o2 sensor issue

[englundjd]

I am having an issue with my passenger o2 sensor, Its a brand new Delco sensor (please note the old sensor had the same issue). Its not fluctuating like normal. Its just hanging out around 850mv. I just got done messing with the wires, I visually inspected the factory harness and I checked continuity of all 4 wires in my extension. Everything seems good... The one thing I found while inspecting was that the plug on the factory harness was super dirty so i cleaned it up and shoved everything back in there.

I am thinking that maybe i'll switch the o2 sensors around and see if the issue moves to the drivers side... maybe i'll get lucky and find my issue... Any other ideas?

[Injuneer]

What does the voltage read if you unplug the sensor? Should be ~450mV. If it's anything else, it's a wiring problem... Possibly voltage leaking from the 12V heater circuit.

[BALLSS]

do you have a exhaust leak pre 02?

[englundjd]

do you have a exhaust leak pre 02?

No exhaust leaks that i can hear, ive tightened up all my header bolts, I just swapped o2 sensors side to side and problem stayed on passenger side... we ohmed out and checked the injectors for leaks on the passenger side. @Injuneer what wire needs 450mv on it?

[Injuneer]

How did you read the ~850mV? Assume you used a scanner. With the sensor showing ~850mV, unplug the sensor harness connector. That should cause the PCM to show ~450mV on the scanner. The PCM provides 450mV reference between the signal wire and the ground. The thimble in the sensor adds to or subtracts from that value depending on the difference in O2 content between the exhaust gas on the outside of the thimble, and ambient air on the inside of the thimble. Don't try to measure it, read it on the scanner.

Do you have any codes? If the passenger O2 stays above 700mV for 50 seconds, and the throttle angle is greater than 4%, it should set DTC 65. Was the PCM in closed loop when you observed the 850mV reading? It won't start to cycle until it's in closed loop. 850mV would NOT be unusual for enriched cold start.

Exhaust leaks before the O2 sensor would make the sensor read "lean" (below 450mV). And, the PCM would use the STFT's first, and then the LTFT's to correct (even when it doesn't need more fuel), resulting in the sensor continuing to cycle back and forth, with an average value of 450mV..

[englundjd]

How did you read the ~850mV? Assume you used a scanner. With the sensor showing ~850mV, unplug the sensor harness connector. That should cause the PCM to show ~450mV on the scanner. The PCM provides 450mV reference between the signal wire and the ground. The thimble in the sensor adds to or subtracts from that value depending on the difference in O2 content between the exhaust gas on the outside of the thimble, and ambient air on the inside of the thimble. Don't try to measure it, read it on the scanner.

Do you have any codes? If the passenger O2 stays above 700mV for 50 seconds, and the throttle angle is greater than 4%, it should set DTC 65. Was the PCM in closed loop when you observed the 850mV reading? It won't start to cycle until it's in closed loop. 850mV would be unusual for enriched cold start.

Exhaust leaks before the O2 sensor would make the sensor read "lean" (below 450mV). And, the PCM would use the STFT's first, and then the LTFT's to correct (even when it doesn't need more fuel), resulting in the sensor continuing to cycle back and forth, with an average value of 450mV..

Yes i was scanning with Tuner Pro RT. I have no codes present at the moment. I have an injector fault but I went ahead and went though all the injectors and checked the harness voltage and ohmed out the rest of the injectors, they are all playing nice, no leaks no nothing. I'm not sure why it says i have an injector fault lol

Also this condition is in closed loop, its starts enriching up on the sensor before the car even goes into closed loop...

[Injuneer]

See edit to above post. 850mV would NOT be unusual for enriched cold start - without a functioning AIR pump.

If you verified 12V on the pink wire at each injector connector, and 12-16 ohms resistance across each injector, did you also verify the PCM is providing a ground to fire the injector, and the ground was reaching the injector by using a noid light?

[englundjd]

See edit to above post. 850mV would NOT be unusual for enriched cold start - without a functioning AIR pump.

If you verified 12V on the pink wire at each injector connector, and 12-16 ohms resistance across each injector, did you also verify the PCM is providing a ground to fire the injector, and the ground was reaching the injector by using a noid light?

I dont think the issue stems from the injectors not opening because its rich not lean... Injectors ohmed out at 12.5v all across the board and yes we are getting a strong voltage reading from the harness... iirc every one of them was around 13.5v. They are stock injectors though, what i'm wondering is if there just shot and not flowing even. I have a set of 30# injectors i could put in.

[Injuneer]

You get the injector fault code if a single injector circuit is faulty. One injector not firing would dump a lot of air into the exhaust. The O2 sensor would then read lean, and the PCM would start dumping a lot of extra fuel, causing the healthy 3 cylinders on that bank to run rich.

But none of this is going to cause the O2 sensor to sit steady at ~850mV in closed loop.

[englundjd]

You get the injector fault code if a single injector circuit is faulty. One injector not firing would dump a lot of air into the exhaust. The O2 sensor would then read lean, and the PCM would start dumping a lot of extra fuel, causing the healthy 3 cylinders on that bank to run rich.

But none of this is going to cause the O2 sensor to sit steady at ~850mV in closed loop.

I'll check the voltages and ohm the injectors again and see if I missed anything. What pins on the pcm plugs go to the o2 sensor? I could check continuity there to...