How does the fuel system on my 1989 Ford F-150 work?
My 1989 Ford F-150 won't start this morning. The truck seems to not be getting gas. The truck will start but immediately stop running. There's a sound like a pump trying to run after I turn off the key. It runs for 30 seconds or so then intermittent runs until it stops. What is happening?
The fuel system has two pumps… A low pressure pump in the tank and a high pressure pump along the left frame rail below the door. If you have dual tanks, then each tank has a low pressure pump and a selector valve/switch to switch fuel supply. The system gets power and ground from the computer and EEC relay which powers up the fuel pump relay and sends power to the inertia safety shutoff switch and then onto the pumps… Which then ground to the body or frame.
When you first turn the ignition key on, the computer grounds the tan/lt green wire from the coil side of the pump relay to power both of the pumps… In tank and along frame rail… And prime the fuel system for a few seconds. Then shuts off… Once the truck starts running, the computer senses an rpm signal from the distributor, cam or crank sensors depending on model year and powers the pumps again via the pump relay… Which in turn gets power and grounds via the PCM The EEC relay output circuit also controls other items like injectors, etc. If the truck starts and then shuts off, I'd first test for power at the EEC and pump relays… You should hear or feel both relays click when ignition is turned on… And the pump relay should click/shutoff after priming… Then the pump relay will click back on when the truck is running. If you get no ground at pump relay, then check wiring from there to PCM or power in or EEC relay and PCM… Possibly a defective PCM? Or other issue. Bad rpm sensor? You can manually bypass the pump relay by connecting a properly fused power wire from the battery to the brown wire at the pump relay which will power up the pumps… Start truck and see if it stays running. If not, then it might be other issues like rpm sensor, PCM or EEC relay, etc. Check for good grounds for the pumps… Common problem was a bad ground wire connection /corrosion for the pump below the door.
The red wire at the pump relay is the coil side of the relay which gets it's power from the EEC relay… I assume that is OK since the pumps do seem to prime for a few seconds.
You may still have issue with low fuel pressure… A weak high pressure pump, bad pressure regulator or clogged fuel filter, etc… Need to test for proper fuel pressure at engine /pressure regulator.
http://www.fordf150.net/forums/viewtopic.php?t=80501
Fuel system wiring diagram…
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