Post-cat Long-term fuel trim at 99%...wtf?

[GRWeldon]

I thought our cars used the post-cat O2 sensors to adjust fuel trim. Did I imagine reading that somewhere?

The exhaust system on this car has been mangled. For some reason somebody cut each pipe after the cats an then re-welded them back together (pretty horrible job). It fits the manifolds without hitting anything else but its pretty bent out of shape. As far as i can tell visually looking in to the cats, they are not clogged.

I'm running some Berrymans injector cleaner in the fuel but the injectors were clean of carbon when I put them in. I HAVE new O2 sensors but I really hate to throw the parts cannon at it until I can check the simple things. The short-term fuel trims are fine at less than 5%. I'm assuming that means the pre-cat O2s are working correctly?

I also have a new MAF sensor as I'm sure the one in it is original, again, parts cannon and all. I bought all these parts years ago when they were way cheaper and I hate to use them if I don't know the existing ones are bad.

Clean air filter, new fuel filter. The tank on this car was the worst I have ever seen. I'm not using the same injectors that came out of the car. Pretty sure I have taken care of all the vacuum leaks.

I suppose I'll clean the MAF first but I'm not hopeful. Any other suggestions before I change the O2s?

 

[Jim3inVirginia]

The high trim number just means the scan tool is not getting a reading so it is defaulting to the max value. Probably the PCM is not designed to read post-cat fuel trims. Pre-cat sensors sound fine to me, too. And you're right, try a MAF sensor cleaning first. With MAF sensor cleaner. I'd be optimistic that it will be just as good as a new sensor. Too bad I am so far away, I've got a stock original exhaust system I'd love to see get used.

 

[GRWeldon]

If I understand you screen name, you are in Virginia? I would be willing to come and get it. Hopefully you are in south Virginia?