Intermintant stalling while Idleing Codes P0171 & P0174

[lazergeek]

Hey guys I wanted to pick your brains on an issue I have been chasing for the last 2 months. It seems to only happen on days over 100 degrees (frequently in Vegas) after it has been driven for a while and is nice and hot.

After it has been ideling for a few minutes it will start idling rough then stall. Sometimes it will throw a P0171 and P0174.

I found a large vacuum leake in the Plenum last weekend and repaired and didnt find anymore leaks.

Today after idleing for 10 min in 108 degree temps it started stalling at idle again. It took 2 min to get restarted at one point and also threw the P0171 and P0174 just before it started stalling. I also noticed the fuel pump was really loud during all this too.

Im suspecting bad fuel pump and tried to rent a Fuel Pressure Guage from Oreillys but had to return becasue it was missing the ford adaptor.
I will have to rent from another store tomarrow.

Any other ideas?

Thanks in advance!

 

[jimbalaya]

I had those same two codes recently and the fix was actually the fuel filter. Here's my understanding of those two codes: the fuel mixture is too lean on both sides of engine, meaning that the system is providing the maximum adjustment to increase fuel mixture and it's still not enough to correct the situation - that's what triggers those codes. This means one of two thing is happening: the vacuum leak is so great the adjustment cannot compensate enough to balance fuel mixture, or the fuel system components are not delivering enough fuel. if you are sure you have fixed all vacuum leaks, then I you've gotta investigate the fuel delivery system, as you have mentioned. My point is that if the fuel filter is clogged, as was mine, replacing the fuel pump will not resolve the situation. The fuel filter is the cheaper and easier fix, so you might want to try that first, especially if it has not been changed in a long time. Having said that, the rough idle is more likely to be a symptom of a vacuum leak [or faulty idle control valve]. Not sure why the high air temps trigger the symptoms.

 

[2000StreetRod]

weak fuel pump?

I suspect that your fuel pump is weak and you should check the pressure. The fuel flowing thru the pump cools it. On hot days the fuel is warmer and doesn't cool a weak pump enough. I am convinced that neglecting replacing the fuel filter at the suggested 50,000 mile interval significantly decreases the service life of the fuel pump.

 

[lazergeek]

I Changed the Fuel Filter and Pump today. Seems to be much better since it was 118 degrees today with no issues. My Wife did say it stalled once when I left her in the car idleing this evening. Didnt throw a code and didnt happen again like it did previously