2001 F150 XL, 4.2L V6, RWD.

Here's the work I've done:
replaced coil pack, spark plugs, left O2 sensor and spark plug wires last year.
replaced DPFE and EGR valve last week.
replaced MAF last month.
Anyone have any idea what could possibly be going on? My inspection is (still) out and it wont pass until I get these codes cleared.

 

When you pulled the MAF out, the housing that it was screwed to, was it metal or plastic? I had the same issue and it had to do with the fact I was sent the parts out of a 4.6, which uses a metal housing for the MAF and the MAF had gone bad as well. A intake manifold gasket leak could cause those codes to be thrown or a leak after the MAF sensor to the TB. If your located near Austin, I know a guy who knows the 4.2 better than anyone else in the state and is someone I would trust more with a 2011 EB over the dealership.

 

It was a plastic housing.
and I'm in the DFW area.

 

I would check for Vaccum leaks or your O2 Sensors...maybe the right one is bad now???

 

but that wouldn't cause BOTH O2 sensors to read it as running lean would it?

 

well if it's telling you that your system is running lean, my first guess would be the vaccum leak. I would also suggest cleaning your MAF sensor but it's brand new.

 

PO171- Ford engine code for UH
PO174- Ford engine code for OH



I know this was no help

 

i will check for vacuum leaks

 

Go to Ford parts and ask about the TSB pertaining to the lower plenium chamber bolts and grommets. The new style is green, its a little pricey but does work. Save yourself the hassle and purchase all the parts from Ford not the gypo auto parts stuff. Believe me you only want to go at this repair once. Its a 45 minute repair that takes 3 1/2 hours.

 

i dont know if you have fixed yours yet but i had the same codes on my 5.4 and i diddnt think the truck was old enough for any of the sensors to go bad so i replaced the intake manifold gaskets and it worked like a charm .... a little bit of a pain because i hadnt done anything to a newer motor yet so it was interesting and learned alot