Is my issue fuel pump or wiring?

My 2004 Expedition died on me while driving the other day. Found fuse 9 was blown. Was supposed to be a 15amp fuse but a 10amp was installed. Replaced fuse with a 15amp and truck started and drove just enough to get me to the top of the hill that i live on and died again. I was able to coast down the hill to near the house.

Replaced the fuse again to try to get around the cul-de-sac and back down the driveway, and the fuse blew right in the middle of the circle. Attempts to get a fuse up to 25amp to work long enough to get into the driveway were unsuccessful so I had to tow the vehicle up the hill to get enough momentum to get it into the driveway. During this time the fuses would pop pretty loudly as soon as the key was turned on.

Truck sat for awhile, replaced the fuse with a circuit breaker in a fuse buddy and it started right up. Sat and ran in the backyard for about 20 minutes without a hiccup. Current draw about 4.5amp.

Attempted to test drive the truck and it made it about 200 feet up the hill and died again. Was able to coast backward into the driveway. Reset the circuit breaker and the truck again ran fine and was able to get it back into the back yard. Now is back to running fine for extended periods of time at about 4.5amp draw with no issues.

Is it possible the fuel pump is heating up and dead shorting? I replaced the pump about 2 years ago with I believe a Bosch and never had an issue after. It seems more likely to me that something is shorting out in the wiring harness, which I am going to attempt to check today. If anyone has any experience with the harness shorting out I would appreciate some possible places to check. My back doesn't let me lay under the truck for long periods of time anymore.

Jeff

Adding: didn't notice any extreme bumps or jolts when the fuse popped. Was just driving along a pretty smooth road and it died like the key turned off.

Pretty sure that harness goes through into the body in front of the tank and behind the transfer case. It heads forward then crosses under the seats then forward under the right front sill plate. If the harness looks good to the body grommet, look under the passenger front door sill for water intrusion. Charm.li will give you wiring details with factory drawings.

Thanks, that's where I got my diagrams. I'm out here crawling around under it now, it's been sitting here running fine for about an hour.

It does sound more like an intermittent short circuit than a bad fuel pump. I would be tracing the wiring from the pump back to the fuse and see if the wiring has rubbed against the chassis anywhere causing a short circuit to occur occasionally. Intermittent faults are the hardest to find.

Wiring harness in the driver's side rear sill is sitting in some water but I don't see a 14g dark green/yellow wire. Passenger side is still factory wrapped and looks dry. Nothing obvious under the truck yet but it's hard for me to get in there. I guess I'll have to tear more apart on the next good weather day. Or maybe just do a new wire overlay from the fuse box back lol.

I would bet the dark green wire runs back to the inertia switch and is a different color from there back to the BCM.

It's dark green and yellow from the fuse box to the inertia switch and then I think pink and something to the pump.

Problem is I can't get it to fault again to even determine if it's fuse to switch or switch to pump. It sat and ran for about 2 hours today without a hiccup. Even drove it up the hill and back a couple times.

Mine did not blow the fuse, but when the fuel pump relay failed it acted almost identical to your symptoms. Let it cool down and it would run for a bit. There was nothing visible on the relay. You can only see the top when it's in the central junction box(CJB). Mine also smelled burnt. I pulled the CJB and it was clearly obvious that the relay was done as a corner of it had melted quite a bit. I did not think to check the temperature of the relay back then, but if you have an IR temp gun it would be easy to check.

If you happen to decide the Bosch pump is shorting out don't forget they have a lifetime warranty.

Thanks for the info. I thought about the relay and the load side is after fuse 9, but I wouldn't think it would be able to short to ground without some pretty major damage to the relay.

Back at it today but the truck started up and ran fine on a short test drive. Even beat it a little on some rough road. Worried that if I can't get it to short long enough to test I may never be able to trust it enough to drive it again lol.

I would put a high probability on the fuel relay, which is notorious for intermittent, progressively worse failures. There are lots of postings and ways to jumper around it for testing. It requires removal of the main fuse box on the passenger side to replace it with the newer, higher amperage relays. It is soldered onto the back of the circuit board, and again lots of videos on how to replace it, which I have done with great success. Good luck.

It is almost sure to be a problem with a wire shorting against the body or frame due the the intermittent nature of the fault, especially when it will blow a fuse with the truck not moving and then stop. If there has been any work done recently, I would start looking in that area since a wire harness could have been moved (or just loosened so it could now move). If that doesn't help then have someone wiggle the wiring harness gently while you keep and eye on the fuse (or do like I do and put a buzzer connected at the fuel pump, when the buzzer stops the fuse has blown).
You will be able to rely on the truck again ONLY after you have verified the cause of the short.
BTW, an overheated connector is a sign of either too much current draw or a loose ground connection there at the connector, make sure to check the tightness of the female side of the connector, the heat may have caused the metal to relax and no longer give a good tight fit.
The fact that it can run and drive means that all is not lost, the problem is just hiding.

I added an external relay to my 04, there is a new post in the 2nd gen section.