Is fuel pressure supposed to drop when you rev you car up ?

[jfman]

Is the pressure supposed to drop when you rev you car up? I am getting 31-34lbs at idle and drops to 20-23lbs when I rev it up.

Is this normal?

 

[bhuff30]

Fuel pressure varies in direct relation to the pressure in the intake manifold. When the car is off, the fuel pressure should be around 40psi with the fuel pump on. At idle, where there is a vacuum in the manifold, it will be around 31-32psi. As you get into the gas, the fuel pressure will rise, up to about 40psi if you give it enough load. When you let off, the fuel pressure will be the lowest, around 27 psi.

Does the car run fine in normal driving? If so, I'd say everything is fine.

 

[GT Tommy]

Fuel pressure readings!

Is the pressure supposed to drop when you rev you car up? I am getting 31-34lbs at idle and drops to 20-23lbs when I rev it up.

Is this normal?

From what I have been reading, at idle your fuel pressure should be between 35 psi and 40 psi. Most people say that they find their stock GT Mustang engines running really well with these fuel pressure values. When you accellerate or rev up your engine, your fuel pressure should increase, not decrease. I would check on your fuel pressure regulator, and fuel pump. Good luck, Tommy.

 

[jfman]

Yes I am having trouble with stumbling at WOT the motor dies. Thanks for the input guyz. I am going to clean the FPR and if that doesnt work I'll replace the pump.

 

[Don 95Vert]

If you are talking about your Lightning - before you do any of that, check FP at WOT with a gauge - if it drops or does not go up proportionally to boost (1:1 or 39 + boost) then it's probably the high speed fuel pump relay gone bad. I have seen it happen to a lot of Lightnings. The relays are in the small relay box next to the big power dist. box under the hood.

Don

 

[jfman]

It's actualy an f250 with gas engine.

 

[squeak93]

If you just blip the throttle while in park it is possible for the fp to drop just for a moment. If it drops and stays down then you have an issue.

 

[007]

If you are talking about your Lightning - before you do any of that, check FP at WOT with a gauge - if it drops or does not go up proportionally to boost (1:1 or 39 + boost) then it's probably the high speed fuel pump relay gone bad. I have seen it happen to a lot of Lightnings. The relays are in the small relay box next to the big power dist. box under the hood.

Don

I 2nd that. Fuel relays are a common problem with Ford trucks, often making them not start. Happened to my friends old F150.