o2 voltage drop

[demografik]

so my car's running rather rich, on stock fuel and ecu. read: james bond smokescreen and black rear bumper.

troubleshooting starts at the o2 sensor. my logger says it's normal at idle, fluctuating a little bit but mostly around 500 mV. however, every once in a while for one refresh it will read down to 20-40ish mV. is this normal? i'm using obdgauge.

 

[bluetlr2001]

Your o2 volts will fluctuate but just keep an eye on your fuel trims to know if its feeding to much fuel or not. You want your trims to be around 0 (+ or -5). But it still being stock it is goign to run rich. I believe the ecu is set to keep the AFR around 9:1 ratio. Most people after tuning try to go for 10.5:1 ratio. I would do a boost leak test on it and see if you have any boost leaks.

 

[demografik]

i understand that fluctuation is normal. i'm asking if the major drop every once in a while is normal. it fluctuates between 200-800mV but every once in a while drops down to 20-40mV.

i also understand that from the factory it will run a bit rich but it shouldn't be so rich i leave clouds of black smoke. i don't have any boost leaks.

 

[spyderturbo007]

Unless you're under decel, it shouldn't be dropping that low. AFR target during closed loop is 14.7:1 and at WOT it varies, but the highest airflow map AFR target is 9.5:1.

Are you getting this black smoke during idle / cruise, or during WOT?

 

[demografik]

WOT. the readings i'm experiencing are at idle.

 

[spyderturbo007]

Sounds like your O2 sensor might be on it's way out, but without looking at your fuel trims, I can't tell for sure. Typically, O2 sensors just die and report a voltage of 0.00v to the ECU all the time, but I have seen them get sluggish. It will still cycle, but not as quickly as it should. Either way, a dead O2 sensor won't have any effect on WOT operation.

You said you don't have any boost leaks, but are you sure? What did you pressurize the system to and how long did it hold that pressure?

Have you checked out all the other parameters at idle, such as coolant temp, IAT, STFT, LTFT, etc? Posting a log at idle and WOT would make this much easier. At idle, log STFT, LTFT, airflow, rpm, coolant temp and IAT.

Then, for the WOT log, verify that the TPS reads close to 100% at WOT, then make a 3rd gear pull from 2.5k to redline logging only RPM, timing, airflow and front O2.