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Discussion Starter · #1 ·
We replaced the inline fuel pump (and fuel filter) in my son's F350 pickup after a no-start start when the fuel pump stopped working (with the ignition ON). None of the Battery Junction Box fuses powering the Fuel Pump Relay 20A #19, IDM Relay 30A #27, and PCM #24 fuses are blown. With the IDM module disconnected, we've verified 12V is present at pin#14 on the IDM connector with the ignition key ON, so I assume the PCM and its IDM relay control signal (either 0-.25V, 4.6-5V, or 12V ??) from PCM pin #80 is working fine. (Using the attached 2002 F-Series Powerstroke Schematic, I assume the IDM relay only supplies 12V (no ground thru the relay) to the IDM module, which controls power to the glow plug relay and injectors as needed.

We're trying to determine: 1) Where the possible short in the PCM relay harness might be. And, 2) If the PCM is still good. I Plan to check all the wiring going into the the Battery Junction Box to the PCM Relay receptacle for possible shorts before probing the PCM pin #80 (IDM Relay control signal) Also, I can't find any reference as to what the IDM-EN control signal voltage from PCM should be.

Any suggestions about where to start, and what other things I should check is appreciated.


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I think I'm using the correct Battery Junction Box diagram, below.

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I removed the large relays and the PCM Diode from the fuse box, and they checked out fine. When I check the PCM relay sockets in the fuse box, I get the following voltage readings:

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Also, I
 

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Whoa, Back the truck up.!

Start with what happened. Did any fuses blow and which ones?
There's an inertia switch behind the passenger side kick panel which kills power to the fuel pump if tripped. It can be reset by reaching above the panel by the hinge pillar and pushing the button. If it clicks, it was tripped, and the fuel pump should start working.

Also, include what year you're working on, because changes were made in 02 models for wiring. Since you have a Battery Junction box, that tells me you have a '99-'01 truck, but not everyone knows that.
 

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Discussion Starter · #3 ·
Whoa, Back the truck up.!

Start with what happened. Did any fuses blow and which ones?
There's an inertia switch behind the passenger side kick panel which kills power to the fuel pump if tripped. It can be reset by reaching above the panel by the hinge pillar and pushing the button. If it clicks, it was tripped, and the fuel pump should start working.

Also, include what year you're working on, because changes were made in 02 models for wiring. Since you have a Battery Junction box, that tells me you have a '99-'01 truck, but not everyone knows that.
 

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Discussion Starter · #4 ·
Thanks Mr. Hansen !
This is a 1999 model, manufactured in July of 1999. The only blown fuse we found under the hood or under the dash was a 20A mini (#4 - Trailer reverse parking lamp), no others. Someone had put a 30A Maxi fuse in the fuse #19 (Fuel Pump Relay), which we replaced with a 20A when the new fuel pump was installed. We tested the Inertial Fuel Cutoff Switch (it was still in the "Down"/closed position unplugged. We are getting 12V to the cutoff switch Hot lead with the key On.

I failed to note that the Wait To Start lamp isn't coming on in the dashboard when the ignition key is placed in the ON position.

Yesterday, In addition to the fuel pump and filter, we also replaced the Glow Plug Relay (at the suggestion of a friend who owns a couple of these). Today, when we tested the new Glow Plug Relay for voltages from the battery/PCM control circuit, we got the following results:

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Also, upon disconnecting the PCM connector, my son found several wires that appear to have been chewed on, with one of through the insulation.
 

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Discussion Starter · #5 ·
While we're at it ( per the picture I previously posted of the Battery Junction Box in our truck) were we correct in replacing that Mini Relay we believe powers the Fuel Pump ?
 

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Discussion Starter · #6 ·
This all started with a no-start condition, after the fuel pump had failed. Also, when we replaced the filter along with the pump, the bowl was full of fuel. Which is why we suspect either a problem with the PCM itself (controlling the fuel pump, glow plugs, and communicating with the IDM ?) or something in the wiring harness.
 

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That mini relay you replaced was not the fuel pump relay. The FPR is located under the dash behind the radio along with the turn signal flasher relay and another relay.
But if you aren't getting 12V to the GPR from the PCM power relay (which also turns on the PCM), then I would suspect a problem with that circuit, either the relay or the wire from the Battery Junction box output of the PCM power relay to the splice that feeds the PCM, IPR, GPR, Intake Air Heater Relay, and the automatic transmission. There are actually two feeds from the PCM power relay to the PCM, and possibly if one isn't getting power, only part of the PCM is working.
You said you were getting 12 V Key-on at the inertial cutoff switch, so that means the FPR is good. But the fuel pump circuit is provided a ground via the PCM, so if that's not there, the fuel pump won't run.
I would check those chewed wires, which may be your whole problem.
 
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