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OT: F-350 fuel pump electrical issue

T

tjdub

Member
1989 F-350 with a 460.

When I turn the ignition on, the relay clicks, but the fuel pumps don't run. If I take the relay out and jump it with a wire, the pumps run (and the truck runs). I picked up a new relay just in case that's it, but I think it's a fuel pressure switch that's not working. The parts store said it's a $80 part but he didn't know where it was located. I don't see anything around the fuel injector rail that looks like a pressure switch. Is it in the tank?
 
If the relay clicks you are getting the circuit through anything like a pressure switch etc. Its a bad relay ie the contacts inside the relay are junk or the connectors are junked up.
 
Thanks Ken. *fingers crossed*.

I was just a little confused as to why normally when you turn the ignition switch on that the pumps run for a few seconds then shut off. I though there was some pressure switch that flipped the pumps back off when the system was charged. However it looks like this is actually just a dummy "timed delay" feature inside the relay switch?
 
The time delay ,,is in the PCM,it controls the ground cicrcuit to the relay to turn it on or off after so many seconds or if it see's no RPM input .
 
> The time delay ,,is in the PCM

Oh boy. So if it's not the relay, then the computer is shutting down the fuel pumps for some reason. I sure hope it's the relay now because I'm really not looking forward to trying to reason with a computer about this :)
 
have you tried resetting the inertia switch?
it cuts off fuel pump in case of accident...slamming the door sometimes is enuff to trip one...been awhile since i read a schematic but i think the IS is tied in with the ground going to the processor,so in theory the pump would run when you jump the fuel pump relay.

switch used to be behind passenger side kick panel...but ford may have had another ideeeere since i retired in '86
when you find it,if resetting doesnt help,try jumping across inertia switch leads...they go bad sometimes...be sure and replace it if bad because it is important to have fuel pump quit in case of accident.
 
yes, check the inerta switch! i've seen them corrode inside . your's should be on the passagers side floor board, right where the top of the carpet starts

unplug it and jump around it, then try it again.
 

Thanks BCnT and toadady. I'll check that out.

Is there just a button on that inertia switch to reset it if it's tripped?
 
No if the relay clicks its being sent power. Relays only have two states, on or off and that click is the noise of it switching between on and off.

If it switches, and no power gets through, the relay contacts, power wiring to the pump or the pump is bad. You've already ruled out the pump being bad.
 
The pump relay also relies on engine oil pressure to keep it going. In the event there"s an accident and the engine dies, no oil pressure after 5-6 seconds will turn the relay off. Make sure when you"ve got it bypassed and running, you have an oil pressure reading on the gauge or idiot light is out.
 
If it worked jumping twelve volts make sure all your connections and ground are good(clean). Charged battery etc.

I've had similar problems when I had 10+volts or less at the relay.
 
(quoted from post at 18:34:30 03/09/11) 1989 F-350 with a 460.

When I turn the ignition on, the relay clicks, but the fuel pumps don't run. If I take the relay out and jump it with a wire, the pumps run (and the truck runs). I picked up a new relay just in case that's it, but I think it's a fuel pressure switch that's not working. The parts store said it's a $80 part but he didn't know where it was located. I don't see anything around the fuel injector rail that looks like a pressure switch. Is it in the tank?
Click to expand...

99% sure its the relay,,, yours don't use a OP switch are a pressure switch,,, roll over switch is good are it would not run at all... Replaced a FP relay this week on a 88,,, I have only seen a few fail... I had to dig for my tester (old relay with the contacts soldered together),, also have one that I cut open so I could see the contacts close are manually close them if needed... A very simple system and EZ to work on... BTW you can swap the main EFI relay for the FP relay are vice-a-versa... I had a motor home that sit most of the time, once a year it would no-start ,, PIZZ ants somehow would get into the EFI are FP relay...
 
Ken, you win the prize (Note: prize is not an actual prize). I popped the new relay in and all was well.

Thanks to everyone for all the info. I have a much better understanding of how this truck is wired now. They way things have been going, I'll need the knowledge before too long :)
 
Hobo's right. There is no oil or fuel pressure switch, only an inertia switch that opens in the event of a crash. It's after the pump relay. The PCM only engages the pump relay in crank mode or when a PIP signal is detected. (running engine)
 
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