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So I’ve been trying to chase down this weird misfire issue. I bought a wrecked c6 to rebuild and from the start it would misfire VERY little at idle, unnoticeable if you aren’t familiar with working on cars. Under WOT it was super noticeable and would go then misfire then go then misfire. Just breaking up during WOT. Revving the car in park showed nothing just a smooth rev.
Since then I’ve replaced, MAF, Both primary o2, All plugs and plug wires. Still has funky slight misfire at idle.
I haven’t had a chance to drive it yet as it’s getting fixed but still throwing P0300 if I sit there and idle and rev it a lot. I checked GM pids for misfires and it shows all 8 are misfiring intermittently.
The images attached on the left shows current misfires during revving/idle and on the right anything besides a 0 shows misfire counts/history since starting car.
Damaged reluctor wheel? Bad throttle body/throttle position sensor?
I mean car cranks fine and revs fine so I doubt any of those two are bad. I’d think I’d get a code for a tps sensor or even a crank position sensor code
Coils getting proper voltage? Since a coil will produce a weak spark with low input voltage that's a possibility also a possibility that you have time timing off slightly or you have bad coils.
Coils getting proper voltage? Since a coil will produce a weak spark with low input voltage that's a possibility also a possibility that you have time timing off slightly or you have bad coils.
How would I go ahead and check for proper voltage on the packs? Battery is only a year old so that shouldn’t be the issue.
I was getting a P0300 code on mine randomly for a year and could never find the issue. Using my VCX Nano I was getting misfires like you posted. One day when pulling into a parking lot, something happened and the engine started running on like 6 cylinders and threw a check engine light. It finally threw a code for the crank position sensor. I limped it home and changed out the crank sensor. In now runs better than it ever did and have not had the P0300 code since. You may want to try just changing the crank sensor.
I was getting a P0300 code on mine randomly for a year and could never find the issue. Using my VCX Nano I was getting misfires like you posted. One day when pulling into a parking lot, something happened and the engine started running on like 6 cylinders and threw a check engine light. It finally threw a code for the crank position sensor. I limped it home and changed out the crank sensor. In now runs better than it ever did and have not had the P0300 code since. You may want to try just changing the crank sensor.
Figured I should do that, car has 100k miles so definitely should be done by now.
I was getting a P0300 code on mine randomly for a year and could never find the issue. Using my VCX Nano I was getting misfires like you posted. One day when pulling into a parking lot, something happened and the engine started running on like 6 cylinders and threw a check engine light. It finally threw a code for the crank position sensor. I limped it home and changed out the crank sensor. In now runs better than it ever did and have not had the P0300 code since. You may want to try just changing the crank sensor.
Well just my luck ahah, I replaced it and it didn't work. I don't know if I have to relearn the crank sensor after replacing it. I get my VCX nano in soon so should I try a relearn? It still misfires a lot when coming back to an idle after revving it.
Well, it was worth a shot, sorry it didn't help you. I did the relearn and then erased all the codes on mine. If yours is still misfiring, I don't think a relearn will fix that.
Have you pulled the valve covers to look for broken springs?
I have pulled the covers to do gaskets and took a look around but not really in-depth but I didn't see anything wrong with it. I wouldn't think 8 cylinders would have broken springs ahaah. I did another log for misfires just now and its even worse when replacing the sensor. I have a hard feeling that I need to do a relearn and maybe it will fix it. Crossing my fingers
My son's Avalon was doing this. We found out it had one bad coil. But it was setting the P0300 and all 6 cylinder misfires.
I reset the code and got "B" coil fault.
We exchanged that coil with the "D" coil and the fault moved to "D".
One bad coil was causing it to set all 6 misfire faults.
He replaced it. And he drove from Indinapolis to Michigan last weekend with no problems at all.
Thank you all for the replies, I still have been waiting on the car to get back from frame repair for about 3 months now so ill try your suggestions about the battery and such. I really don't think the battery is causing it but in case I bought a tester to have since I always needed one. My theory is it's probably a ground issue.
07-08-2022, 06:00 PM
Misfire on all 8 Cylinders and P0300 Code
