28 psi fuel pressure on 96 4.0 explorer?

[porshapower]

I did a fuel pressure test today. It was at 28 psi. When I disconnected the vacuum line from the regulator it stayed at 38 psi. I shut the engine off and it sat for 20 minutes with 38psi. Are these numbers low for a 1996 4.0 v6? I am chasing a slight rough idle(stumble) What can cause the low pressure? Pressure regulator? ThanksNelson

 

[ExplorerDMB]

it is a little low -- good pressure is usually 40+ psi. Fuel Filters can be clogged, and the regulator could be crapping out. Whens the last time you changed your filter?

-Drew

 

[porshapower]

Hello Thanks for the reply!!...

New filter a couple of weeks ago. I was leaning toward the fpr. My question is wouldnt the symptoms exist when I drive with a bad fpr?? When I drive the truck it accelerates perfect(slow or fast). Doesnt buck at all even if Im in 5th gear(manual) at 30mph it still accelerates slowly and smoothly. The only things I can think of for low fuel pressure is filter,fpr,pump,obstructed line.... I am thinking of getting a fpr today for the heck of it... Thanks again!! Nel

 

[Green98XLT]

Most fords that I have seen usually run around 40psi with vacumn off and drop to 35-36 with vacumn on. You should not have a 10psi drop with vacumn on/off, or is that a typo?

 

[porshapower]

Did upper manifold gaskets today...

Truck running much better! Havent checked fuel pressure but I will test is tomorrow. Would a upper manifold gasket caused low fuel pressure?? I bought my gasket set at ADVANCED AUTO..they were FELPRO gaskets but I got 6 gaskets and the truck only uses 3. The box says 1996-1997 4.0 v6 upper manifold gasket set QUANTITY:6...?? Any ideas? Thanks!Nel

 

[porshapower]

Yep..there was 10psi increase with the vacuum line off..

The pressure was 28psi with truck running and when I disconnect the fpr vacuum line it was 38psi... I will check tomorrow with the new upper manifold gasket. ThanksNel