2.3L ('02-'11) P0171 fuel trims

[tatermatt90]

Why would mine not be steady

 

[Dirtman]

The only reason the downstream (B1S2) sensor would fluctuate that much would be if the cat has failed but you would get a CEL. Are hou sure you're not looking at the UPSTREAM (B1S1) o2 sensor data?

 

[tatermatt90]

Yes b1s2 voltage at idle ranges from 0 to .7 v. Under acceleration it shows .8 v but will drop low. The b1s2 percentage is steady at 99.2

 

[Orca]

The b1s2 percentage is steady at 99.2

A few quick thoughts that may help a bit...

Your Zurich ZR13 scantool can graph up to 2 PIDs simultaneously. It would be very helpful if you could post a screenshot of your scantool while graphing the "O2S B1S1" and "O2S B1S2" voltages, either individually or (preferably) together.

Be aware that the steady 99.2% you're seeing for PID "STFT B1S2" means that that particular STFT value is meaningless -- 99.2% is how it says that that sensor is "not used in the calculation", which makes sense because "STFT BxS2" would be the PID associated with a downstream sensor.

In general, be reasonably careful with your interpretation and reporting of these PIDs. It can get quite confusing because the OBD2 standard (and, hence, your scantool) PIDs include STFT for a given bank in 3 places -- STFT for the bank, STFT for the upstream sensor on the bank (which always seems to match the former value, in my experience), and STFT for the downstream sensor on the bank (which is the meaningless PID I refer to above). Personally, I would focus only on the 1st value for STFT (i.e. what your scantool reports as "STFT B1", per the 1st image in your 1st post).

EDIT: Removed references to "Bank 2". I forgot that we're talking about a 2.3L engine here, which has only 1 bank, as your latest screenshot with the "O2SLoc" PID made clear!

 

[tatermatt90]

I'll do a graph next but here's a picture of how much the 02s b1s2 voltage varies

 

[tatermatt90]

So are the high fuel trims under load caused by dirty injectors? Truck sat for a year