Fuel pump relays

[Jcomeau85]

Where are all the relays for the fuel system.  I have a 1986 F250 carb 460 manual trans

[ArdWrknTrk]

Have a look in the 1986 EVTM.

https://www.garysgaragemahal.com/1986-evtm.html
Section 18 (pg 95-101) is for the selector and senders
Section 19 (pg 102-107) is the safeties/crank bypass and pump control.
Grounds can be found somewhere in the front of the book.

What problem do you have?

[Jcomeau85]

Rear tank shows empty.  Tank is physically full.  Fuel won’t pump.  

[85lebaront2]

That is a somewhat complex system. one item on the 1986 system, the selector switch changes the big motor driven 6 port valve on the frame near the front tank. The system has two power sources, one is a blue wire with a fusible link that is fed power when cranking the engine from a small stud on the starter relay, the second source and the one that keeps power to the system is an oil pressure switch in the back of the block behind the intake manifold.

Here is a link to the 1986 EVTM on the site: https://www.garysgaragemahal.com/1986-evtm.html

If you take the blue wire off it's stud and touch it to the battery stud on the starter relay, you should be able to hear the selected pump run. Set the selector switch to front or rear and try that test, first if the tank selection was changed, you should hear a "clunk" from the selector valve and a faint whirring noise from the pump followed by a hissing sound from the vapor seperator in the fuel line near the carburetor.

I would try both directions when checking, front and rear tank.

Good luck with it and feel free to ask more if needed.

[viven44]

I have never thought about testing them that way. Take advantage of the "hot when cranking" loop.. Nice tip!!

[85lebaront2]

I came very close to adding a "prime" push button switch to Darth as he wasn't a daily driver and usually needed the carburetor filled for a cold start. Now that I have the MAF/SEFI system, it isn't needed.

[ArdWrknTrk]

But the front tank reads correctly and will drive the truck?

The problem is either the switch valve, or beyond, from what you've just told  me

Try jumpering around the valve, and see if the rear tank works.

[Jcomeau85]

Front tank works.    On the documentation from that link at the top it seems like the selector relay is LH corner behind dash???

[ArdWrknTrk]

There's no selector relay shown, just the switch and the valve...

[Jcomeau85]

IMG_2908.png

[ArdWrknTrk]

You're not looking at the correct diagram for ,1986, dual tanks, electric pumps, 7.5l
.......

These things changed.
Go to the pages I pointed out and find the one that represents your truck.

[viven44]

I have deleted my posts as I wanted to make sure I confirm the 86' is the same as the '84 that I have. I may be giving wrong advice here. I did a quick glance and the 86' does look different. First off the tank selector switch on the dash for an 86' is 6 pin and the 84 I have is only 4 pin.

If you have the 86' wiring you will definitely want to look into the 86 EVTM that Jim and Bill pointed to.

I may be wrong but there may be no tank selector relay on the 86 (and Jim mentioned that as well above and it really does seem that way..)

No more multitasking for me and I'm humbled again that not everyone can keep up with Ford's list of changes and revisions  

[Jcomeau85]

Does the valve also supply power to the rear tank when switched?

[viven44]

No.. power to the tanks flow through the in-cab selector switch based on the EVTM. This is a major difference from the 84' wiring that I am used to.

As shown in the picture below from the 86' EVTM
- When the switch is in the front position, pin 2 on the switch connects internally to pin 1 to supply power to the front tank pump (pin 5 connects to pin 3 which grounds out the rear tank pump)
- when the switch is in the rear position, pin 2 on the switch connects to pin 4 to supply power to the rear tank pump (pin 5 connects to pin 6 which grounds out the front tank pump)

You should definitely make sure when the in-cab switch is switched between front and rear tanks that you hear the frame mounted selector valve operate. It should be a small "clunk" as Bill described. Have someone sit in the cab and you can be under the truck to see if the selector is actually doing something.

You have all the wiring diagrams now. You need to get busy and creative with a jumper wire as Jim said and see where the link is broken.

[viven44]

Thanks for being patient with me. I was completely off-base on this one with knowledge from 84' wiring diagram.

[ArdWrknTrk]

I'm not here to chew anybody's head off.

I may come off as gruff because of how autistic I am, but I don't try to hide any of that.
 I do the best I can, on a phone and about a half hour sleep per night.
Please don't feel that I'm targeting you, Vivek!  🙂

[Jcomeau85]

All good.  You guys are great!! What’s a way I can test the switch with a volt meter?

[ArdWrknTrk]

The dash switch, or the switch valve?

[Jcomeau85]

Sorry.  Dash switch

[ArdWrknTrk]

Okay, give me a minute, because it's hard to Juggle pages and photos into a post from my phone....  👍