Fuel Problems...

it might also be your fuel pump itself

when i first purchased my car it would stall when i was slowing down to stop at a light. the computer showed both left and right bank (o2 sensers ) were bad. fuel pump was never niosey turn out that was the culprit it could not hold pressure. if it is hard to start after sitting for a while it could be the pump. check o2 first cheaper if that the prob.

If the pump is noisy, it's probably it. Get a fuel system guage from the autoparts store and see if it has hold pressure. Not only that, you may have a loose or frayed wire somewhere that might be cutting the fuel pump's power sporraticly and sending codes. The O2 sensor codes will come on any time it's lean, so fix the pump problem first and hopefully the O2 codes will go away.

I'd say there might be a good chance that a bad electrical connection could kill your pump from cycling it on and off too much while there is a load placed on it. Gotta be carefull when you get those issues, since they can set off a long chain reaction of problems. I've never messed with our pump relay, I don't even know where it is.

I was getting O2 codes last week and a few days ago I changed the fuel pump and it fixed it. Too bad it didn't fix the EGR valve code

SN95Oh said:

Car:
94 Mustang GT
3.55 Gears
Trickflow intake
Flowmaster exhaust w/ H-pipe

Okay I just recently installed a new intake on my car (trickflow).
And it ran strong for a while and 2 days later, it started running like a dog.
It was cutting out and stalling when idling. I checked for intake/vacuum leaks. I didn't find any... So I did a diagnostics check, and it came up with these codes.
181 - System lean right bank.
556 - Primary Fuel pump relay malfunction.
The fuel pump is pretty noisy. Even after the car is started. I bought a new fuel pump relay. But I have no Idea where the fuel pump relay is located. So I also want to know the location of that thing. Any Ideas?

Click to expand...

Where the hell did you find a SN95 in Oklahoma? (I live in Oklahoma and I am going to be purchasing one in a month or so)

I was about to post almost the exact question when I saw tis one. I am in the process of painting a customers car. But first he wanted to use my paint boothe to do engine work. I have a hydraulic lift to get cars up so I can detail under them.
So we installed Trick Flow twisted wedge heads, Trick Flow intake, 1.7 RR's.Long tube headers and Mac power chamber pipe and flow master 2 1/2" system.
Car runs like crap, have been checking things and posting questions for 2 weeks. Finally ran codes and got a 542, 543, 556 all fuel pump related, then customer says," oh I had a guy install a fuel pump just before I brought you the car" So I decided to finish the paint job and let him take it back to the fuel pump "Guy".
The fuel pump relay on cars up to 93 was under the drivers seat, not sure where they hid it on 94-95's