2008 Chevy Silverado 2500hd 6.0 P0174 bank 2 lean only

Ive had this issue for about a month now. I have smoke the intake and evap 3 times with no luck. I have no misfire codes and the truck runs fine. The long term fuel trim is pegged at 20 the short term is usually between 17-19 and only changes under full throttle. This is a fleet vehicle and the drivers original complaint was the check engine light and a rotten egg smell. My question is can a bad converter be causing the lean condition? Ive looked for exhaust leaks checked fuel pressure 64 with key on engine off and 47-55 with engine running and gone over the intake with a spray bottle of water but can find anythng. We also cleaned the maf sensor and check for cracks in the air tubes. Any ideas?

What does bank 2 sensor 1 oxygen sensor say when fully warmed up at idle

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It will fluctuate from around .6 to .89. I was told that the previous shop put 2 complete sets (upstream and downstream) in this truck before giving up on it.

A plugged catalyst can definitely cause a lean condition, depending on how badly the catalyst has failed. You end up with a lean condition because all the air that SHOULD have been flowing through one bank (the one with the plugged cat) ends up trying to flow through the other bank. If bank two is showing lean, then the problem is likely to be on bank one.

Are the short and long term trims showing above 15% on bank two while driving down the road? If so, then you can try doing a WOT run through first and second gears while watching the upstream O2 sensors. If you see bank one going rich, but bank two going lean, then we're on the right track. Here's an example of this test that I did on an '07 GMC with a plugged bank two converter.



Also note how the Load and MAF readings are very erratic at WOT. Another sign that the engine isn't breathing correctly.

Rotten egg smell is raw fuel being dumped into the exhaust. This will take out a cat. I would look, closely, into secondary ignition. Also, a non-firing (no flame) cylinder will cause a lean condition. The un-burned oxygen causes and O2 sensor to go lean. The un-burned fuel produces the rotten egg smell.

Bank 2, Sensor 1 fluctuates from .6 to .89? Are you sure that is Sensor 1 (upstream). That would indicate a RICH condition on an UPSTREAM sensor. It sounds about right for a DOWNSTREAM (sensor 2), though.

Thats what has me confused. The downstream sensor doesnt move hardly at all on bank 2. Now I did swap b2s1 with b1s1 and it did fluctuate but the one i put back in bank 2 did the same thing as the first.

That is what happens. When you do a Wot bank 2 starts to come down to normal and bank 1 does richen up . But the minute you just try to cruise down the road the fuel trim goes back to 17-19 on short term. Longterm is 20.