Hey all, New member here and first time truck owner. Although not nearly my first Ford. I'd like to introduce myself. I'm Alex, I just bought a decently clean 1985 F250-HD XLT Lariat Explorer 2wd Extended Cab 460. I bought it cheap (450!) Cause it didn't start. Well it needed a solenoid so I had one lying around I put on. Then it wouldn't fire, traced it to both fuel pumps not working so I bought one for the midship tank.

Now, it will start up if I pump the gas before cranking, run for a couple seconds then die. I can't keep it running with the gas pedal. Truck was last tabbed 4/2014 and has 103,000 miles. I'm assuming it needs a tune up as well as the carb cleaned out...but does anyone here think it could be anything besides that?

 

I am a six cylinder guy, Alex, so will not attempt to guide you, but wanted to welcome you to the forum!

 

Sounds like your pumps are still not working. That's a common problem with the 460 trucks with the electric pumps. The get power directly during cranking, but get power through a relay controlled by a oil pressure switch after the keyswitch is let go to the run position.

 

Ok, I did notice the pump not getting power after cranking is done. So I should have power with the key on at the fuel pump correct?

So I'll look for power at the relay, if I have power there then I'll check the oil pressure switch. Am I on the right track? If my research is correct it goes Solenoid - relay - inertia switch - oil pressure switch - fuel pumps. Correct?

 

No. In this system, to prime it they took power directly from the starter relay on the fender. So you will only have power at the pump when the starter is turning.

No. The solenoid has a little terminal with a wire that feeds the pumps directly. That's the priming wiring.

I will have to look again to see where the relay gets power, but you are mostly right on that part, relay gets power from somewhere else, but the oil pressure switch activated the coil of the relay and then the relay passes the power on to the fuel pumps.

 

Here's a diagram I got out of a Haynes book. You were right, the relay does get it's power from the solenoid through a fusible link. Which is basically battery power.

 

This helps a lot. Thanks!

I'm still a bit confused, I know the pump is used for priming but is it not the primary pump after the truck has started? Should the pump lose power after cranking?

 

There is one pump per fuel tank, inside the fuel tank. To make sure the carb gets fuel during cranking, they power the pump from a terminal on the starter(I think my diagram may be wrong, there is a small terminal for this).

Once the engine starts, you let off the key the fuel pump loses power from the starting circuit, but gets it back again from the relay circuit. They did this so the pumps will not run if the engine is not running. They know the engine is running from the oil pressure switch. If you are in a accident and you get knocked out and leave the key on, and a fuel line gets cut in the accident, the fuel pumps won't empty the gas tank onto the accident scene because the engine has stalled and has lost oil pressure, which stops the pump.

 

Okay, so they will have power but only after the engine has oil pressure. Now it makes sense. So really I just need to start replacing parts and see what does it, since the prices only have power when it's running I can't exactly diagnose it if it doesn't run. I have a friend with an efi 460 87 I'll see if his relays are the same, if they are I'll try them. Thanks for your help again.

 

There is a 15a fuse on the oil pressure switch circuit. MIGHT be #18. Wouldn't it be nice if it could be that simple!

You can disconnect the oil pressure switch and should have power on one wire WITH the key ON. You can also stick A jumper wire in the plug and bypass the oil pressure switch altogether. But then if you loose oil pressure you could ruin your motor with this safety feature disabled.

That is assuming of course your getting power for the fuel pumps...

The primary fuel pump circuit power comes directly off the big hot lug of the starter solenoid. MIGHT be a yellow and black wire. First possible point of failure is the (20 gauge?) fusible link which is located right at the starter solenoid.

Then the power goes through the inertia switch, which you can also disconnect, jump, and thus bypass.

Then the power goes to the fuel pump relay and waits until the pull down signal comes from the oil pressure switch. This closes the relay and sends the power through a step down resistor wire and then...to the fuel pump (actually you may have a tank switch in there too. I only have a single tank)

The priming circuit power comes off the small lug on the starter solenoid (the "I" terminal if I recall correctly) via a fusible link and taps into the fuel pump wiring AFTER the step down resister wire and feeds the pump full battery voltage.

SO, when the fuel pumps are operating on the main power circuit they are getting something like 7 or 8 volts (through the resistor wire) BUT when it is receiving power from the priming circuit they are receiving 12+ volts. The important thing about this is you do not want to jump power to the pumps via the priming circuit for very long because you run the risk of burning up the wiring or the pumps with the extra voltage.

Also, if you need to replace the fusible links, use the correct specified gauge.

 

Great info. Somebody in Ford's engineering department got pretty creative with this system it seems haha. I'm on my way to test stuff out now, I'll report back when I find the culprit! Thanks again.

 

Ok, I first bypassed the oil pressure switch and the pump doesn't have power after cranking. Then I jumped the inertia switch, and still the pump loses power after cranking. When I unplug and plug in the fuel pump relay I can hear it clicking, so I'm not sure if I should buy a new one or not. Otherwise I'm not sure what else to look at.

 

So I found a fuseable link hiding near the solenoid, hooked it to the positive side of the solenoid and the pumps came on. The truck started and ran good, but when I shut it down the rear tank stayed on even with the key out, but the front pump turned off.

 

Is the primary fuel pump power wire attached to the big hot lug of the starter solenoid yellow and black?

Whatever color it is, it feeds into the fuel pump relay and should be hot at the fuel pump relay at all times.

Use a test light or volt meter to verify you have power on this wire at the fuel pump relay even with the key off.

 

What color is the wire? If it's pink and black it's probably the power supply for the priming circuit and belongs on the little I terminal of the starter solenoid and should only get power while you're cranking.