Scanner says its P0171 Fuel system bank 1 lean.

I've searched the old posts and most say it is the O2 sensor. My sensors were replaced about 3 months ago when I did my muffler & cat.

any other suggestions?

thanks for your reply!

 

Did you just fill up the tank before the CEL came on?

Usually in a MAP (and not MAF) system like our trucks use, a vacuum leak, clogged fuel filter or weak fuel pump can set that code. Bad gas can sometimes do it to (hence my first fill-up question).

 

No I did not just fill up when the light came on. I usually get my gas at the same place and was at about 1/2 empty when it came on.

I guess a vacuum test is next?

It is running a bit rough at times and wanting to stall. Sometimes idles below 500 RPMs.

 

could be too much air
or too little fuel
or a bad
front o2 sensor

 

Has your problem been solved , with the P0171 code ?

I have the same code that poped up

Have you done a fuel pressure check ? When I put a fuel pressure gauge it read key on (non running ) 46 lbs

after
I started the truck it went up to 49 lbs .
While it was running , warmed up (about 3-4 minutes ) the pressure gage started fluctuating quickly between 44 - 51 lbs .

When you raise the rpms , it steadies out at 49 lbs. I am leaning towards a failing pump .

Does anyone know if something else would make the pressure do this at idle ?

 

49 lbs isn't bad, but it should not fluctuate like that at idle. It should stay steady. A very slight fluctuation, 1 or 2 lbs (ish) up or down for a split second as you raise RPMs is normal, but it should still return to the steady number it was before.

According to the Haynes manual, 35-45 psi is normal. My truck runs at about 48 psi, constant. The fact that yours fluctuates so badly would lead me to think the fuel filter and pump need to be inspected.

 

How did you check your pressure? I thought the 94-97 didn't have a test post since we have the plastic fuel rails.

 

Simply hooked up the fuel gage to the schrader valve on the fuel rail.

This truck has a steel fuel rail assembly on it . I dont know if some have plastic or not .

 

Yeah ,
it stays a steady 49 lbs at start up , then after 3 minutes or so it starts to do the fluctuation real fast . Before this started happening ,I had a slight idle surge after a warm up . Runs good at higher rpms , but now it has a rough idle .

I am thinking the fuel pump is warming up ,wearing out in its design . Pretty sure it is the stock fuel pump .

Thanks for the response

 

If you think it is the fuel pump warming up (which seems a little weird to me) maybe it's a contaminant problem. Run some injector or fuel system cleaner and see what that does. I know with the current Mustangs folks complain about fuels that are high in minerals will foul up the fuel system (I don't remember if it's sulfur or what it is). They recommend running a can of Techron through it and it seems to work for them.