is it possible a vacuum line got dis-connected ? I would also check the cap and the rotor.

Posted on Oct 27, 2008

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