John Speake

Unplugging the O2 sensor is useful as a fault finding pointer, not a way to pass emissions :-)

Fuelling is defaulted to mid range O2 loop, and is then critically dependant on MAF etc.

As the car runs much better with O2 disconnected, everything points to faulty O2 or LH ECU. I know you've changed them both. What's the history on the LH ?

Brett Jenkins

I didn't have the O2 unplugged to pass emissions, it was just still unplugged from my troubleshooting efforts.

LH is a rebuilt unit, just put in last week. O2 is less than a year old, but when I plugged it back in last night and reset the battery, the car ran like crap. I will be replacing the sensor shortly.

Would the O2 sensor affect drivability after the car is warmed up? My understanding was that it was only a factor when the car was cold, but after driving 20 miles this morning, my idle got choppy and the car just ran poorly. I unplugged the O2 and the car is running ok again.

John Speake

Yes, the drivability will be affected by O2 sensor when engine is warmed up. It's output is not used while the sensor is warming up. When car gets to about 60degC water temp, mixture control is closed loop using the O23 sensor.

So if can warms up running well, and then like crap when water temp gets to around 60degC. the problem could be O2 sensor/LH.

Brett Jenkins

Replaced the O2 sensor this weekend and I passed emissions today with flying colors.

John Speake

Excellent !

White Lightnin'

I forgot to update what was causing my "running on half the engine" problems...

one of the final stage modules was bad and was therefore only firing through the good one.

Didn't see that mentioned as one of the potential culprits though... interesting.