Fuel Circuitry problem - 1990 F150
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Joined: Nov 2000
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From: Calgary
Fuel Circuitry problem - 1990 F150
Ok, here it goes.
The rear pump on my truck is almost dead (barely keeps the truck idling) so I rely on the front one. Well the front one died today, I removed it and hot-wired it and it does work.
Checked for power at the connection for the front pump, not enough for test light, but multi-meter picks up some power. And when I test the switch inside the cab, the test light picks up nothing, but multi-meter does. I messed around in there once, and thought there was enough juice (12v?) to run a test light?
Pulled off relay and tried hot-wiring the wires - with switch on back tank, i can get the pump to work. With switch on front tank, the pump doesn't work, but I hear the plug "clicking".
It seems that If i switch the back tank's plug to the front tank, then front tank would work. I checked the wiring, nothing looks broken at all.
I'm going to get a new relay tomorrow morning. I could only find 2 relays under the hood above the fender, one for fuel, one for ??
Sorry if i'm not making much sense, it's been a long day.
Maybe if anyone's gone through something like this they could give me a shout.
Jason
1990 F150 4x4 302 5spd
The rear pump on my truck is almost dead (barely keeps the truck idling) so I rely on the front one. Well the front one died today, I removed it and hot-wired it and it does work.
Checked for power at the connection for the front pump, not enough for test light, but multi-meter picks up some power. And when I test the switch inside the cab, the test light picks up nothing, but multi-meter does. I messed around in there once, and thought there was enough juice (12v?) to run a test light?
Pulled off relay and tried hot-wiring the wires - with switch on back tank, i can get the pump to work. With switch on front tank, the pump doesn't work, but I hear the plug "clicking".
It seems that If i switch the back tank's plug to the front tank, then front tank would work. I checked the wiring, nothing looks broken at all.
I'm going to get a new relay tomorrow morning. I could only find 2 relays under the hood above the fender, one for fuel, one for ??
Sorry if i'm not making much sense, it's been a long day.
Maybe if anyone's gone through something like this they could give me a shout.Jason
1990 F150 4x4 302 5spd
Senior User
Joined: Feb 2000
Posts: 390
Likes: 1
From: South East Alabama
Fuel Circuitry problem - 1990 F150
I read a few years ago about a guy with a truck just about your vintage with the same trouble and symptoms. Long story short. They ended up taking a test light with the sharp point. Located the hot lead going from the fuse/relay box under the hood down to the frame and on back to the tanks.
As they probed the wire with the test light they found about two feet down the hot lead that: Although it looked great on the outside, inside the insulation the wire had corroded and turned to powder. Causing the intermitten problem. The wire was MUCH cheaper than a fuel pump and easier to replace. Good Luck. Hope this helps.
Chris
As they probed the wire with the test light they found about two feet down the hot lead that: Although it looked great on the outside, inside the insulation the wire had corroded and turned to powder. Causing the intermitten problem. The wire was MUCH cheaper than a fuel pump and easier to replace. Good Luck. Hope this helps.
Chris
Post Fiend
Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
Fuel Circuitry problem - 1990 F150
The other relay is the EEC PWR relay, and it sends power to ALL the sensors & injectors AND to the FP relay. Try running a power wire directly to each pump (and a ground off each one, of course) and see if they run. If they do, it's definitely a wiring problem. Bypass each component with a hot wire to find out which one is open.
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