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I'm no expert, but I have one experience where it did. I had multiple injector o-ring leaks that did show up in smoke tests on my (306k mile) Land Cruiser 80 series.
I agree with your logic. When I see the voltage pattern like Bank 1, Sensor 1, I know the sensor and fuel system controls are working.
Also get values for LTFT if you can, both sides. Although the values may have gotten biased by swapping sensors, my mechanic says LTFT between -5 and +5 is typical for a well sealed engine with good sensors. The high negative STFT for Bank 1 might be because the sensors got swapped, or fuel pressure is high. LTFT takes longer drive time to adjust to its final value.
Given the description above, I could have easily overheated the new sensor with the propane test and damaged them.
And I have smoke tested this engine several times and fixed all vacuum leaks. I can test again tonight, but I will be shocked if we have a vacuum leak.
Also, a vacuum leak seems inconsistent with how the same sensor had correct readings in bank B and also had good readings when swapped to bank A.
It feels more likely that I have one good upstream O2 sensor, currently installed in bank A, and a faulty sensor installed in bank B.
I need someone to check my logic, please.
Swap 1 to 2 To me, it looks like you have a vacuum leak on 2. The ECU commands rich on startup, and then a few seconds later it goes in to closed loop and fueling is based on the oxygen sensor. It looks to me like 2 is lean, it reads afr for a little while then when it goes to closed loop it goes lean and voltage goes to zero. Swap 1 to 2 and there will be three possibilities:
1. PS sensor is bad, DS sensor is good, and there is no vacuum leak. Sensor readings will swap left to right
2. PS sensor is bad, DS sensor is good, and you have a vac leak on PS. Both sides will go to zero.
3. Both sensors are good, PS has a vacuum leak, readings will not change.
Swap 1 to 2 To me, it looks like you have a vacuum leak on 2. The ECU commands rich on startup, and then a few seconds later it goes in to closed loop and fueling is based on the oxygen sensor. It looks to me like 2 is lean, it reads afr for a little while then when it goes to closed loop it goes lean and voltage goes to zero. Swap 1 to 2 and there will be three possibilities:
1. PS sensor is bad, DS sensor is good, and there is no vacuum leak. Sensor readings will swap left to right
2. PS sensor is bad, DS sensor is good, and you have a vac leak on PS. Both sides will go to zero.
3. Both sensors are good, PS has a vacuum leak, readings will not change.
@Extinct , this set of readings is all after swapping the working sensor from bank B to bank A. The sensor was also reading correctly in bank B previously. As described in your scenario 1.
I have new upstream sensors inbound - a Walker and a Bosch - that we will try in bank B. Unfortunately they don't arrive until next week. None of the local parts stores have one in stock.
Happy to help. Note also that LTFT at +25% is maximum addition of fuel and does indicate a large vacuum leak (air not measured by the MAF) if the O2s are working properly. Just remember, swapping the O2s could confuse the LTFT result, if one is bad.
@Extinct , this set of readings is all after swapping the working sensor from bank B to bank A. The sensor was also reading correctly in bank B previously. As described in your scenario 1.
I have new upstream sensors inbound - a Walker and a Bosch - that we will try in bank B. Unfortunately they don't arrive until next week. None of the local parts stores have one in stock.
If I assume Bank A = Bank1, then if I understand you had a working sensor in bank 2 and a dead one in bank 1, swapped them and now bank 1 does not work. If that is the case, then you have a bad sensor. Your chart does not look like a bad sensor, it looks like a big vacuum leak, assume those charts are from cold engine start. Starts out reading, then trends to zero like it is lean.
If I assume Bank A = Bank1, then if I understand you had a working sensor in bank 2 and a dead one in bank 1, swapped them and now bank 1 does not work.
Yes. What you describe is exactly correct.
Originally Posted by Extinct
If that is the case, then you have a bad sensor.
It is the case. Bad sensor.
Originally Posted by Extinct
Your chart does not look like a bad sensor, it looks like a big vacuum leak
The engine doesn't leak smoke anywhere when I run a smoke test and doesn't have any OBD vacuum codes thrown.
Originally Posted by Extinct
assume those charts are from cold engine start.
Yes. Stone cold engine.
Originally Posted by Extinct
Starts out reading, then trends to zero like it is lean.
But it never moves up from 0 (well 0.1v) once it drops, no matter how long it runs.
I'll replace the sensor with a new one next week. I ordered a Walker and a Bosch. Hopefully at least one of them works.
After I get a good sensor in there, I'll do some drive cycles while monitoring to see if I get different STFT and LTFT data.
