I've been having a problem with my 1992 460 fuel injected engine, with an in-tank electric fuel pump. When I turn the key to "on" before cranking the engine, the electric fuel pump runs upwards of 11 minutes before shutting off. Items already replaced are the fuel pressure regulator on the FI rail, and the fuel pump relay.

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".

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!)

Any theories? Is my electric fuel pump possessed?

Tom

 

It sounds like the relay is sticking. Replace that, especially if it's the factory green one, and it should be good to go. The fuel pressure is quite low, it should be 30-35 with the engine idling, but upwards of 40-45psi with the engine off and pump on. The pump may be on it's way out.

 

Hi Jared,

Thanks for the input. Looks my fuel pump is crapping out on me. I forgot to mention that this fuel pump is on a F53 motorhome chassis----so that electric pump has to work pretty hard. I've also heard from other motorhome owners that the electric fuel pump on 1990-1994 vintage 460-powered motorhomes was a weak link, with a very high failure rate.

I replaced the fuel pressure regulator about 5K miles ago when the internal diaphram ruptured. I replaced the fuel pump relay the day before yesterday----and the OEM relay was green. I put in a new fuel filter this morning. No change in symptoms.

I left the fuel pressure gauge connected to the injector rail so I can check it periodically. Since I have been experiencing these problems, my fuel pressure has never registered higher than about 30 PSI at idle. It has not registered anywhere near 40-45 PSI with the engine off and the pump on----it has stayed at about 30 PSI, regardless if the engine is running or not.

Thanks again for your input. Looks like I better budget for a new fuel pump?

 

Yes, the pressure is low. About 32 at idle and around 40 with the vacuum line off of the regulator at an idle or with the key on, engine off.
I am wondering if the ecm is bad and not turning off the pump relay after 2sec.
Also, check the ecm ground wire, it should be the smaller ground wire on the - battery cable. If the ecm has a bad ground, it will do some crazy things.
I would look into replacing the pump to get the pressure back where it belongs.

 

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!!!