I think the 2004 still has a fuel rail test port on the passenger side of the fuel rail.
Harbor Freight has an adequate fuel pressure test gauge for $20 #62623.

The inertia switch is in the driver's side rear compartment.
You can probe the connector pins with a small paper clip to measure the volts.

 

I did check for codes and had the P0231 fuel pump secondary circuit low.


Here's how I tested for power output from the fuel pump relay. I connected the meter and drove until engine stalled.


When I lost power on my meter, the engine would die. I disassembled the central junction box like this, and seen the overheated fuel pump relay.

I think I bought the replacement relay R303 off Amazon. I also bought a solder iron kit from Radio Shack that contained a solder sucker. Heated solder from burnt relay pins and removed with sucker. Removed burnt relay. Installed and soldered new relay. All good now for 6 months. Time consuming, but up and running @ $30 for kit and relay.

This may not be your issue, but was for my 2004 Expedition. Hope this helps.

 

For what ever reason my fuse panel does not have the solder relays on it, they all are plug in type. Could it be the panel was replaced once before??????

Marv.

 

I think the 2004 Expedition fuse panel is the same setup as our 2003 Expedition.
There are some replaceable relays on the front of the panel.
The fuel pump relay and others are soldered to the back of the panel.

 

I think the fuel pump relay is one of the more heavily used relays in the vehicle and Ford's decision for placement was poor.
If I measured the pump resistance properly the pump draws 15A thru the 20A rated fuel pump relay.
On our 2003 I routed the output of the fuel pump relay to trigger a new 40A rated relay mounted under the console.
The original fuel pump relay now triggers the 40A relay and has only .2A going thru it's contacts so it should last a long time.
I added a voltmeter to monitor the alternator and hooked it to the fuel pump power source.
The fuel pump line tends to run a few 10ths lower than voltage at the battery probably because of the load from the fuel pump motor.

 

It's really not a good design. If I had that fuse box, I'd use heavy gauge wires and mount the relay externally so it would be easily replaceable in the future.

 

Agree, if I had the fuse box out I would try to make an extension harness, too.
The wire to the inertia switch is 14AWG and 12AWG wires aren't that much larger to work with.
I haven't seen what the back of the fuse box looks like so I'm not sure how the harness would exit the box.
My relay is working fine, I added the 2nd one to reduce the current thru the OEM relay as a preventative measure.

 

R&T, I'm not that good with electrical. Could you describe in more detail how you did this? I rather not have another relay problem. I am second owner with @ 120K miles now. Thanks.

 

Here's a diagram I used for the conversion on our 2002 6.8L Excur.
I used it to add to our 2003 5.4L Expy, very similar.
The thick lines are factory components.
The inertia switch is after the Test Switch connection point in the Expy.
On the Expy most of the components are mounted in the center console.
I ran a new high current line from the battery to a new post in the console.
The 20A On-On switch activates the new 40A relay in position #1 and restores the circuit to factory in position #2.
The 20A Test switch (On-Off) allows bypassing both relays for testing.
The switches are mounted just above the glove box right end out of sight.
Open the glove box to access the switches.
The switch position box on the drawing is taped to the back of the glove box.
The 40A relay is a standard auto style with arc suppression, which may not be necessary.
I got all the parts on ebay - relay,socket,switches,breakers,wire.

 

Thanks for that R&T!