1995 - F-150 Fuel Delivery Problems

[Drew Dowdell]

My dad has a 1995 Ford F-150, Standard cab, long-bed, with dual fuel tanks, 4.9 liter inline-6, 5-speed, 4x4

He recently had the electric fuel pumps fail in each tank. First the front one went, he replaced that, then a few weeks later the rear one died so he replaced that one as well. He also replaced the rear fuel tank because he found one for cheap on e-bay.

Now, a month or two later, the rear fuel pump appears to be failing again. When the engine is running on the rear tank, the engine sputters and has no power. Flip the switch to the front tank and the engine immediately goes back to normal. The level of fuel in the tank doesn't have any effect on the symptom. When he pulled the tanks and fuel filters, he said they looked sparkling clean inside, as if they were brand new.

He doesn't believe it to be a clogged line issue because when he replaced the pumps, the condition went away, only to return a few weeks later.

He has also recently replace the fuel pump switch relay to no avail.

He says he gets a check engine line sometimes at highway speeds when running on the rear tank (my guess is that it is a "Lean Condition" code) but that it goes away when he slows down.

The truck has about 300k miles on it.

My ideas that I suggested to him, but he hasn't tried yet:

Check the fuel flow out of each tank.

Check the fuel flow at the Y-valve where the fuel lines from both tanks join in to one. (he's not sure if there are disconnects in this section)

Any other ideas?

[balthazar]

Seems like good suggestions.
Not sure how one safely checks fuel flow at the PSI FI engines run at.
Replacement pump certainly may be bad, too.

[Drew Dowdell]

From what I've found online, all Ford engines EXCEPT the 4.9 run at 39psi. The 4.9 runs at ~55PSI. Perhaps he got a fuel pump for the V8?

[Intrepidation]

There are fuel pressure tester kits available at parts stores for around $40. There's a port on the fuel rail to hook them up to.

Also what brand of pump did he replace the originals with? Airtex pumps are hit or miss quality wise, for example.

[balthazar]

I have a older NOS AC Delco in-tank pump left over from my '94, PN 12356976. In the box- never installed. See if that number jives for the 4.9L.

V8 pump theory is worth checking out.

[AAS]

A bit over a year ago Ford dealers got a bad batch of fuel pumps for the 2001 (and related) Mustang GT that we had. Two of those pumps, one purchased in CA and the other a warranty replacement from NM, made it into the car and failed within weeks. Moral of the story... don't rule out the possibility of a bad fuel pump.

[Drew Dowdell]

Update:

He did the pressure test at the fuel rail. My guess seems to have been right. Running on the front tank gives him 50psi (a little low, but more on that later) and running on the rear tank gives him 34psi (a lot low, but even below spec for a V8). So it seems the rear tank is the wrong pump and he might also have a pressure regulator issue. He has a new pump and will be installing that soon.