Voodoo13

After installing headers on the weekend I took the car for a drive today. It runs terrible. I can hear it popping, burning gases in the exhaust? and I have a
P0300 code
no other codes.

Checked all plug wires, they are all connected, pushed in till they "click"New plugs, NGK TR51X Irridium, New Wires, NGK.

Here is the O2 sensor data. Can a bad O2 sensor cause a random misfire code?



Also forgot to add, 2003 C5 Vert, Stock until now.

ssrallyred

The only 2 that really matter as far as this discussion in that you have only driven it a very short time would be the B1-S1 & B2-S1. if the battery was disconnected ignore the fuel trim readings at this point. But my hunch is that the 02's are in no way the problem with it running "terrible" You could take it off the rack after installing the headers and IF all else was OK it would run fine on an initial test drive for a few miles no problem with the 02's not even hooked up. Look else where. Matter of fact I would check for a broken/cracked spark plug first.

Voodoo13

Yes, the battery was disconnected, and what you say makes more sense to me considering the code. I was looking at B2 S1, thinking that it was not sensing properly. From what you say I'll stop looking at fuel and start looking at the ignition side again. Hopefully tomorrow.

Thanks for the input.

Voodoo13

Thank you so much SSRALLYRED. You were bang on with that diagnosis. Here is the proof in pictures. I changed the plugs before I went to work this morning and it runs just as good as before. I think I am going to fire that mechanic who did this I still have some concerns about the O2 sensors, It seems as if it just doesn't have any response, even after driving about 30 miles.



Here is the new O2 sensor graph. after the 30 mile drive on the highway. Any ideas anyone? Is it toast?

ssrallyred

Congrats my friend ! Was the cracked plug on the passenger side by chance ? the reason I ask is the 02 sensor on that side was receiving lots of unburned fuel from the misfiring cylinder. Don't give up on it yet as it very well might "get better". Happy I could help. I am in the business of repairing cars but I still pick up things here !

Voodoo13

I thought the same, and just changed the plugs on the right, they were all good. Drove it 2 miles and it was still the same. Then changed #1 plug and it was cracked - replaced and drove it with the same problem. I persevered and changed them all, I was never so happy to find that #8 was cracked too.

I'll drive it another week and take another O2 reading. If it is flat still I don't mind changing them out. Just want it running as best as it can before taking it for a dyno tune. Keep ya posted on what I find just to close the loop on this one.

ssrallyred

Thanks look forward to it ! Once you get that done get a tune and enjoy!

jcgunn

Gotta' love this forum!! One brother just saved another brother a whole lot of time and trouble and CA$H!!