P0171/P0174

[Kevmobile]

I just bought a 01 Navigator with 130k miles... Been stting since 2016. I just replaced the fuel pump with a Delphi unit. I did not drop/clean the tank. I am getting 171/174. Something to note here is that the fuel gauge turns off/on.

At idle, bank 2 is very lean around +20 LTFT . At idle bank 1 is around +/- 5% for both LTFT/STFT.

On WOT, bank 2 is +/- 4% both both LTFT and STFT. At WOT, bank 1 leans out.

At cruising, they are both lean. If I let off the gas after WOT suddenly it sputters and backfires. Sometimes the fuel trims go to +50% after WOT/Cruising and letting off gas!!!

Something else to note is the Catalytic converters were taken off and you can see both O2 sensors under the truck (they are still screwed into the exhaust pipes).

Also, something else to note is that it only takes 5gal of gas at a time. I replaced the fuel filler neck, but did not touch the evap system lines. Would this be related?

I have never seen anything similar to this where the lean condition jumps b/w each bank based on the load..

Any ideas from anyone?

 

[Hamfisted]

I'd invest in a mechanics smoke machine to properly troubleshoot this issue. Push some smoke through the intake system and find the leaks fast and easy.


Mechanics Smoke Machine on Amazon








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[Kevmobile]

Hamfisted, that is my next step here; however any vacuum leak I have dealt with has been the exact opposite as what I am experiencing here.

With every vacuum leak I have encountered, it has been lean at idle and fine at a load. My issue is lean under a load and OK at idle..

 

[tyasco]

Just joined to share my experience. Got P0171 even though running fine. Replaced MAF, cleared code, but came back with P0174 as well. Pulled intake covers off, found some disintegrated vacuum hoses, replaced them as well as PCV. Cleared codes, no more problems.

 

[jr1under]

Something to note here is that the fuel gauge turns off/on.

Also, something else to note is that it only takes 5gal of gas at a time.

The most likely suspects have already been named but I once had the above two symptoms on my wife's F150 and it turned out that a rodent had chewed a hole in the vent hose above the tank.

It was easy to get this picture of the top of the F150's tank but I can't find a place to take one of the Expedition's.