Question about 1998 GMC Sierra

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Missfire code po304 keeps comeing up cylinder 4 missfire detected after i changed the plug and wire I have the same problem initaly I replaced the plugs and wires and it helped a little so I did a compression test and it was fine. I then replaced the injetors and now my truck is reading a code for the MAP sensor throttle positon sensor. I just my truck to run right again it fells like it's falling on its face sometime but there is no consitancy sometimes warm sometimes cold. I would love to see point and vacume andvance come back there should only be three wires on the entire motor. OH to the good old days!!!

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  • jfisher1 Feb 11, 2009

    5.7L V8 and these trucks trucks have a single coil.

  • the dave May 11, 2010

    Where do you buy parts? What brands are the plugs, wires, and injectors?

  • wroberts20 May 11, 2010

    is this truck 6 or 8 cylinder. and do you have 1 coil pack or does each cylinder have its own?


5 Suggested Answers

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SOURCE: i have a 1996 safari

Disconnect battery for 30 seconds then reconnect that will reset code or it takes about 35 start cycles

Posted on Dec 02, 2008

  • 5 Answers

SOURCE: Miss fire code on computer

check fuel pressure regulator for bleeding.

Posted on Mar 22, 2009

  • 157 Answers

SOURCE: i have a 01 GMC sierra 4.3 and my check engine

chek injectors posible leak

Posted on Nov 04, 2009

  • 880 Answers

SOURCE: i have a 2000 gmc sierra 5.3 with a number 6

I would check the valves for number 6. If one or both are burned, stuck or out of adjustment it would cause your problem. If a cam lobe for that cylinder is burned or badly worn it could be the culprit.

Posted on Jan 10, 2010

  • 21949 Answers


wow you love spending money for nothing ,ask a local mechanic where the engine temperature sensor is located for the automatic choke and change it as i dont think its working correctly so mixture is weak hence the loss of power till engine warms up ,remember this vehicle is well past its sell by date so it may also pay to do a compression check as it could also be low on compression and its needs the valves grinding in and maybe new piston rings ,anothe pssibility is the head gasket it could be failing and blowing between two pistons and sealing up a bit when it warms up ?? who knows as their too many weird and wonderful faults with a motor vehicle .But i would go for the autochoke temperature sensor first where ever its located as iam a europeon mechanic and never seen this vehicle except on the TV so please forgive my ignorance of component location .

Posted on Sep 13, 2011

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