It's almost like I'm losing pressure in the fuel injection system somewhere. If I let the rig sit a while and turn the key to "on", the electric fuel pump runs for several minutes and then shuts off, as if it's building up pressure in the system. The engine then starts and runs fine.

If the engine has been running a while, and I shut it off, and then immediately re-start it, the electric fuel pump runs just a couple seconds and shuts off. And then the engine starts and runs fine.

Crazy huh??????? Is my electric fuel pump going bad?

 

Change your fuel filter. Sounds like it might be clogged. Even if it's not, a new fuel filter is a good idea anyway and it's only $20 and a few minutes to swap.

Brad

 

Hi Brad,

I changed the fuel filter about 5K miles ago, but I just bought a new one. Gotta work until 9:30 tonight, but I'll install it tomorrow morning.

Thanks for replying,
Tom

 

Thank you all for your inputs. Here's an update:

I put in a new fuel filter today, but that yielded no change in my symptoms. Fuel pump still ran for several minutes with key "on".

No mention of a "fuel pressure sensor" in any of my Ford books. Only a "fuel pressure regulator" that I replaced about 5K miles ago. It checked out OK now though.

My son is a mechanic at Ford, but he's a young guy---and says that he has not worked on an older rig like mine (ouch). He's gonna ask the "older guys" in the shop if they have any ideas.

Anyway, I hooked up a fuel pressure gauge again last night, left it hooked to the fuel rail overnight, and here's what I got:

Fuel pressure with key "off", after rig sitting idle overnight: about 5 PSI, maybe a bit less.

Key to "on": gauge moved slowly from 5 PSI up to about 30 PSI, but fuel pump continued running.

Fuel pump eventually stopped running after about 11 minutes at a little over 30 PSI. The engine then started and ran fine.

About thirty-forty minutes later, pressure had dropped to about 20 PSI.

About five hours later pressure had dropped to about 5 PSI. It has held steady at about 5 PSI.

(One very strange thing happened this afternoon while I was doing fuel pressure tests. On one occasion, after the fuel pump had stopped running after pressure reached about 30 PSI, it started running again! With nothing at all being touched!)

Tom

 

Do you have dual tanks? If so, check your fuel tank selector valve as the seals in it may be weakening.

 

maybe the pump IS going bad, kinda seems like the gas is escaping back past the pump, maybe the little oneway valve in the pump is leaking, not allowing the pump to hold a consistent pressure......im no expert on electric fuel pumps but thats sounds like a possibility to me.....i had a chebbie for a short time that the electric fuel pump did something similar, sounded like it was running longer than it needed too, then the truck got harder to start when cold, next thing you know im stuck at a gas station with a 16' trailor loaded with 2000 feet of conduit and a ditchwitch, and no way of moving the truck, after finding someone to haul my trailor and calling a wrecker i got it back to the shop where i changed the pump,had to drop the tank which was just filled with gas to the brim.....fun stuff.....needless to say i sent the chebbie back to where it came from, put my ford back on the road and havent looked back!!!!!!

 

Did you bleed the system when you replaced the refugulator/filter etc?
Tex

 

Yup, sure did. I bled the system each time.

 

It may be your fuel pump or the check valve in the system. I have approximately 42 psig at the schraeder valve. If you're loosing pressure it's the check valve or fuel pump. Sounds like everything else was done perfectly.

Tex

 

You didn't specify what year your truck is, but here's my guess. If it's the early to mid 90's with the high pressure pump in the tank it sounds like the check valve in the pump module is bad allowing pressure to leak back into the tank when the pump is off. It could also be the regulator even though you just installed a new one. That's what your testing data indicates. To find out for sure you can plug the return line to the tank, install a gauge on the rail and monitor what happens. If you still lose pressure it is the check valve, if you don't lose pressure it is the regulator. The pump module in the tank is only replaceable as a unit. At discount parts stores prices start at around $130.
DannyP

 

Hi Tex94F250 and DannyP,

The chassis is a 1992, so I have the high pressure pump inside the tank. I'll have to try plugging the return line and see what happens to the fuel pressure.

Thanks,
Tom Norman

 

UPDATE:

The verdict came in today, and it was a bad PCM. After a new PCM was installed it started immediately and ran like a top, just like it used to!

Thank you all for ALL your help on this!!!