Fuel trims / O2 Q's

[FunnyGas]

so i got my logger working.
i am using MMcd logger on my palm.
one thing have noticed.
O2-F and all 3 fuel trims are stuck at a constant number.
O2-F has never moved from 2.51v
FTRL, FTRM, FTRH have never come off of 100%
this is after 3 days and about 200km of logging
any ideas?

 

[16gpoweredgsx]

It's probably a bad o2 sensor. That is what happened to mine. Does your o2 cycle at idle or is it stuck?

 

[FunnyGas]

O2-R is, O2-F is stuck at 2.51v all the time, idle, wot, cruising... all the time

 

[FunnyGas]

also, i just put a brand new O2 sensor in the O2 housing when i swapped in the evo3-16g...,

 

[MyEclipse5]

Your a 1G, so you don't have 2 O2's. The one that is bouncing at idle is the O2 that you have, the other shouldn't read anything because if im not mistaken its not hooked up to your O2 sensor thats in your housing. Mine is stuck at the same number, don't pay attention to it.

Correct me if I'm wrong. Cause If i'm wrong, I have the same problem, .

 

[spyderturbo007]

MMcd is weird. O2-F really isn't the Front O2 sensor. You want to look at O2-R, which for some stupid reason is actually the front O2 sensor.

 

[bling5tatus]

yeah, my short term fuel trim is stuck at 92%, I adjusted the afc a bit and waited for probably 3 or 4 minutes, it never changed from 92. I wonder if my o2 sensor is bad. It seems to read properly, but it also doesn't do the bouncing thing that it should. It has .9 volts at idle which is probably about right, either a bit rich or a bit lean.... anyway, is there any reason it wouldn't be moving my fuel trim? Or does it take like 10 minutes before the fuel trim moves?

 

[Calan]

MyEclipse5 is correct... The O2-R reading in mmcd is what you should see changing, not the O2-F.

With that said, don't worry about either one of them too much . Monitor the O2 trim (FTO2).... It responds to the O2-R signal, and is displayed as a percentage the same way as the Low, Mid, and High trims so it's easier to read. It's a real-time fuel correction based on the O2-R value, and is used to help set the other trims.

The Low, Mid, and High trims are the ECU's way of predicting what it's going to have to do to maintain a proper AFR in closed loop. They will only change when the ECU sees a consistent engine state for a certain amount of time, and when they actually need to. For example, changing your idle air/fuel will have no affect while you are cruising down the road at 70mph. You would have to be at steady idle for a while so the ECU can monitor things and determine if it needs to adjust the Low trim. Likewise, the High trim requires a constant load at cruising speed for a while before the ECU will make any adjustments.

In my experience... changing RPM's (even a little), more/less airflow, going up a hill, etc. can all prevent the ECU from adjusting the trims. It wants a very specific and steady engine state before it will change them.

 

[bling5tatus]

i see, makes sense, my car has a slight idle surge.... so that makes sense that it's not changing my stft.