I got a 2003 f-150 5.4 Triton with 205,000 miles. runs strong but has 2 lean codes- po171-po174. Has new o2 and maf sensor and pcv works. I cant see or hear any vacuum leaks. Does anyone else have this problem or have an idea whats wrong.

 

Check vehemently for vacuum leaks/hoses out of place.

if you have a code reader, you can use it to read the fuel trims and see if you have an obvious vacuum leak that way too.

 

could it be the fuel injectors

 

Don't scare anyone though - https://www.dictionary.com/browse/vehemently

There's another guy with a similar problem. https://www.f150forum.com/f6/2003-f1...2/#post6485407

 

When you say "pcv works" do you mean you checked the pcv operation or you replaced 'the works'? I had P0171 and P0174 codes as well and remedied the problem by replacing the upstream 02 sensors and the infamous rubber elbow (part of the pcv system) under the throttle body. You say your 02 sensor has been replaced (I take it you mean more than 1 - on my 1999 4.2l there are 4) so I would think that is not the problem. The elbow I refer to is an easy fix. Good luck.

 

The Pcv elbow isn't dry rotted and valve is working, and i replaced both upstream o2 sensors

 

I fixed the exact same codes on my truck for a grand total of $7. Buy 2 cans of carb cleaner, 1 if there not on sale. And while the truck is running spray any vacuum hoses, intake manifold meeting points, throttle body gasket points and Most importantly pcv and vacuum lines. Listen for the increase in RPMs. It won’t be significant. Just very small and you have to pay close attention to notice it. But it will be there. You can confirm it by spraying it, letting rpm return to idle and repeating the process until you dial in the location of the vacuum leak. Some may say since it’s an EFI motor that it won’t work but it worked for me and I no longer have those codes. Before I was aware of the havoc the pcv elbows caused on the 4.2 I was clueless. This helped me trace my problem to under the throttle body and then to find the VERY small pin hole in the elbow causing my leak. Good luck

 

Thank you ill tell you if i end up fixing it.

 

Spray and listen only rarely works, the PCM is simply too fast. The more reliable method is to use your scan tool and watch either the short term fuel trims or the upstream O2 sensors voltages. You will see a pronounced spike in those numbers when the flammable spray gets sucked in through an intake leak. This assumes, of course, that the problem is actually due to an intake tract leak which probably accounts for over 90% of the occurrences of this condition. PCV elbows, intake gaskets, and loose/damaged intake air tubes are the usual culprits.

FWIW, the upstream O2 sensors do NOT cause this code pair, they're simply reporting the condition.

 

ProjectsSH089, you are right that the 02 sensors don't cause p0171 and p0174. In my case, I was also getting p1131 and p0133, which indicate faulty 02 sensors. I did the rubber elbow and cleared the codes; p1131 and p0131 came back and when I replaced the 02 sensors I cleared the codes again and the ses light did not illuminate again. It seems these codes are somewhat related and at least for me, the elbow and the 02 sensors needed replacement to get the hated ses light off for good. That doggone light bothers me like an itchy rash.