85 F250, 460 with dual tanks and hot fuel handling. Last time I was home I got her running but she was misfiring badly. This time I did a full tune up and oil change and went to start her up and now I dont have any power going to my fuel pumps. The rear tank is actually out right now but I connected my multimeter and tested the pins on both fuel tank electrical connectors and there is no power to either one no matter what position the front/rear switch is in...the google searching I have done pretty much points to one of two things: either a relay or the inertia switch...I looked all over under the dash for the inertia switch and couldnt find it...even pulled back the left kick panel by the parking brake and looked behind there...where is it???

Relays- there are three on the drivers side...one is on the fender and the other two are on the firewall mounted right below the first one and have a plastic cover over them. Which of these is the fuel pump relay and what are the other two so that when I go back to the autoparts store tomorrow I know which relays I need to buy. I will replace all three. Or are the all the same kind of relay and I can just buy three of the same? One of these is the fuel pump relay right?

 

If the inertia switch is not beside the bellhousing hump you should look behind the passenger side kick panel.
Is your oil pressure sensor properly connected. (not the sender)

But, there should always be power to the pumps when the key is in the 'Start' position.

It is one of the pair of relays.
Certainly no need to be throwing parts at it.
Just swap the existing relays around and see if it changes before you go out buying new ones.

 

Okay so its not the relay...changing it out with a new one did nothing. I found the inertia switch and it wasnt popped. I then tried to run a bypass with a power wire from the battery through a toggle switch...which of the wires on the connector to the pump do I need to run the power to? I have blue/brown, blue/yellow, red, and orange in that order. Pretty sure blue/brown is the ground and I tried tapping power to the red wire and my multimeter showed 12 volts after I did that but still no fuel out of the line...the tank was dropped and cleaned out and the pump replaced last time I was home and it was working. So if the red wire going into the fuel pump isnt power, is it orange? I dont wanna strip the insulation off of any more wires until I know.

 

Have a look at the diagrams Franklin posted in this thread.

https://www.ford-trucks.com/forums/1...el-system.html

You can see how the starter solenoid directly powers the selector relay while cranking.

 

Okay, I checked for power going into the fuel relay, which there is at ~11.5 volts. Then I had a friend turn the key to run and I put my ear by the front/rear selector valve on the frame rail and listened (at one time I thought this was the problem and autozone didnt carry it so I called the local Ford dealer- $360!!! for a new one)...the selector valve is working, which means the switch in the dash isn't the issue either.

Looking at the diagram, it looks like the five pin relay that I replaced, listed as the selector relay (Autozone's computers had it listed as "fuel pump relay"). I checked for power at the plug for the cutoff relay...I have a solid 11.5 volts at the yellow wire from the inertia switch and no power from the oil pressure switch but I assume thats normal since the engine isnt running...

 

Check your starter solonid. There there are two small post. one is form the ing. switch for cranking the other one is a fuseable link that puts power to the relay when cranking. It should be a blue wire. after cranking and good oil pressure then the power thru the intra switch takes over.
also, The wires at the pump/sending units change from power to ground depending what position the tank selector valve is in.
Good luck Rodger

 

The selector valve clicking only proves the dash switch is working.

Follow the diagram and see that power from the yellow inertia wire will only travel through the shutoff relay if the oil pressure sensor pulls it down.

The starter solenoid will power the selector relay(on the firewall) while cranking no matter what.

Probe the brown/white and red wires to ground while cranking and see that one or the other has power.

If not, I'd suggest that there is a problem with the selector relay, or its socket.
Try removing the relay and jumpering the pink/black wire directly to the red wire in the socket.
See if the front pump does or does not work while cranking.

 

I jumpered pink and black to yellow in the relay socket...that only got me six volts on the plug for the pump...shouldn't it be twelve?

 

No, you are not going to do anything jumpering hot to hot.
You see six volts because of the resistor wire that you placed in the circuit.

Look at the diagram...

Remove the SELECTOR relay (right next to the cutoff relay and jumper the pink/black wire (or for that matter any fused, hot wire) to either the front pump (red) wire or the rear pump (brown/white) wire to power the pump directly.

The tank selector valve only switches the fuel gauge sender wires, not the power to the pumps .

 

or if i could locate the oil pressure sensor id just jumper its connector instead...but i couldnt find it

 

It doesn't matter if the oil pressure sensor is in the loop at all while cranking.
That is why I said to check with the key in the 'start' position.

Either the pump will work or not.
If it does, then you have a problem with cutoff circuit.

But you say you get no fuel at all.
Which means the pumps aren't working in the start bypass position either.

So I said to jump the wires in the switching relay.
Which would either prove it bad or send you closer to the pumps looking for a break/bad connection.

Do you understand how to troubleshoot and read a schematic?

 

is the power into the switching relay only on in run and start? i am also going to jumper the oil pressure sensor connector as well, just to eliminate one possible problem from the circuit...if you can please tell me where to find the sensor?

 

because i already replaced the selector relay with a new one...but the fact that i saw power when i jumped the yellow to pink/black in the cutoff relay socket tells me the issue is in the cutoff circuit...which i believe points to either the cutoff relay being bad or that power isnt flowing through the pressure sensor.

 

Yellow to pink means nothing.
The spark is because of the voltage dropping resistor on one side.

Did you check the #18 fuse?

The oil pressure sensor and the pressure sender are at the back of the intake manifold below the EGR.

Why don't you just do as I said and resolve the problem?
You know there is power from the pink wire when cranking.
The issue is must be beyond that if you're getting no fuel at all.

 

i will...next thing imma do is bypass the pressure sensor because either way so that i can diagnose the system without having to crank and waste battery power.