Misfire, running rich
06-28-2012, 08:11 PM
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Misfire, running rich The story: Car was running great. I parked it outside overnight. The weather was warm and dry, but I did have the ac on before i parked it so moisture could have caused an issue. I started it the next morning and as soon as I started to drive away it was running like ****.
Symptoms:
p0300 - Random/Multiple Misfires
Rough idle
Very rough under slight load at low rpms (shakes shifter all over when releasing clutch from stop)
Weak top end and rough low end, still pulls strong in the 3,000 - 4,000 RPM range
Smells rich, there's a fuel smell when cold and once the cats heat up it smells like a freakin skunk
Backfires out exhaust under load at low rpms.
SES light blinks under load and sometimes at idle, stays solid most of the time.
I have a cheap scantool that i was able to read some of the sensors with, but I was not able to read misfire counts on each cylinder. Both front O2s look to be reading fine, but the fuel trims look weird. Bank 1 long term bounces from 0 to 12%, which isn't great, but bank2 LTFT goes from 10 to 25%. Both short term trims bounce between +- 12%. Also, Bank2 sensor2 always reads from 850mv to 1000 mv and never drops down. I know the rear o2s don't do anything but check the cats, but having so little oxygen behind the cat suggests unburnt fuel is definitely reacting in the cat. Bank1 sensor 2 reads much lower.
So here is what I think: The misfire is on the passenger side (bank 2). The cause is not a vacuum leak, because that would make the exhaust lean, not rich. The computer is correcting for extra oxygen detected at the front O2 by dumping in tons of fuel. Its possible that having such a bad mixture is causing the misfire. The extra oxygen is being detected because: a) i have an exhaust leak (or a bad AIR check valve), b) The O2 sensor or wiring is bad, or c) there is an actual misfire (not mixture induced) which intermittently lets unburnt air through one cylinder and into the exhaust. I swapped front and rear O2 sensors to try and check b and saw no difference, so I think its a or c. I tend to believe c is most likely.
So anyway, given all this information, can anyone give me a hint as to what I should try next. I'm broke, so I want to avoid swapping coils, plug wires, plugs, injectors, etc with no idea whats actually wrong. I know everyone will say get a tune-up, but at 60,000 miles I'd like to avoid spending the time/money. I really need a cheap way to see which cylinder(s) is/are misfiring and a way to check the ignition and fuel at each cylinder. I don't know where to go next so point me in the right direction.
Symptoms:
p0300 - Random/Multiple Misfires
Rough idle
Very rough under slight load at low rpms (shakes shifter all over when releasing clutch from stop)
Weak top end and rough low end, still pulls strong in the 3,000 - 4,000 RPM range
Smells rich, there's a fuel smell when cold and once the cats heat up it smells like a freakin skunk
Backfires out exhaust under load at low rpms.
SES light blinks under load and sometimes at idle, stays solid most of the time.
I have a cheap scantool that i was able to read some of the sensors with, but I was not able to read misfire counts on each cylinder. Both front O2s look to be reading fine, but the fuel trims look weird. Bank 1 long term bounces from 0 to 12%, which isn't great, but bank2 LTFT goes from 10 to 25%. Both short term trims bounce between +- 12%. Also, Bank2 sensor2 always reads from 850mv to 1000 mv and never drops down. I know the rear o2s don't do anything but check the cats, but having so little oxygen behind the cat suggests unburnt fuel is definitely reacting in the cat. Bank1 sensor 2 reads much lower.
So here is what I think: The misfire is on the passenger side (bank 2). The cause is not a vacuum leak, because that would make the exhaust lean, not rich. The computer is correcting for extra oxygen detected at the front O2 by dumping in tons of fuel. Its possible that having such a bad mixture is causing the misfire. The extra oxygen is being detected because: a) i have an exhaust leak (or a bad AIR check valve), b) The O2 sensor or wiring is bad, or c) there is an actual misfire (not mixture induced) which intermittently lets unburnt air through one cylinder and into the exhaust. I swapped front and rear O2 sensors to try and check b and saw no difference, so I think its a or c. I tend to believe c is most likely.
So anyway, given all this information, can anyone give me a hint as to what I should try next. I'm broke, so I want to avoid swapping coils, plug wires, plugs, injectors, etc with no idea whats actually wrong. I know everyone will say get a tune-up, but at 60,000 miles I'd like to avoid spending the time/money. I really need a cheap way to see which cylinder(s) is/are misfiring and a way to check the ignition and fuel at each cylinder. I don't know where to go next so point me in the right direction.
06-28-2012, 08:36 PM
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id put money on tune up it doesnt matter the mileage your at, your car is 13 years old stuff dryrots. but a good way is to pull the spark plugs and inspect not much else you can do without spending moneys the black ones are the cylinders missing
06-28-2012, 09:50 PM
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Well in pitch darkness I ran the car and put the hood up. If i position my head just right, I can see flashes of blue at cam speed. Its really hard to see exactly where it is happening, but I'm 90% sure cylinder 8 is arcing. Naturally it has to be cylinder 8, the hardest one to reach, but at least i have found the problem. Now I just need some good wires.
