Emergency help needed - '87 F150 fuel problem. Fixed!

[sargentrs]

'87 F150 XLT Lariat. 5.0 EFI dual tank setup. Truck just quit driving down the road yesterday. Got it towed to the house. Have about 8 hrs to get it running to get to work tomorrow. Need help guys! I know it's a fuel problem. Tested power to solenoid, distributor, etc and all good. Checked valve stem on fuel rail and getting no fuel. Sprayed ether in throttle body and she tries to start. PO had installed aftermarket electric fuel selector valve via toggle switch on dashboard.

Variables:
Fuel pump relay
Selector valve
Toggle switch
Fuel pumps (2?) and sending units in tanks
Fuel pump on frame rail

Observations:
Tries to run spraying ether in throttle body
Gas gauges work via original toggle switch on dash
Have fuel in both tanks.
Hear both fuel pumps run with key on.

Game plan:
Test relay
Test for power to selector switch
Test for power to frame fuel pump (how do I do this?)
Test for fuel by removing fuel lines from selector valve

Solutions:
Replace relay
Bypass toggle switch to selector valve
Hot wire frame fuel pump
Replace frame fuel pump (already ordered, won't be here until 5:30 pm)

Where/What else? Any and all input is greatly appreciated!

[DuckRyder]

It has in tank pumps AND a frame mounted pump?

How many wires on the frame mounted pump? 2? Power and ground?

[The Bandit]

How about the fuel filter? change it recently?

[sargentrs]

Never changed fuel filter, Bandit. It's on the list.

Duck. 2 wires on the frame fuel pump. I have already verified fuel pump relay is sending power to both tank pumps related to position of toggle switch, up for front tank, down for rear tank. Frame pump is not turning on in any position or key on. Should frame pump also engage with key on or just start position?

[sargentrs]

Located fuel pump inertia switch. Red button not popped. Pulled hot wire from frame pump. Tested in start, only got 8v? Connected fuel pump hot terminal to battery, no noise from fuel pump. Gotta be frame fuel pump?

[DuckRyder]

Why only eight volts?

Grounds?

[sargentrs]

Back up and regroup. Got the pump out and took it up to the battery. Connected staight to battery and fuel pump works. Going to connect a wire under the truck to a good ground and hook the pump back up to the original pwer feed and test again.

[DuckRyder]

A wise man (well at least he had his moments) once told me with any electrical problems, first thing check the fuses, check the grounds.

Clean the ground if you can find it, make a new one if you have to. Worse domes to worse make some jumpers and wire it directly to B+ and see if it runs...

[sargentrs]

Made some jumpers to hook straight to battery. Connected fuel line to rear of pump. Turned on key and can hear tank pump run. Connected jumpers to frame pump and it runs. No fuel coming out of frame pump. When I remove rear line from frame pump, not a heavy stream comes out of line even with tank pump running. Should it be a good heavy stream? It's probably not much more than than a few psi coming out of that line.

[sargentrs]

Is there some kind of valve inside the frame pump? If only 5 psi goes in but 45 psi is supposed to come out, it seems like it would suck itself dry in a second. Therefore, not only does it push the fuel out, once the fuel from the tanks reaches the frame pump, it sucks it in as hard and fast as it pushes it back out. If I can hear/feel it running, but nothings coming out, it obviously has a blockage internally, i.e. bad check valve in the frame pump?

[The Bandit]

I'm not to knowledgeable on these but my thinking is that maybe a check valve somewhere close to the tanks selector valve is stuck close. If it doesnt have some sort of check valve them the full tank will just pump the fuel to the empty tank when it builds up a little pressure.

[DuckRyder]

I'm not to knowledgeable on these but my thinking is that maybe a check valve somewhere close to the tanks selector valve is stuck close. If it doesnt have some sort of check valve them the full tank will just pump the fuel to the empty tank when it builds up a little pressure.

I’m not either, but my guess is that the in tank pump are just lift pumps since it has a frame pump as well...

I am pretty sure the switching valve has the check valves in it. The frame mounted pump may as well, but never seen one cause a no start, just extended crank after sitting...

[sargentrs]

Problem solved! It was the frame mounted pump. New pump came into the parts store at 5:30. Hooked it to the fuel line from the rear tanks selector valve and plugged in the original wiring. Left the output line off and set the end of the pump in a coffee can. Quick bump of the key to "start" and got a burst of fuel. Hooked up the outlet line and she fired right up. Mounted the fuel pump to the frame bracket and replaced the fuel filter. She cranked but didn't want to start. Crawled back under and found the positive terminal loose. Squeezed the terminal tighter and plugged it back in. Took a while for the fuel filter to fill up and fuel to make it to the injectors but she started up and ran great. Apparently the frame pump must have a valve in it or was stopped up to run but no fuel come out. Thanks for the help!

P.S. Sorry if I didn't make it clear, Robert but she was turning over just not starting and running.

[DuckRyder]

Glad you got it going.

I thought later about possible confusion of the “truck runs” vs “fuel pump runs”.

I vaguely recall something about these pumps (usually made by walbro i think) having plastic parts that can fail, so the pump motor running may not directly equal pumping fuel...

[sargentrs]

Thanks, Robert!