84 Fuel pump always running
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From: Squaw Valley, CA
84 Fuel pump always running
I was just given a 1984 F250 extended cab, with AC, a 460, C6, and Dana 70 3.53 . I plan on using it as a tow rig, it has low miles and is fairly clean, could use a paint job, but is straight and all so I think it will be a pretty cool tow rig for my car hauler, bumper pull horse trailer, and goose neck horse trailer.
Anyway, I need to put a new carb on it, this one is all messed up. Problem is the fuel pump runs all the time even with the key off. I have never messed with an older ford and was wondering where the fuel pump relay is or any other info on it, or if this is even stock, I would think it would have a mechanical on the side of the block.
Its a dual fuel tank if that make any difference
Also what was the common weak link for the fuel gauge not to work on this era truck.
Thanks
Anyway, I need to put a new carb on it, this one is all messed up. Problem is the fuel pump runs all the time even with the key off. I have never messed with an older ford and was wondering where the fuel pump relay is or any other info on it, or if this is even stock, I would think it would have a mechanical on the side of the block.
Its a dual fuel tank if that make any difference
Also what was the common weak link for the fuel gauge not to work on this era truck.
Thanks
Laughing Gas
Joined: Apr 2013
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I had a problem with the fuel pump running all the time and the problem was with the starter solenoid.
Follow your positive battery cable to locate your starter relay...
Your starter relay should have two small terminals, the I and S terminals. IIRC the starter signal wire is attached to the S terminal and your fuel pump bypass wire is attached to your I terminal.
The I terminal should only be energized while the starter is cranking and it should not be energized at any other time.
You can take a volt meter to check and see if the I terminal is hot all the time, or you can just disconnect the fuel pump bypass wire from the I terminal to see if your fuel pump shuts off.
Try that and let us know how you do.
Follow your positive battery cable to locate your starter relay...
Your starter relay should have two small terminals, the I and S terminals. IIRC the starter signal wire is attached to the S terminal and your fuel pump bypass wire is attached to your I terminal.
The I terminal should only be energized while the starter is cranking and it should not be energized at any other time.
You can take a volt meter to check and see if the I terminal is hot all the time, or you can just disconnect the fuel pump bypass wire from the I terminal to see if your fuel pump shuts off.
Try that and let us know how you do.
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A lot of the 460 equipped trucks did have electric in-tank fuel pumps. I am thinking the fuel pump relay may be mounted on the driver's side in the area of the brake booster. The fuel pump gets power from the relay AND from the point the previous poster described on the solenoid. The solenoid power point sends power during cranking, the relay sends power after the engine is running and is controlled by a oil pressure switch. No oil pressure, no fuel pump power from the relay.
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Ok I discovered if I disconnect this relay the fuel pump will shut off
This black wire was connected to the always hot side of the solenoid, I remove it an and it shuts off the fuel pump
This black wire was connected to the always hot side of the solenoid, I remove it an and it shuts off the fuel pump
Laughing Gas
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That's interesting. There's just no telling what someone may have done to the fuel pump circuit wiring before your got the truck.
I can't tell which relay you disconnected but according to this diagram disconnecting either the fuel pump relay or the fuel tank selector relay (they are often confused) would interrupt the power to the fuel pump...
If it was mine I'd be curious to see if a prior owner had somehow hot wired the oil pressure circuit (which is only supposed to be hot in run or start see fuse #18 in the diagram) and also jumped or bypassed the oil pressure switch (located on the top of the motor all the back toward the firewall).
Either that or the oil pressure switch has been jumped and something in the key switch or ignition switch is causing the oil pressure circuit to remain hot all the time?
Good luck and let us know what you find.
I can't tell which relay you disconnected but according to this diagram disconnecting either the fuel pump relay or the fuel tank selector relay (they are often confused) would interrupt the power to the fuel pump...
If it was mine I'd be curious to see if a prior owner had somehow hot wired the oil pressure circuit (which is only supposed to be hot in run or start see fuse #18 in the diagram) and also jumped or bypassed the oil pressure switch (located on the top of the motor all the back toward the firewall).
Either that or the oil pressure switch has been jumped and something in the key switch or ignition switch is causing the oil pressure circuit to remain hot all the time?
Good luck and let us know what you find.
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From: Squaw Valley, CA
I disconnected the grey relay, not the yellow one. Where should the black wire in my hand go, always hot side or starter side
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Laughing Gas
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Come to think of it, I suppose it's also possible the fuel pump relay could simply be stuck on...
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Laughing Gas
Joined: Apr 2013
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The fuel pump power supply is always hot.
It's the oil pressure circuit that closes the fuel pump relay and allows the power to flow to the fuel pump. The way it's designed: No oil pressure = fuel pump relay remains open, no power to the pump. HOWEVER, it's fairly common to see the oil pressure switch bypassed with a jumper wire and this causes the pump to run with the key in run or start, even if the motor isn't running.
The only other way the fuel pump should get power is via the fuel pump bypass wire that's supposed to be connected to the small I terminal of your starter solenoid. This wire should be energized ONLY when the starter is cranking...I personally had a problem with a starter solenoid sticking and leaving this bypass wire hot all the time. Took me a while to figure that one out! LOL.
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From: Virginia
Always hot, same lug as the battery cable.
The fuel pump power supply is always hot.
It's the oil pressure circuit that closes the fuel pump relay and allows the power to flow to the fuel pump. The way it's designed: No oil pressure = fuel pump relay remains open, no power to the pump.
The only other way the fuel pump should get power is via the fuel pump bypass wire that's supposed to be connected to the small I terminal of your starter solenoid.
The fuel pump power supply is always hot.
It's the oil pressure circuit that closes the fuel pump relay and allows the power to flow to the fuel pump. The way it's designed: No oil pressure = fuel pump relay remains open, no power to the pump.
The only other way the fuel pump should get power is via the fuel pump bypass wire that's supposed to be connected to the small I terminal of your starter solenoid.
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From: Squaw Valley, CA
Well tapped on the relay and now the fuel pump does not run 24/7.
I guess it ran out of gas riding around the property this weekend, will not start at all now. Wish Ford gas gauges worked better
Need to put some gas in it and see what happens.
Also need to find a source on a rebuilt carb, or a complete rebuild kit. Was told that before it would run the carb dry/or is not getting enough fuel under a load.
I guess it ran out of gas riding around the property this weekend, will not start at all now. Wish Ford gas gauges worked better
Need to put some gas in it and see what happens.
Also need to find a source on a rebuilt carb, or a complete rebuild kit. Was told that before it would run the carb dry/or is not getting enough fuel under a load.
Laughing Gas
Joined: Apr 2013
Posts: 1,049
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As for running out of fuel under a load, 1st thing to check are the fuel filter(s).
If it's got the original 4180 carb they aren't that hard to rebuild. Get a genuine Holley rebuild kit, Summitt racing has them for about $40.00 or so, if I recall correctly. Also, if you want new floats you'll need to order them separately as they don't come with the kit.
In addition, you will also need to buy the metallic intake to EGR spacer gasket separately as that doesn't come with the rebuild kit either.
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