So I made a thread a few days back concerning lean / irregular AFRs during idle. I thought it was the IAC but it turned out it wasn't.

Yesterday, I went ahead to check what my Fuel Trim values were at. Lo' and behold, fuel trims were at 0 during idle, oxygen sensor 1 and 2 were jumping from 0.0V to 0.9V and anything in between, but mostly around the 0.0xyzV range.

This was weird as I had just purchased a brand new O2 sensor. So I went ahead and replaced it with my friend's O2 sensor that was working. Same thing.

I took the car out, being a bit optimistic that MAYBE it was just during idle that it was acting weirdly, but deep down I knew I was just lying to myself, and indeed, AFRs at low speed cruising were around the 11-12 mark, and no fuel trim values appeared.

Now I'm stumped and I don't know what may cause this and how it can be resolved.

If anyone knows of a way to diagnose the culprit of this issue, please, do not keep such worthy knowledge to yourself. Sharing is caring.

I took out the negative terminal going to the battery for a minute or so, but Fuel Trims still do not appear. Waited for 10 minutes, still no luck. Changed O2 sensor, again, nothing.

Help.

 

That's what it's supposed to do.

It means it's in closed loop.

 

Have any of the settings been messed with, in relation to when it goes between open/closed?

 

If oxygen sensor #1 is reading anything, it's means you're in closed loop. Look for you Short Term Fuel Trim, or O2 feedback trim. See what that says.

 

Nope, nothing has been touched.

I don't know about "anything".. Searching around in the numerous unresolved threads in the forum, what I understood was that the sensor should be giving out values between 0.2V and 0.9V. If my memory does not deceive me, I think Aaron from English Racing replied to a thread, whose creator was running in to a similar conundrum as I am, stating the above. This is why I am 98% convinced my car is not going into closed loop.

As for STFT and O2 feedback, both 0 as well. The O2 feedback might randomly throw out a negative value from time to time when I give it some throttle, but other than that, zilch, nada, rein, miski, niks, nicht, etc etc...

 

If it's stock unmolested , that's how it should be........It's in closed loop and tuned right.



The problems arise with the first mod done wrong........fitting a fuel pump that's too big.
Fuel trims change due to incorrect pressure in turn caused by outflowing the FPR.



So what you've done here is to start a thread thinking it's broken when it's not because everyone else's modded cars are broken only they think they're not.