fuel pump not coming on. trying to find fuel pump electrical circuit schematic to help troubleshoot as well as locate relays, modules, connectors,or whatever is in the circuit. would prefer not to drop the gas tank unless necessary. Any help in locating the components and/or troubleshooting would be much appreciated

 

Welcome to the site..

First thing, I'd check for power distribution 'at/through' the inertia switch. If present there, it quickly takes the guess work out of circuit protection, relays etc.
If missing, look forward of the inertia, it power is present on through the inertia, look aft of the inertia. If high mileage, could easily be the pump

 

Just got back to working on the truck. No fuel pressure. Started right up and ran briefly with starter fluid. Battery at 11.9v, inertia switch input at 10.4v and output at 10.25 v. Figure fuel pump needs replacement. Should I also be concerned about relay considering v. drop? Any other issues I should consider?
Thanks for the help

 

That voltage would bother me. I would recommend tracking down the cause on that.

The fuel pump relay (assuming it is the same on my 6.0L diesel and I believe it is) is integral to the Central Junction Box (fuse panel under the drivers side dash) - soldered in and not serviceable. Repairing it is not an easy fix (if it is your issue). I would get a wiring diagram and see what the voltage was going into the fuse box, and coming out of it.

If you do have an integral relay and it is your issue, there are a few companies that will do the circuit board repair:
CircuitBoardMedics
automotivecircuitsolutions

When I did mine, I just installed another (external) relay - bypassing the integral one.
Some people talk about converting the integral one to be just a helping relay (lower the amperage through it), but if there is a fault in the circuit soldering, this may not work.

 

Appreciate the response. The voltage does concern me. I have not yet been able to locate a source for a wiring diagram for this circuit specific to my truck. So far, I have been told the fuel pump relay is integral to the junction box, OR located under the dash behind the radio, OR located in a relay box in the engine compartment. Without a wiring diagram for the truck I guess I'm left with taking things apart and tracing wires. Any additional information would be very helpful and appreciated.

 

I wish I had a wiring diagram for your specific engine but I don't. Do you have the owners manual? If you do, it will have a diagram of fuses and relays. If you can not find a description of the fuel pump relay in that manual, then you can be assured that it is integral to your CJB (pretty sure it is, but not 100%).

You can jumper power straight to the inertia switch if you want to see if that makes a difference.

 

FPR is in the CJB,,

I can supply you with any schematics you'd need.

Check the KOEO voltage on fuse F2.40 ~20amp (CJB), should be close to batt voltage. If it is, then there may be an issue with the relay/connectors feeding out to the inertia.
As a test (test only), you could add in a 20amp protected 12v alternate source to the inertia switch, temporarily taking the power distribution control 'forward' of the inertia off the diagnostic table. Check for pump run, Y/N? If NO, the pump would be suspect or harness/connector possibilities on back to the pump. The FP only needs 12v at the pump module, ground for the pump mod/motor isn't dependent on the PCM. You can check for spec voltage at the tank connector as well with the test voltage applied prior to condemning the pump....

But, the PCM is in control of the FP relay grounding circuit and it's run time is limited unless a tach signal is detected.
At the relay, or the CJB connector, you should be able to verify the relays 12v ignition switched voltage, FP/load voltage from the fuse, as well as the PCM grounding function is present.
Seems PCM ground would be there or you wouldn't see voltage at the inertia. Same with switched voltage, the two would need to be present to close the relays contacts...

 

It would be helpful if I could access a wiring diagram that shows my trucks fuel pump circuit. Meanwhile, I am now getting battery voltage thru the inertia switch and am planning to drop the gas tank to verify the problem and if necessary replace the fuel pump.
Thanks

 

It seems easier to tie temporary power into the inertia switch to see if providing the proper voltage (and possibly the proper amperage) helps. Then (if it didn't help) drop the gas tank.

I just went through this with my 2006 (227k miles) diesel. The power into the inertia switch was a Dark Green wire with a Yellow stripe. Ford may have kept to the same wire color with the gas models. The difference is that my fuel pump is easy to get to.

I would also like to see a schematic if that isn't too much trouble.

 

I have yet to locate the relay or find any diagram or schematic for the circuit. However, I did disconnect the battery for a few hours and after reconnecting it the truck started right up and ran fine, although I did not drive it. After shutting it off, it would not restart. Guess the plan now is to drop the tank next week and check things out. Appreciate any suggestions