Jawsh

As the title says, my truck is throwing a P0171 code. It started dying occasionally a while back, finally threw a code, and I got cracking on working on it. It is not throwing a P0174 which normally goes along with it. I replaced the MAF Sensor for good measure, after I cleaned the old one, replaced the Oxygen Sensors (One of them is a royal pain.), and had started doing some more regular maintenance to make sure everything was looking good, like fuel filter, air filter, and cleaned the throttle body.

Now, onto my main reason for posting, I've done a lot of searching and couldn't quite find a situation like mine. It runs like a champ right now, no dying, no hesitation, no misfires, nothing feels wrong at all, but I'm still getting a P0171 code, no matter how many times I erase the code or unplug the battery. The guy at the local Autozone (Who has helped out so much lately, knowledgeable guy), suggested that I might have a sticky injector, and said I might want to run some Seafoam with the fuel. I put a bottle in the tank, and I've gone through about half of that so far.

With 306K on the ticker, I'm sure there's plenty of buildup in the engine. Seafoam, to the best of my knowledge, works a bit slower than other cleaners in the sense that it doesn't blow off huge chunks of carbon deposits, and just kinda takes it off little by little.

Right now, I'm just looking for suggestions for what might be causing that code to be thrown, even now that the main issue has been taken care of.

Thanks in advance guys (and girls)!

kevhead75

Fuel System:
- Damaged or leaking fuel pulse damper
- Fuel filter plugged or dirty
- Damaged or worn fuel pump
- Leaking fuel pump check valve
- Leaking/contaminated fuel injectors
- Low fuel pressure or running out of fuel
- EVAP canister purge valve is leaking when the canister is clean
- Fuel supply line restricted
- Fuel rail pressure sensor bias
Air Induction System:
- Air leaks after the mass air flow (MAF) sensor
- Vacuum leaks
- PCV system is leaking or the valve is stuck open
- Improperly seated engine oil dipstick
Exhaust System:
- Exhaust leaks in the exhaust manifold gasket or mating gaskets before or near the HO2S
Air Measurement System:
- Damaged or contaminated MAF sensor

Jawsh

Thanks Kev, that gives me some more possibilities. I had a bit of a brainstorm today on my way to lunch. I went to fuel up first, and just after I left the gas station, the CEL came on again, literally within a 20th of a mile. It happened the last time I fueled up, but I just thought it was coincidence. I suddenly thought, wait, if the fuel pump's on it's way out, it might be providing just enough pressure for bank 2 since it's where the fuel is delivered to the fuel rails, but then as the fuel is being used on bank 2, it's dropping the pressure on bank 1, thus causing the code. So, I went and got a new fuel pump ordered, and it's supposed to be here tomorrow. Then, it died on me on my way home as I stopped to get my mail.

I had checked over the FPDM a few days back just to ease my mind, and it's in pristine condition! I was quite honestly expecting the hole in the backside that most people have, mine just had a little dust on it, no cracks, no warping, nothing wrong. I did space it out from the frame when I put it back on, just for good measure.

Anyway, once I get the new pump in, I'll report back in with my results, and hopefully it will help someone else out someday.

s_vares

did you test the fuel pressure with a guage?