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Bad misfire

Bad misfire

Postby 03z71 [OP] » Nov 20 2011, 9:45pm

I have a 2003 GMC sierra 1500 with the 5.3 in it. I put new spark plugs and wires in it not to long ago and it has a terrible misfire at idle. Many ideas on what could cause this? like i said i already changed the wires and plugs and it did not help.
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Re: Bad misfire

Postby StarsnBars » Nov 20 2011, 9:55pm

Was the misfire there before you changed the plugs and wires? If after, you might have a cracked spark plug.
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Re: Bad misfire

Postby 03z71 [OP] » Nov 20 2011, 10:16pm

Been the same before and after
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Re: Bad misfire

Postby country1911 » Nov 20 2011, 11:51pm

Specific cylinder? Any codes? Could be a coil pack or intake gaskets or plugged cats or... You get the point.
To check for bad intake gaskets, spray some carb cleaner around them with the engine running. If it sputters, they need replacement.

If it is one cylinder, try switching the coilpack with another one. If the problem follows, it is your problem.

Good luck
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Re: Bad misfire

Postby 03z71 [OP] » Nov 21 2011, 2:21am

Could the mafs have anything to do with it?
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Re: Bad misfire

Postby country1911 » Nov 21 2011, 3:09am

Could, kind of helps to know what codes there are. Go to autozone and get it read, its free.

Could be a plugged air filter, bad plugs, bad spark plug wires, bad cylinder head, head gasket... I can go on all night. We really need more info from you first.
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Re: Bad misfire

Postby Gorecki » Nov 21 2011, 3:11am

Last time I saw this it was a leaky/failing fuel injector. Not saying it is the case for you but the symptom was the same.
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Re: Bad misfire

Postby 03z71 [OP] » Nov 21 2011, 3:35am

Sorry about not saying much about it. Its always had a little miss fire but here recently its gotten worse. The truck came with headers. And now it has new shorty headers, new k&n air intake, new jet flow mafs, and new throttle body spacer, all new plugs and all new spark plug wires. Some people have told me that it might be the air intake and headers messing up the computer with the extra air flow. I pluged up my programmer and it gave me one dtc (Po101) which is mafs. So I put my stock mafs back in and it took away a lot of the misfire but it still has a slight misfire. I also hooked up a computer to it and its said the misfire is coming from cilinder 2 and 7. Hope that helps some. Thanks for all your replys.
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Re: Bad misfire

Postby country1911 » Nov 21 2011, 4:05am

A plugged cat or bad intake gaskets will also lead to a maf code and misfires. Try the carb cleaner test and report back.
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Re: Bad misfire

Postby country1911 » Nov 21 2011, 4:18am

Another thing, check to be sure your intake tube is tight and sealed. A leak there may give you some of these same symptoms.
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