Very Low o2 voltage - bad sensor?

[spoolin_upTSi]

Recently i have been fouling out spark plugs in a matter of 2 days so I got a wideband and found out I am running very rich, especially at idle (~11:1). So i hooked up a logger to the car and got codes for both o2 sensors, and p0505 which is idle control. During a third gear pull I logged I can see that the front o2 sensor is maxing out at .08v. This seems VERY low, is my sensor done? I just ordered a new one because I felt completely confident that this is the problem.

 

[Gstclipse69]

Yea the sensor is done for. I just changed mine out because I was getting .02v at wot. Put in the new sensor and see what happens. Keep in mind the the stft will change immediately with the new sensor but the car has to be up to normal operating temp and the ait < 84 and some barometric value as well for the ecu to change the ltft. Do you have a safc or another tuning device? Seems odd your afr is that rich at idle.

 

[kenamond]

When cruising or at idle, the front O2v should oscillate around 0.5v. If it's staying low, the sensor might be bad, or you might have a vaccuum leak. Also, if you have vaccuum leaks, I get the impression that the car will idle high, and the ISC might not be able to compensate (goes all the way to one end of the spectrum) and throws P0505. But I'd search around about P0505 and see if anyone has had similar problems and how they fixed it. Go ahead and replace the front O2 sensor, check for vaccuum and boost leaks, and see if things improve. If you have consistent lean O2v, your LTFTs are probably way high...have you checked your LTFT?

If your VC breather isn't run to the intake pipe, that'll be a vaccuum leak. Think about those sorts of things.

 

[spoolin_upTSi]

have you checked your LTFT?

Yeah I logged the LTFTs. Here is a portion of the log.

RPM LTFT
3250 12%
4285 12%
4542 12%
4761 0%
5507 0%
6441 0%
3441 12%

So while i was WOT the 12% dropped to 0 at 4761 and then went back up to 12% after I shifted to a higher gear near redline.

Here are my significant mods if it helps anything:
98 gst spyder
evo 16g at 18psi
FMIC
650 injectors
255 pump and afpr
safc2

 

[kenamond]

Yeah I logged the LTFTs. Here is a portion of the log.

RPM LTFT
3250 12%
4285 12%
4542 12%
4761 0%
5507 0%
6441 0%
3441 12%

So while i was WOT the 12% dropped to 0 at 4761 and then went back up to 12% after I shifted to a higher gear near redline.

I don't know what's wrong, but something's wrong . I vaguely recall that the LTFT is supposed to be within +/-5%.

 

[always_broken]

LTFT means low throttle fuel trim right? Like the safc2 settings you can adjust the fuel curve on Low and High. So I'm guessing this is it?

Should I be logging these both? Currently I'm logging RPM/Front O2/Timing/Coolant temp/TPS/Airflow

I'm about to take the coolant temp off because I'm getting a regular 200 temp, but that should change soon because I've been doing a lot of researching on cooling methods. Anyway, please let me know.

 

[p1s70np0w3r]

Did you replace all off the o2 sensors there is more than 1 on a 2g.

 

[steve]

LTFT means low throttle fuel trim right?

Long Term Fuel Trim. There is also a STFT Short Term Fuel Trim that is the real time feedback from the front O2 sensor and over time it will be averaged into the LTFT.

The trims are only updated while the ECU is in closed loop.

Any of these will cause the ECU to drop out of closed loop. (copied from the DSMLink Wiki)

* Throttle position too high (varies by RPM)
* Airflow too low (units are tricky, but it's very low)
* Coolant temp < 51F
* Coolant temp > 228F
* The O2 sensor did not switch around 0.5v for over 128 seconds while running in closed loop mode. In that case, the ECU locks itself in open loop mode.

All of the following have to be true for a full 5 seconds. If any single one is not true even for a millisecond, the timer starts over and trends in STFT will not be moved into LTFT.

2G Learn mode (all must be true)

* Coolant temp >= 180F
* Intake air temp < 133F
* Baro >= 22.9 inHg
* Baro <= 31.6 inHg

 

[always_broken]

Long Term Fuel Trim. There is also a STFT Short Term Fuel Trim that is the real time feedback from the front O2 sensor and over time it will be averaged into the LTFT.

The trims are only updated while the ECU is in closed loop.

Any of these will cause the ECU to drop out of closed loop. (copied from the DSMLink Wiki)

* Throttle position too high (varies by RPM)
* Airflow too low (units are tricky, but it's very low)
* Coolant temp < 51F
* Coolant temp > 228F
* The O2 sensor did not switch around 0.5v for over 128 seconds while running in closed loop mode. In that case, the ECU locks itself in open loop mode.

All of the following have to be true for a full 5 seconds. If any single one is not true even for a millisecond, the timer starts over and trends in STFT will not be moved into LTFT.

2G Learn mode (all must be true)

* Coolant temp >= 180F
* Intake air temp < 133F
* Baro >= 22.9 inHg
* Baro <= 31.6 inHg

Thanks Steve.