[Stdyhand]

I think my fuel pressure is running low. A key over test is only showing 27 PSI and when I turn the key off it drops to zero in about 5 seconds.

Key on, engine running shows about 32 PSI and drops to 20-25 if I rev up the enigne.

It does run rough at times so I'm thinking the fuel pressure is too low. I changed the fuel filter and that didn't help so I'm thinking its the fuel pump or the regulator.

What is the stock PSI levels?

[MustangMatt96GT]

42 psi if i iirc at idle

[Stdyhand]

Originally Posted by MustangMatt96GT 42 psi if i iirc at idle

What do you think...regulator or pump? Is there any way to test the regulator?

Anything else I might be missing?

[MustangMatt96GT]

I would probably put a 255 lph pump in... chances are thats starting to die, but could be a regulator too, but don't hear about those going out as often

[nolife]

39 PSI with the FPR vacuum line disconnected is the stock base pressure. You can not get an accurate base reading with the vac line attached because the regulator varies pressure based on vacuum, that is why the vac line is there
The only way to "test" the regulator is to watch vacuum and fuel pressure and make sure they track. 0 vac should always be the same as the "base" fuel pressure (0 vac = atmosphere pressure = vac line disconnected) and fuel pressure should lower as vacuum goes up, probably around 30psi with 20in vacuum but that is a guess from what I see on my car. The stock regulator seems to be good quality but are not adjustable, that being said, their is not many times when changing from the stock fuel pressure gives an advantage unless you are tuning and using a specific pressure. I've had several Aeromotive regulators fails over the years but I have an FMU and is hard on them. The most common failure is the internals leaking and fuel pouring into the intake through the vac line.

[flyin ryan]

^^ what he said and i've personally found more power when lowering the base fuel pressure some on a completely stock car but that's not your question.

Typically if the diaphragm in the regular is shit it'll leak gas into the vac line.. so if you yank the vac line from the regulator and it has fuel in it or smells very strongly of fuel then i'd replace it.