1995 850 GLT O2 Sensor closed loop fault

[moacyr]

It's because ecu is programmed to totally ignore data from o2 sensors on hard accelerating(full throttle) and to use default values.The reason is that car always have it's maximum power when it needed and there is no risk that ecu will cut off fuel because o2 sensor reads too rich at the moment.

Btw...did you reset codes after o2 sensor replacement?'95 have built in diagnostic tool under the hood.

No, I have not. Forgot to do so. Where is this built in diagnostic tool located?

[JDS60R]

Your maxed out on fuel trim . The car is adding 25% more gas than needed (it thinks its hyper lean). You need to find where the extra (unmetered) air or faulty sensor data is coming from . The oxy as shown is working on a normal pattern but you are running full rich 25%+ltft as it thinks its full lean. You have to figure out why it thinks its full lean and why the oxy sensor isn't reflecting it.

Time to look at the sensors that control A/F ratio - O2 (both) , MAF, ECT (coolant)
as well as major air leaks or dirty injectors or low fuel pressure .

That oxy sensor is a regular pattern but should be pegged at .1 volt if the engine was really running that lean.

Lets map out both oxys, the maf, coolant temp sensor and trims. So you can see the whole picture.
Raise rpm to see what happens . If its a small air leak the trim should get better with higher 3K rpm.

[JDS60R]

If it ran correct before the o2 change - get rid of that O2 sensor. Make sure to change both with direct fit Bosch ( if OE was bosch)

That open loop period could also be an open circuit as an O2 (zirconia) sensor makes its own voltage.

[misha]

No, I have not. Forgot to do so. Where is this built in diagnostic tool located?

http://volvospeed.com/volvo_repairs_how ... es_a2.html

[moacyr]

Recorded the readings

Includes:
Sensor voltage output 0V
ECT average 90°C
Speed average 65mph
Loop remained Open Fault at all times

[misha]

I would say that your o2 sensor is dead.It is o2 sensor or the wiring.It doesn't produce voltage at all and there are no readings from it.
According to all this data,the car must be running super rich(black smoke from the exhaust and abnormal fuel consumption.

[JDS60R]

Minimal change at higher rpm. Look for sensor issues instead of mechanical.

ECT of 90c (194f) is ok but a touch low - not worried about it.

Where are both oxy readings ???

[JDS60R]

Show me your 4 graph like this

oxy 1 oxy 2

ltft stft