Gen III fuel trim

[offthepath]

On my 2003 I have got a few o2 sensor codes that pop up. The first one was about a year ago, cleared the code and never saw anything else.

On a recent trip the check engine light came on coming and going, both in full throttle long hill climbs. When the check engine light came on the traction control and stability control lights came on too. These do come on some what often, but this is the first time in conjunction with the check engine light.

When I got home I scanned the truck and it gave bank 1 o2 sensor not reading and a bank 1 mixture reading. Dumb on my part, but I cleared the codes and now can't remeber exactly what they were.... Ugh. I was going to replace the passenger o2 sensor sensor but then realized there are two sensors and becuase I don't have the exact code, I'm not sure which one I should replace. The CEL has not come on again and no codes.

I used the torque app to monitor the fuel trim. I can monitor each o2 sensor, voltage of each sensor and the short and long term fuel trim of each bank. The individual sensor reading numbers don't mean much to me and they seem to bounce around alot. One thing I noticed is that at idle the long term fuel trims for each bank is 12.5. During driving and acceleration bank one reads 5.5 while bank two is 4.7.

So my question is, what numbers should I be seeing and what's normal? For long term fuel trim, short term, and each individual o2 sensor? Im sure I have an o2 sensor issue based on the CEL, just not sure how to narrow it down.

Thanks

 

[EyeInTheSky]

From my understanding your trims should be +/- 5% most of the time. The 12.5 at idle is bad, and means your ECU is dumping more fuel into the system to maintain the stochiometric mix of 14.7-1 air to fuel.

Check the last couple pages of my build thread for my slaying of the 02 sensor gremlin (though I am getting a pesky P0171 now that seems to be due to both an exhaust leak AND a vacuum leak).

Try setting up Torque to watch 02 voltages and compare to the graphs in my build thread. Upstream should constantly cycle up and down, downstream should show less activity.

 

[offthepath]

Thanks. I set up torque like you did, seems. Much better to look at o2 readings. So the long term fuel trims should be 14.7 at idle?

Edit: reading more, LTFT should be closer to 0 correct?

 

[offthepath]

It looks like my o2 sensor readings are swinging up to 8-10% either way depending on throttle activity, with occasional peaks of 15%. I can't make out the numbers your sensors were ranging in the graphs you posted. Can you clarify? Also I'm not sure the LTFT of 12. 5 is bad. It goes to this with the key one, engine off. Maybe a default? During idle when LTFT is 12.5, STFT shows within 0-5%. Is anyone able to compare to their montero?

I noticed the voltage of bank 1 sensor 1seems a little more irratic than bank 2 but not sure if it's abnormal??

Interesting stuff watching the brains of an engine. But I still don't know what o2 sensor to replace! Lol. May just say **** it and change them all....