P0300 Random Missfire - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 7 (permalink) Old 08-24-2010, 10:25 PM Thread Starter
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Question P0300 Random Missfire

Well like it says.... I have a random misfire. I took it in to my buddies shop and we hooked it up to his diagnostic machine and it is picking up a missfire on all cylinders at an idle. At an idle you can tell but once I get over 1500 rpm it seems to go away but the reader it telling us that shes still misfiring. We did a vacume leak test and a compression test and everything looks good. So im looking for some ideas. Can one bad injector cause a random misfire accross the board???


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post #2 of 7 (permalink) Old 08-24-2010, 11:05 PM
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Quote:
Originally Posted by dkscbalt View Post
Well like it says.... I have a random misfire. I took it in to my buddies shop and we hooked it up to his diagnostic machine and it is picking up a missfire on all cylinders at an idle. At an idle you can tell but once I get over 1500 rpm it seems to go away but the reader it telling us that shes still misfiring. We did a vacume leak test and a compression test and everything looks good. So im looking for some ideas. Can one bad injector cause a random misfire accross the board???
dude yes it can, my car is in the shop for that problem. change your spark plugs then see wat happens from there

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post #3 of 7 (permalink) Old 08-25-2010, 02:08 AM Thread Starter
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Yea I changed the plugs and had the same results. Im either thinking its a bad injector or possibly a burnt out valve. If thats the case I get to do the port and polish that Ive been talking bout for such a long time. I have also read that there can be a bad ground on our motors " the 2.2" that can cause this. I have also heard it cold be my CIA but I highly doubt that. I won a set of injectors on EBAY for 55 dollars so Im hoping that will fix the misfire at idle problem. I will keep you guys posted on what I find out. Im also still open to being pointed in the direction that could be causing this headache as Im picky and dont like my babys CEL on.


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post #4 of 7 (permalink) Old 08-25-2010, 09:56 AM
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keep me updated then

R.I.P. :(

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post #5 of 7 (permalink) Old 08-25-2010, 12:55 PM
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What do you have you spark plugs gapped at? I would say that may be causing it, however I find it hard to believe that your car is blowing out the spark, exhaust mods again?

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post #6 of 7 (permalink) Old 08-25-2010, 09:10 PM Thread Starter
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No the exhaust is something I have not changed yet.... Still running my Tsudo cat back, and OBX header downpipe from Ebay. I will be changing that soon though. The only other thing that crossed my mind was I put the Injen Hydroshield on my CAI. Not sure if that is causing it though. Weird thing is that my CEL hasnt come on in the past day. I have narrowed it down to the misfire throwing the code only at idle rmps. I can feel the misfires also when im paying attention. I guess the solid motor mounts are paying off lol. Im gonna check my valves at my buddies shop when I change my injectors. Just wanna make sure I dont have a burnt exhaust valve.

---------- Post added at 08:10 PM ---------- Previous post was at 08:07 PM ----------

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No the exhaust is something I have not changed yet.... Still running my Tsudo cat back, and OBX header downpipe from Ebay. I will be changing that soon though. The only other thing that crossed my mind was I put the Injen Hydroshield on my CAI. Not sure if that is causing it though. Weird thing is that my CEL hasnt come on in the past day. I have narrowed it down to the misfire throwing the code only at idle rmps. I can feel the misfires also when im paying attention. I guess the solid motor mounts are paying off lol. Im gonna check my valves at my buddies shop when I change my injectors. Just wanna make sure I dont have a burnt exhaust valve.
Oh yea the plug gaps are all at .040. I also ordered a set of Denso Iridiums. They are supposed to be the best plug for the 2.2 Ecotec N/A application.


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post #7 of 7 (permalink) Old 08-29-2010, 11:07 AM Thread Starter
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Well I changed my injectors and the misfire code is gone and my balt is running great! I wish I took a pic of what came outta my fuel rail though. I think its time to change my fuel filter. Kinda strange though my car only has 45,000 miles.


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