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I own a 2004 Z06

P0300 is a multiple misfire code. Every cylinder ends up misfiring. 7 and 8 misfire mostly at idle, every other cylinder misfires during driving.

My car has a Vararam intake system and OBX longtube with some highflow cats I had welded in in place of the stock resonators. At first I extended the O2 sensors myself, however I just recently place the O2 sensors back to stock and I am using LG 24 inch O2 extensions. The grounding connectors on the driver side of the block, and the rear part of the head are fine.

I have my own copy of Hptuners so I have been able to log information. The link below is to a logged file of a drive I did. I drove regular for a bit and then took it through one gear.

http://files.me.com/chrisrokc/4qp5z0

So far I have checked every spark plug wire and spark plug (TR5's). They are good. The spark plugs are white, which I don't like because I figure that indicates a lean condition. Picture of them is below. They are gapped at .057 ish.



Anyways, any help or information someone can give me would be helpful. This problem happens both with the stock tune, and a downloaded tune for longtubes off Hptuners.
 

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Your gap should only be at .040. Your current gap will have it running way too hot of a spark. Also, check your Wires with the engine running and the lights out. It will give you a chance to see any arcing that may be happening.
 

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Check the injector wiring harness where it wraps around behind the engine. There's a bracket there for the fuel rail that the wiring can rub against and eventually cut through and short out the injectors.

http://www.digitalcorvettes.com/forums/showpost.php?p=434808&postcount=9

Mine started as a miss (that's the p0300), but eventually the engine completely died. Now every time i think "miss" on a C5, i instantly think to look there first. Mine was very small and was not nearly as obvious as the one in those pictures.
 

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Discussion Starter #4 (Edited)
Your gap should only be at .040. Your current gap will have it running way too hot of a spark. Also, check your Wires with the engine running and the lights out. It will give you a chance to see any arcing that may be happening.
Thanks for the information guys. Hm, thats the way I had them gapped in the beginning, but then I read on z06vette to gap them higher. :thud:


I was able to check that wire when I was walking out the door this morning. It turns out that it has rubbed through the black wire wrapping for sure, I am not sure if it has made its way through any wires. This could be my problem! :thumbsup:

Will know more tonight.
 

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Ok, I am at home checking this out. I think it made its through the tape, but it is hard to tell because of where the harness is. Should I take off some of the tape? Or is there a better way? Also how did you guys fix the wires if they were damaged?
 

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Once it's gotten far enough to start causing a miss, then it's probably cut through the tape and through the insulation on the wire. It's shorting out the injectors on that bracket. Since it's a major pita to pull those wires out to fix it, i just covered the bracket with some rubber hose and and taped up the exposed area in the wires. I have a feeling it will cause more problems later down the road, but it works for now.
 

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Hi,

a guy here in Sweden had the same problem, it turned out to be a broken valve spring, the car was 2002 Z06.

Regards
MickeW
 
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