Fuel Pressure Dropoff

[rtaylor0]

Hello Everyone,

So, I recently purchased a 1997 Ford Explorer XLT 4x4 (4.0L SOHC). Anyways, I'll give you a little background here. I bought the vehicle and shortly after I got check engine lights for P0171 and P0174 (Which means it's running lean). My first impression was to change the fuel filter so I did. I then learned that the PCV elbow can sometimes be bad so I checked that and it was fine. I took it to a mechanic who replaced the intake manifold gaskets but it still has the same problem. I tried replacing the upstream oxygen sensors but that didn't fix the problem either. Following that I tried cleaning the MAF sensor, still with same problem.

So, anyways to get the vehicle to start I have to prime it a couple times otherwise it cranks for a long time. So, I got a fuel pressure test kit to test the fuel pressure. When the vehicle was running it ran at a constant 30psi but when I turned off the vehicle it slowly dropped off to 0psi. So, I figured this must be my problem. But, I'm not sure where to take it from here. Any advice would be greatly appreciated!

 

[J_C]

It dropped to 0 PSI how slowly? If it took a few minutes I wouldn't focus on it, but if it did faster then I'd wonder if your pressure regulator is shot. 30 PSI is at the bottom but still within the range of acceptable fuel pressure, but does it stay that high if engine RPM rises?

You can unplug the vac line to the fuel pressure regulator and hook a vac pump up to see if it holds vac or is leaky. You can put fuel injector cleaner in the gas and drive awhile if it's the in tank check valve or a leaking fuel injector, but if it does turn out to be the check valve then you may need a whole new sending unit and might as well replace the pump too while you're in there.

If it's a leaking injector(s) then you might also see a difference in the spark plugs for those cylinders, either fuel on them or cleaner than the rest.

Other potential sources of leaks include the rubber and metal fuel line itself, the fittings, the fuel rail. Look around for drips, clean areas where gas washed dust away, and the smell of gas.

When you took it to the mechanic did you state "replace my intake gaskets" or "fix my lean problem" ? If the latter, seems like the mechanic needs to make good on the repair.