My fuel trims have been having difficulty staying close to 0 for a while now. In the past few days my idle LT's have been holding steady at B1: 5.8%, B2: 19.5%.

What's got me stumped is I've leak tested everything with vacuum, smoke tested, pulled off vacuum lines and plugged. I found a leak at the vacuum booster hose on the intake and fixed (dropped B1 from 10% and B2 from 25%). Nothing else has really changed the LTs any.

However, when I pulled the vacuum line to the pressure regulator and capped the nipple on the intake, my B1 went to 1% and my B2 dropped to 13%. There is, as far as I can tell, no vacuum leak present at the regulator or gas leaking. Fuel pressure @ idle is 51psi spiking to 56psi with regulator unhooked.

Is there something obvious I am missing like O2S aging that would cause the LTs to skew? Since the truck is cat-less I can definitely smell the fuel/air mixture and I'm thinking the fuel smells stronger than usual. No rough running problems other than occasional start, stumble, fumble and stall.

 

The fuel trims between banks 1 and 2 consistently average that large of a variation between the two? Have you checked thoroughly for any exhaust leaks anywhere around or before the O2 sensors? I've seen even a pinhole size hole at an exhaust bung cause some moderately lean fuel trims.

 

It's been pretty consistently off balance and the difference has been getting bigger over time and not smaller. I may have an exhaust gasket problem since the B2 gasket has been off a few times (B1 is new). I'll stick a new gasket on it and see what happens.

Fixing to have turbo manifolds on it anyhow so if there's a leak I'll probably fix it in the process.

 

Swap the sensors side to side see if the gap is the same, if it is not the you have a bad o2 sensor. How many miles are on them.

Btw, my o2 sensors have always been within 3-4% of each other.

 

I've got about 30k on these. They've been out a couple of times.