I have an 84 ford f250 with a 460 and dual tanks. I turn the key on and neither of the pumps are getting any power. both pumps are good, I tested them. we Changed the fuel relay and still no power to either of the pumps. I retraced all the wiring from the battery to the relay to the pumps and everything seems to be exactly as it should be. What could Possibly be my problem??

I also have a few other Questions. Does this truck regulate the fuel through oil preasure like the single tank truck or is it through the tank selector valve? I was also considering just taking the tank selector valve out of the system and rewiring the truck as if it were a single tank truck and just running it off the front tank. would that be as easy as running the wires from the front tank to a new single tank relay?

Please if anyone has any answers for me i would appreciate your help.

Thank you!

 

I assume that you have the "hot fuel" option with pumps and sending unit in the tanks, if so that opens up several possibilities. If so, the pumps and sending units get power through the fuel selector valve, so if that goes bad ($300 from the dealer) you're stuck replacing it. Or re-engineering the system to work without the valve.

An easy way to test is have someone in the cab with the key to the run position flip the switch on the dash while your under the truck and you should be able to hear the valve switch between front and rear. They were also bad about the switch on the dash going bad and that would cause a similar issue, and much cheaper to replace.

You say you tested the pumps, might I ask how you did that? Do the sending units have 3 pins in a triangular configuration, or 4 pins in an oval, that will determine which sending units you have.

On mine, with a manual transmission, I have to push in on the clutch and turn the key to the start position to get the pumps to energize, unlike a newer fuel injected vehicles when the pumps energize in the run position.

There is also the inertia switch located on the passenger side up by the transmission, and a separate oil pressure switch located at the back of the engine that feeds to the inertia switch.

Assuming the "hot fuel" option there is a divertor valve up next to the coil that sends unused fuel back to the tank and acts as a manual pressure valve (that's over simplified, but the basic premise) supplying fresh cool fuel continually to the carburetor.

From personal experience these things can be a nightmare to diagnose and fix. Maybe someone more educated here can offer some other suggestions of things to check, or correct me if I missed something. (Been interrupted about 5 times here at work trying to type this up).

Elemak

 

Since you Have Electric pumps there is a wire off the oil pressure sending unit that sends juice to the pumps

 

There is also a "priming" wire at the starter relay, it is a blue fusible link. You can jumper that to the battery terminal to test the pumps. On 86 models it also powers the tank selector valve.

 

Power for the fuel pumps does not go through the selector valve, only the sending units go through the selector valve.

The oil pressure switch powers the relay, not the pumps. The relay powers the pumps, through a safety switch that may need to be reset.

And they are correct, this system only sends power during cranking and when the engine is running.

 

Thanks Dave, I thought you had the diagram for the 84 model.

 

I know this is an old post but the information is a good starting point for me without digging through 6 pages of random points.

I see my oil pressure sending unit it and it is attached and right next to it is a 2 pin plug that is jumped out. Does that mean the OPS is bypassed?

I have 12 volts at the yellow wire on the fuel relay. So my inertia switch is good.


My next step would to be either jump out the OPS wire straight to battery or jump the pink wire off the starter relay straight to 12v. Which would give me a better result?

Correct me if I am wrong but if the relays are good either of those options should make the in tank pump start? Or do I still have to troubleshoot the tank selector as mine has wiring to it as well.

Good thing for me I do not have a bed on my truck so access is easier.

 

If the OPS is jumpered you should be getting power to the fuel pump cutoff relay when the key is on. The relay should give an audible click when it activates. At this point the pink with a black hash wire should be live, it will have 12 volts at the cutoff relay end, and if nothing beyond it is good 12 volts going into the tank selector relay.

If you take the blue fusible link from the terminal labeled "I" on the starter relay and hook it to 12 volts you will be putting power directly into the tank selector relay. In order to test both pumps you will have to have a working tank selector switch to change the tank selector relay. If you simply want to test each pump by itself, power either the red wire for the front tank or brown with white stripe wire for the rear tank. Don't run it too long as whichever tank the selector valve is on, is where the return fuel will go.

 

Let me just clarify the tank selector relay is the other relay under the hood next to the green fuel relay?

The drawing above also shows another tank selector valve/relay, should I even be worried about that portion yet? or just worry about the two relays under the hood?

 

The tank selector valve/relay is on the frame rail alongside to forward tank. It should sort of whirr as it moves since it is motorised. Unless your truck happens to be a dually, which I doubt since you say 4X4, then yes, those are the relays, tank selector and pump.

 

yep, found it. I just wanted to make sure that there are two parts that are called tank selector relay as the drawing above shows two components with that name. I will start testing tomorrow and provide feedback as i get it.

quick question. I am looking at my fuse panel and comparing it to the above schematic. The schematic says the OPS wire goes through a fuse at location 18. My fuse block doesn't show an 18 only goes to 17.

First step tomorrow is place the key switch in run and test for 12v at the bypassed OPS.
(I have already verified that the cutoff relay has power at the yellow wire).
Then move to the relay and back pin the ops wire and see if it is present there. ( I know the ground wire is grounded as I redid that wire to a clean ground.)

This should cause the relay to click and close, which will push 12v on the pink wire to the tank selector relay.

This relay will be made when 12v is applied to the other leg of the coil. the wiring diagram shows 2 Brown/w wires. (one to rear pump other to selector switch)

Once i decipher which wire is not the rear pump that needs 12v applied so the relay makes and passes the 12v on the pink wire to the associated pump.

Please let me know if my train of thought is correct.

After that I can test the actual tank select switch.

 

Is this "hot" fuel system an option or engine/weight related thing?
I'm confused, my '85 is gravity fed.

 

The "hot fuel handling package is equipment and probably location related.

 

It's mostly on 460 equipped trucks. I have heard there may have been some 351w's with it but if there was it wasn't many.

Your is not gravity, it has a fuel pump. Unless you have your fuel tank mounted on top of the cab.

 

Gravity out of the tank and through the relay, there be a mechanical pumper up front for sure. 460 thing, good to know. thanks

Or maybe siphon is a better term, I can say that when the plastic line breaks between the relay and the pump the rear tank drains completely.