Engine starved for fuel at low rpms

[dennisb]

   85 f150 351 HO with engine bay mounted electric fuel pump seems starved for fuel once at operating temp on long trips, short runs not so much,(Napa fuel pump is new), when this first started happening I was able to rectify it by switching tanks but not anymore, I also do not see the frame mounted vacuum tank switch on my truck all I see is what looks like an inline pump? Any observations would be appreciated. front tank does not register on gage.
Thank you.

[ArdWrknTrk]

Well, there should be no frame or engine bay mounted electric pump.
Your '85 would have had in-tank electric pumps with a frame mounted switch valve.

Likely there is a suction leak. Electric pumps work much better submerged, and only pushing fuel.

Are you looking to return this to factory?
Or only cobble it together?

[ArdWrknTrk]

On examination, I don't see that Gary has any 351 fuel systems posted from the '85 EVTM. (only 302 & 460) so I can't direct you to a schematic or diagram.

Sorry....

[dennisb]

  Thanks for the quick reply, I'd just as soon keep the new electric pump if it'll do the job? How can I test the tank pumps? Or could the suction problem be coming from elsewhere?

[ArdWrknTrk]

If there is even a tiny pinhole the pump will lose prime and 'suck wind'

Gary said the lines in his truck were like jello.

I will see if I can find a 351 HO diagram for your year.
Gary has a massive shelf full of EVTM's, and posts some pages on this site.

But if you intend to keep the truck, $15-20 for a copy is a tremendous investment in your sanity.
You can find them used on eBay.



 autocorrect

[dennisb]

Cobble for now I guess.
Thank you.

[dennisb]

Thank you, where can I purchase?

[Gary Lewis]

Jim - I don't think the 351's had electric pumps.  Just mechanical.

In the schematic below it says that this is the wiring for "Except 7.5L with dual fuel tanks and electric pumps and 5.0L EFI Engine.  All others had mechanical pumps.

So Dennis' setup is not stock.

[ArdWrknTrk]

His first post says HE has an electric pump mounted...

I'm not saying it is stock.
I'm just trying to figure out how it's wired.

But if the fuel lines look like licorice from Halloween three years ago they need replacement.

I wonder why someone abandoned the mechanical pump?
If the cam eccentric is gone, going back to stock suddenly became a much bigger job.

[Gary Lewis]

I misunderstood.  Thought you were looking for 351HO wiring.

Anyway, it is going to be fun unraveling that.  

[ArdWrknTrk]

Well, he has a new NAPA pump and says sometimes switching tanks back and forth frees it up.

Perhaps there is a lot of sediment, and it gets packed around the filter sock?

I think I would A) try the pump sucking from a bucket or jug and check the volume it's putting out.
B) I'd also drop my endoscope in the tank for a look around.

There must be a switching valve inside the frame rail beneath the driver.
I would probably replace the frame mounted fuel filter as a matter of course.