CEL Code Troubleshooting Random Misfire and Lean Condition
06-26-2013, 10:47 PM
#1
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CEL Code Troubleshooting Random Misfire and Lean Condition
Just bought a MY02 S2K last week, 78k miles. Next day I started getting CEL for P0170, P0171, and later P0300, P0301, P0303, P1399.
Using this forum I tried the following: Cleaned MAP Sensor. Cleaned throttle body. Cleaned IAC valve. Checked for vacuum leaks using propane- no leaks found. Reset ECU for idle mapping. After that, the car ran noticeably smoother.
Codes showed up again. Checked spark plugs. Plugs looked good, but gaps were OOT- the worst was about .065. Replaced spark plugs with NGK Laser Irridium plugs. Car ran even better. Cleared codes.
Codes showed up again. Swapped coil packs, did cylinder compression test. Compression was awesome (didn't really think this was a problem, but wanted a baseline for compression anyway- now I know for future reference.
Codes showed up again, random misfiring. At this point I am thinking the random misfire suggests it's not isolated to something like an injector, or coil pack- seems to happen to everything. I had been suspecting the front O2 sensor, even though there's no O2 sensor specific CEL. O2 sensor came today so I swapped it. See my DIY post for that if you have questions. The car runs really smoothly now. The idle was noticeably better, response is better when I let off the throttle in neutral, and the car seems to shift better at cruising speeds. I never seems to have trouble at WOT or engine warm-up, BTW.
I also don't suspect it is a fuel pump, only because that would be very uncommon for a car with 79K miles and only 11 years old, IMO. Time will tell if the O2 sensor has resolved the issue. I hope so. I will keep this updated. If the problem persists, I have heard there is a method for checking injectors using an ohm meter and checking for resistance differences from injector to injector. I might also try swapping injectors to trace a moving problem, but so far the misfire was random. I just don't think all injectors are going bad intermittently, or the coil packs.
May the VTec be with you.
**UPDATE** The 02 sensor seemingly was the answer. No trouble codes since.
Using this forum I tried the following: Cleaned MAP Sensor. Cleaned throttle body. Cleaned IAC valve. Checked for vacuum leaks using propane- no leaks found. Reset ECU for idle mapping. After that, the car ran noticeably smoother.
Codes showed up again. Checked spark plugs. Plugs looked good, but gaps were OOT- the worst was about .065. Replaced spark plugs with NGK Laser Irridium plugs. Car ran even better. Cleared codes.
Codes showed up again. Swapped coil packs, did cylinder compression test. Compression was awesome (didn't really think this was a problem, but wanted a baseline for compression anyway- now I know for future reference.
Codes showed up again, random misfiring. At this point I am thinking the random misfire suggests it's not isolated to something like an injector, or coil pack- seems to happen to everything. I had been suspecting the front O2 sensor, even though there's no O2 sensor specific CEL. O2 sensor came today so I swapped it. See my DIY post for that if you have questions. The car runs really smoothly now. The idle was noticeably better, response is better when I let off the throttle in neutral, and the car seems to shift better at cruising speeds. I never seems to have trouble at WOT or engine warm-up, BTW.
I also don't suspect it is a fuel pump, only because that would be very uncommon for a car with 79K miles and only 11 years old, IMO. Time will tell if the O2 sensor has resolved the issue. I hope so. I will keep this updated. If the problem persists, I have heard there is a method for checking injectors using an ohm meter and checking for resistance differences from injector to injector. I might also try swapping injectors to trace a moving problem, but so far the misfire was random. I just don't think all injectors are going bad intermittently, or the coil packs.
May the VTec be with you.
**UPDATE** The 02 sensor seemingly was the answer. No trouble codes since.
06-27-2013, 05:06 AM
#3
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Your first two codes are O2 codes. It's always best to resolve them in order.
If an O2 code goes too long unchecked it'll start to cause misfires, which in your case it did, and eventually could result in catalyst damage. I guarantee replacing the O2's fixed your problem.
I've had a few engine problems on my S and every time the motor isn't happy it affects shifting smoothness tremendously. Just my observation.
If an O2 code goes too long unchecked it'll start to cause misfires, which in your case it did, and eventually could result in catalyst damage. I guarantee replacing the O2's fixed your problem.
I've had a few engine problems on my S and every time the motor isn't happy it affects shifting smoothness tremendously. Just my observation.
06-27-2013, 07:08 PM
#6
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Thanks for the feedback everyone. Drove the car to work, to the DMV, the gym, and home today. No CEL so far. Drives great. Love this car. I think the O2 sensor was the culprit- but I am glad I did everything else anyway. Runs smooth and I got to know my car a little. Not bad for my 1 week anniversary 
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