So is there no way to chase wiring? etc...



Im not going to go start throwing parts at this truck. Thats 200$ worth of parts without knowing if even either are the problem.

 

Crawl underneath the truck and meter the wires at the tank with the key on.

Looks like for the front tank, the fuel pump wire colors are Red/Orange.
Rear tank looks to be Brown-White/Orange wires.

Meter with key on to see if 12V is present. Be mindful, 12v will only be present for a moment or two after key is turned as PCM will shut off fuel pump with no PIP signal.

Inspect PCM by removing it and taking the cover off - if the capacitors have bulged/swollen/leaked all over the board chances are it is dead. Judging by the amount of codes, I'm leaning towards PCM.

 

Found this being the closest diagram i could get my hands on. Its for a 91 however all wiring colors are matching..



Went to fuel selector switch:

Red/Yellow - Power for 2 to 3 seconds then off until i try to crank

Front tank:
Red - Same thing as Red/Yellow
Dark Blue/Yellow - No power
(No sound of pump)


Rear tank that has supposable holes:
Brown/White - Same thing as the Red/Yellow when rear tank selected
Light Blue/Yellow - No Power
(Can hear the rear pump run)

 

Is the rear tank and front tank pumps interchangable?

 

Ford diagram for the fuel system on your 1992:

 

Be aware the fuel pump relay is energized for only 1-2 seconds when cycling the key from the Off to Run position. The computer is programmed to do this.

To keep the fuel pump relay energized jumper Pins 2 & 6 on the self test plug, then turn the key to the Run position. The relay will stay energized for troubleshooting purposes.

A photo from Subford:






The fuel pumps are interchangeable, but not the complete Fuel Delivery Modules (FDM).

 

The dark blue/yellow + light blue/yellow never gets any power at start of key on or while cranking motor.... But im getting power from the red/yellow which comes from the inertia.

So best way is to crawl up under the truck and find the yellow and red wire coming from the front tank. See if I get power from red to ground. If yes continue to testing power from orange to ground. If no power from orange to direct ground(frame rail)

Testing w/ Lighttester

Red/Yellow - Power for 2 to 3 seconds then off until i try to crank

Front tank:
Red - Same thing as Red/Yellow
Dark Blue/Yellow - No power
(No sound of pump)


Rear tank that has supposable holes:
Brown/White - Same thing as the Red/Yellow when rear tank selected
Light Blue/Yellow - No Power
(Can hear the rear pump run)

 

I assume what you mean when modules aren't interchangeable is meaning the entire fuel pump assembly. Yet you say the pumps are. Meaning I can take both assembly's out. Disassemble the pump(s) from the assembly and switch/reinstall.

Am I understanding that right?

 

Highly doubt you lost the ground to the front tank, unless when selected the fuel level gauge pegs past full.

The Dark Blue/Yellow and Yellow/Light Blue wires are for the fuel gauge circuit. Power comes from Fuse 17 and is hot in Start and Run positions. The same fuse supplies power to most (if not all) of the instrument cluster gauges. That will not prevent the fuel pump from running.

 

To the best of my knowledge, that I can recall, the fuel pump itself is not position based. The Fuel Delivery Module can be disassembled (FDM is position specific).

A photo to help understand what the complete FDM looks like disassembled:




A diagram of the completed assembly:


courtesy of Subford

 

So I should be getting power at the dark blue and light blue yellows when key is to run position? And the fuel gauge is at 1/2 full on front tank then drops to 0 when switched to back tank.

 

Yes, you should have power from the Fuse 17 through the instrument cluster to the fuel tank selector switch whenever the key is in the Start or Run positions. Based on your response "And the fuel gauge is at 1/2 full on front tank then drops to 0 when switched to back tank" means there is power.

 

So dropping both tanks > Pull assembly's out > See if pumps are interchangeable(Not assembly)

Not sure if i misread but does anyone have a definite answer either or not the pumps are interchangeable?

Just called autozone and its 200$ for an assembly or 110$ for pump.

 

and once i get them on the ground is there anyway for me to test them off the battery directly? or is that to much voltage or something?

Found my annoying ford fuel ling clip tool.. Bout to go freeze my ***. Still need to check the power to the pump at the tank location.

 

Update:
Electrical - Red powered , Orange No Power (Front tank) (Checked w/ rla205 #2 to #6 pin powering the pump continuously)
Disassembly - Cursin out the rusted tank strap bolts