Hello everyone. I have dealt with this in my 02 F150 but I need some reassurance. I am posting this in the "van" forum because, well, it's a van. My fuel pressure is as follows: Key On Engine Off the fuel pressure shoots up to 30psi then immediately drops back down to 0psi. However, when it is idling, it gets 30psi. Upon acceleration, it gets 40psi. When I come to a stop, it hold steady at around 32psi. It'll do this time & time again. Starting simple, I replaced the fuel filter with no adieu. My thought is that it is the fuel pressure regulator. They reason I am concerned is because I am experiencing some stumbling upon acceleration. Nothing more. No raw fuel smell, no dying, or anything of that nature. Just at times, a heavy hesitation upon acceleration. Can anyone out there confirm my suspicions of the FPR or point me in the right direction please. Thanks!

 

I do not know what you have as a engine but the fuel pressure sound right for a 19lb injectors.
The dropping back down to zero sounds like maybe a bad check valve.

Can you tell us what year the truck is and what size engine you have?

 

Subford! I'm glad it is you!!!! You helped me immensely on my 88 F150! It is on a 2001 Ford E150 with a 5.4L engine. As aforementioned, the fuel pressure falls from 30psi to 0psi immediately after the pump is done charging.

 

On the fuel pressure immediately drops back down to 0psi.
You either have a bad check valve in the fuel pump module, bad fuel pressure regulator or an open injector.
I do not see any of these causing you to have some stumbling upon acceleration.
They may cause longer cranking before starting however.

To rull out the fuel system on stumbling upon acceleration you might want to put the fuel gauge were you can see it and see what the fuel pressure is when it stumbles.
Or have some one else watch it.

Have you checked for codes?

 

No codes. It is in a van, so I run it with the doghouse off with the fuel pressure gauge in full view. I personally think it could benefit from new plugs. I bought it from an old man who took damn good care of it and serviced I regularly. I've ran Lucas fuel treatment last tank, and then Sea Foam on this tank with no success. Upon the longer cranking, it doesn't take any longer than normal. Just a few spins of the flywheel & it fires right up.

 

Well if those are road fuel pressure readings then the fuel system is OK.
I would look at maybe the TPS or one of the temp sensors, air or water.

 

How would a temp sensor cause "stumbling?"

 

If the temp sensors gave the wrong information to the computer, the computer could use the wrong tables.
It would not give codes because it has no way of telling if the readings are right or not.

 

Sure it does, they're called oxygen sensors. Completely agree that a bad temperature sensor can cause the PCM to deliver an incorrect mixture, but the fuel trims would show that something was wrong. And if the trims were far enough out it would throw a rich/lean code of some flavor.

See attached, the specs are for an '04 Super Duty, but they should be the same as on the OP's '01. Pretty sure he has an issue with the regulator, but of course if pressure is in spec while running that's not likely the issue. Unless, of course, an injector is sticking open.

feo_nuts, you really need to get this thing plugged into a capable scan tool. You need to check to see if there are any pending codes as well as check running fuel trims and misfire counts.

 

Tom & Subford>> today, it was stumbling really bad. It would shudder around 40mph pretty severely. It would also idle rough. So, I put I engaged the parking brake, put it in drive and read the fuel psi. It was idling at 30psi and when I would give it some juice, it would shoot up to 40psi and stay there. With my foot on the brake, and at about 16-1900rpm the engine would shake severely. Almost as if your trying to take off from a stop sign in 3rd gear. I think, and correct me if I am wrong, that a coil is malfunctioning and not throwing a code. I plan to try and get it hooked up to a diagnostics machine tomorrow. Thanks everyone!