I have an 02 f-150, 4.2 V6 with 108,000 miles on it, and no mod's and am finally having a problem with it. I'm still getting codes171,174, lean burn banks 1 and 2 from my truck. Now it has started throwing codes 1131, 1151 which I'm told is either failure to switch or eccess O2 at the upstream sensers.
Ive changed O2 sensers, the fuel and air filters, tried Torkums suggestion about spraying carb cleaner in the oil fill, and poked and played with every thing I can think of with no results. Anybody got any ideas before I break down and take the truck back to ford to find out what my problem is. ???

 

When you tried the forced vacuum leak and spraying carb cleaner did the 02s move? You did'nt say about checking your fuel pressure.

 

P0171 and 174 are because the computer is at its limit trying to richen up the AF ratio enough to get the O2 to switch. This is either caused by a vacuum leak in the centeral part of the maniflod, (because it effected both banks) or a dirty or bad MAF, a dirty MAF is very common. your other codes, P1131 and 1151 are pretty much the same but a manufactor specific code, (P1), the computer cannot add enough fuel to get the o2 to switch to rich. Remember like torkum said if fuel pressure is low it can also cause this. Hope I helped alittle!

 

Proably the MAF -- google how to clean ford MAF. Remove it from the truck clean it good.

 

I have had my truck since December, after one month I got the 1151 code. I changed out the Upstream O2 sensor that was indicated. Then I started getting 1131 and 1151. From there we changed plugs, 2 fuel filters, 2 air filters, a new MAF. After all of this, I was still getting 1131 and 1151, so I changed the Idle Air Control. After this I started getting 0174. Finally broke down and went to ford and picked up the upper intake manifold port gaskets, new isolator bolts, and the gaskets between the center section of the upper intake and plenum. Truck seems to be running better, but now I am having problems where if I start going downhill it seems like it is searching for a gear and keeps shifting in and out of overdrive, but 1131 and 1151 is gone, and most of the fuel mileage is back. There is a tech bulletin about it. It cost about $120 for the parts. Good luck

 

I am having the same codes with my F-150 2001 4.2. The plastic intake where it meets the aluminum lower intake is leaking. The gasket set is about 38 $ at advance auto but you need to replacce the 8 bolts that hold the intake down. They are rubber coated & help seal the intake & they are a dealer only item & are about 60$ from Ford. This shoud clear up your codes or if you are lucky it may be a leaking vaccum line. Good luck!

 

I read somewhere that over oiling a K&N etc. high performance air filter could dirty up your MAF. I had the P0174 code the other day and replaced my driver side O2 sensor and erased the code. Check engine light hasnt come back on yet.

Now my check engine lights back on again.