2002 5.4l 4x4 130,000 miles. So i've been throwing a P0171 code (bank 1 too lean). This is the only side thats lean. Ive been doing some troubleshooting and still can't find the problem.

First thought was pcv valve. Got a new tube and valve replacement from ford dealer, nothing changed.
Second thought was maybe a bad o2 sensor. Switched my drivers/passenger o2 sensors, same code.
Third thought was a possible vacuum leak somewhere else on that side of engine. I sprayed that side down with carb cleaner at all vacuum spots and couldnt find anything. This is an ok test but not the best.
I also cleaned the MAF sensor...

Since I know its not pcv or the o2 sensors, I'm almost positive its a vacuum leak on either the exhaust manifold or intake manifold. Im going to try to get a smoke test done tomorrow to see if they can find anything. Any other ideas guys? I'm pretty stumped...

 

Did you retorque you manifold down after 5 heat cycles after you did the headgaskets?

 

No, I didnt know I was suppose to. You happen to know what the torque spec is? Or where can I find it? Remember this is only one bank. If manifold was loose wouldnt that throw codes for both banks?

 

The first thing I would check would be the exhaust manifold especially since ours have so many cracking issues. A smoke test would be perfect to find a small leak. If a manifold was leaking it would only set a code for that side.

 

Just put headers on a few months back. Gaskets should be fine there. Sprayed carb cleaner around it and still nothing. Hopefully going to get a smoke test done today.