"Running lean in bank 2" code has been on in my '01 Reg. Cab F150 with the v6 5spd for probably six months atleast.

new O2 sensors before the cats. new fuel filter. new air filter. new fuel injectors and new MAF sensor.

Just got it out of the shop and two days later it came back to haunt me!

Any help would be GREATLY appreciated

 

Well, none of the things you did had much chance of fixing it...

Most likely, you have an intake vacuum leak. Gaskets and isolator bolts are the most common causes. Read some more of this sub-section for many threads containing SEARCH keywords "P0174" or "P0171".


Steve

 

This one was haunting me too. I finally found my solution yesterday. A vacuum leak. It was the rubber elbow on the passenger side intake runner, right near the firewall. It connected to intake air heater - hard to see and reach. A quick fix - if you have some old plug wires (distributor type), you can pull off one of the ends that snaps into the distributor. The resulting little elbow is the perfect fit.

I looked and looked for this leak - finally the little piece deteriorated enough that I could actually hear it leaking.. No more 0174s!!

 

If the 4.2 has the same manafold setup as the 3.8's do, they kick that light if there is a intake leak. There was some kinda a bolt update for the 3.8's. Maybe the 4.2's also

 

well have you checked the gasket on your throttle body at one time i added a TB Spacer & put the gasket in the wrong area & got the codes lean bank. check all connections from airfilter to TB as well!

Good Luck with vacuum leaks there a pain in the Rear!