Thread: Fuel Trim Diagnosis

You need to get a better diag tool onto it and check the injector trim values. You’ll probably find them at max limit, leading to injector replacement.

On a D2 V8----
The O2 value should be constantly changing .1 up to .9v.....

afaik thats how all O2 sensors work

The most common problem with the Ford V6 is timing chain stretch.

Have a google of it.
Regards PhilipA

Originally Posted by Pedro_The_Swift

On a D2 V8----
The O2 value should be constantly changing .1 up to .9v.....

afaik thats how all O2 sensors work

Narrow band o2 sensors work that way as they are effectively a switch - lean or rich and so to get the perfect economy, when in cruise they would adjust the mix to sit between the two flicking back and forward.
Wide band o2 sensors are able to read values throughout the operating range and constantly, thus they can be used for tuning and far better fuel economy management. These days cars tend to use wide band as emissions are key.

When I used to tune cars in the 90’s I paid a lot for a wide band sensor out of the US to stop my engines going bang.

and the 4L uses wideband?
and "should" read 50?
if its reading 60 shouldnt the STFT's all be negative?
and how do you tell if a wideband's gone bad?

So I disconnected the MAF and ran her for about 20 seconds.. these were the results:

STFT1 16.41
LTFT1 -17.97
STFT2 17.97
LTFT2 -15.63

Does this confirm a bad MAF?

Originally Posted by ellzeez

So I disconnected the MAF and ran her for about 20 seconds.. these were the results:

STFT1 16.41
LTFT1 -17.97
STFT2 17.97
LTFT2 -15.63

Does this confirm a bad MAF?

You can’t just disconnect the MAF and expect it to run well. No it doesn’t

Haha yeah might be being a bit naive and clutching at straws, but trying to eliminate some stuff. Just going with something I saw on another forum. Didn’t change the way it ran apart from a bunch of gearbox warnings