For prior troubleshooting info/etc, please refer to this post...

https://www.ford-trucks.com/forums/1...agnostics.html

EDIT & UPDATE: Finally DID find a solution with this phantom problem that I couldn't pin down, so if you're at a loss then be sure to read on in this 2nd thread. My career involves troubleshooting electrical/mechanical issues but this thing had me chasing my tail for a while...

Alright, finally can give an update on this mysterious problem, and it gets even more mysterious. This is a flare side king cab 2 wheel drive with auto tranny if that matters.

I have power all the way to the two pin plug that the pump plugs into inside the tank. IE: Turn the key to ON but not going to the crank position. I get 12V for about 1 or 2 seconds like I should.

Fine, you'd think bad pump then right? Nope, thus far we've put a total of 3 new pumps in and none of them will run for that few second key ON priming sequence. We even switched to another brand with the 3rd thinking that the prior two were bad from the factory.

OK then, thought maybe I've got a ground that is dropping out under load. I think somebody said the pump's ground is located on the driver's side front fender.

Found what should be it. Sort'a just in front of the relay/fuse box, unless there is another? Took the bolt and ground wire off, cleaned them up via fine sandpaper, contact cleaner, and then a thin layer of dialectic grease to keep things good. Did the same with the very short main negative battery ground that goes from the battery to the front clip on the truck.

There is an aftermarket alarm ground wire also on this bolt, but this was put in before I bought the truck used and don't have the FOB for it. Shouldn't matter anyway since I'm getting 12V inside the tank at the fuel pump plug for a sec or two like I should with the initial KEY ON NO CRANK position.

Still no dice. Didn't have a second person handy to check for potential voltage difference between the ground wire and the frame of the truck for 1 or 2 secs when the key is turned on to prime the pump.

So unless there is another ground hidden somewhere that I'm missing, I'm stumped on this one. Fuel pump relay was replaced to be safe that it wasn't disengaging under load. PCM relay looks good but swapped it out for a sec to test that too. No luck.

Had also tracked the entire positive wire from the inertia switch to taking apart the harness under the seat inside and outside the truck. Looked fine. Had power on the pin for the fuel pump pin in that plug. Cleaned it up, put back together, and sealed things.

Maybe I've got a short in the negative or positive wire from the pump somewhere along the frame harness that is dropping out under load, or as said maybe I'm missing a ground strap or something? There is a ground strap from the filler neck to the frame, but are there any others related to grounding the fuel pump that I might have lost?

Has to be an under load electrical issue that doesn't show up when just reading voltage with a multi meter at the plug inside the tank, since the original pump had blown a fuse and the fuel pump relay looked like it had gotten hot. Under load something has to be dropping out.

Don't see any wiring between the outside plug on top of the tank and the plug for the pump inside that could disengage the circuit, and have power at the in-tank plug anyway for those few key on seconds, so it should run.

Shot in the dark and don't see how it could change the reality of the above, but how should the PAT light work? It blinks as normal with no key in. When I turn the key ON it comes on steady for a few seconds and then goes out, but when I crank the light comes on and stays on. Normal?

 

When working alone , get creative . Take your horn off . Wire it up with jumper wires to your fuel pump wiring . You can hear if you have proper power and ground . Or you can use an old sealed beam headlamp and see .

 

Too cold around here these past two weeks to get fancy with things. My helper was supposed to be around when I showed up but wasn't.

Simply put- How can I have 12V at the pos/neg plug for the fuel pump inside the tank for 2 secs at key ON as normal, but 3 pumps thus far aren't running? Has to be a load issue with the wiring. Just don't know what else to check with grounds and connectors.

 

You need to load test the wiring to the pump . A proper VDOM would be helpful . You say you have voltage . Supply your own Known good power AND ground . See what happens . If you run known good power AND ground jumpers to the pump , it should run .

 

Is your 2000 3.0L regular gas or a flex fuel?

If it's a FFV check fuse #11 in the box inside the cab.

 

You should run a direct 12 volt supply and ground to your pump and see if it runs continually to rule out the PATS or a wiring issue. Try a spare key to see verify if the transponder chip in your key is the issue. Here is a link on some info on the PATS (Ford Anti Theft):
Everything you wanted to know about PATS. - Ford Explorer and Ranger Forums "Serious Explorations"®

 

Well, it took over 2 weeks due to work/life and the extreme cold temps and snow, but gave it one last stab a few nights ago before admitting defeat and sending it to a garage.

Since my career involves troubleshooting mechanical/electrical issues I wasn't going to admit defeat until I gave it one last shot.

My multimeter was showing 12V at the fuel pump plug INSIDE the tank for a few seconds with KEY ON, after chasing all prior wiring to the tank since a few new fuel pumps still wouldn't run. Wanted to avoid dropping the tank again so I came at it from the source voltage side to rule out all other issues.

Well...when all other relays, fuses, and harness plugs still showed 12V feeding the tank, and when the tank was dropped once more and still showed 12V at the fuel pump plug, I knew it had to be either a phantom ground or the positive line dropping out under load.

Kept the pump plugged in and shot 12V to it via the output of the interia switch (already had checked that before for issues). Pump still wouldn't run. Shot voltage to it at the plug on top of the tank.

RAN!!! Was using a jumpered ground from one plug (input to the tank) to the other (output to the tank) so that eliminated a ground issue unless the two plugs were not ground to each other proper via those pins.

Then shot a ground test up the internal fuel pump ground of the tank to be sure....All good. OK then, the positive wire is dropping out under load somewhere between the intertia switch and the plug on top of the tank.

Since we had already taken apart/cleaned/inspected harness under the seat because on 2000 and 2001 Rangers they are know for water intrusion issues, knew I had a problem with the wiring harness between there and the pump.

Just to be safe, avoided jumping at the below floor wire for the fuel pump in this harness. Cut that wire at the output of the inertia switch and right at the top input plug of the tank to feed the positive side of the pump. Ran new wire from the interia switch OUTPUT (pink/stripped) through the floor directly to the wire input on the receiving plug going into the tank.

Turned the key to ON 3 times, turned it to CRANK, and prayed....After 2+ weeks she roared back to life! Man....Just goes to show despite me working in an electrical/mechanical field involving both, some phantom issues can be very hard to track down, especially if you don't have a good schematic to go by.

Was worried this truck being a Flex fuel might have been sensing the positive lead we cut out at inertia out and /input top of the tank ends to bypass things or still wouldn't run either due to an unknown positive routing through the flex sensor or it needing to sense the positive wire's energized state. Couldn't find a schematic for flex fuel and knew this stupid sensor branched off from the main under driver's floor harness that goes through the floor.

Just glad the old girl fired right up. This is my 3rd Ranger in a row and I put at or around half a million miles on them before selling off or sending to the scrap yard. She's only got 124,000 miles on her so I expect the beast to get me at or around 500,000 miles before she is sent off. All about preventative maintenance and also keeping the fluids fresh in all respects.

Thanks for all the help and hope this and prior thread will help others track down a p*sser of a phantom fuel pump electrical issue down the road.

PS- Soon as weather breaks going to pull every relay and fuse and give them a thin coat of dialectic grease. Didn't like what I saw when checking that. Small grime, and even tiny oxide build up can be a b*tch of issues. Always do coat a thin layer on any electrical plugs and O-rings to seal things when fixing stuff on a vehicle, but never gave a second thought to relays and fuses in the control centers. Way I see it it's cheap insurance against losing an electrical circuit down the road at the "brain" centers.

 

OK, good find, fix, feedback & to hear all now seems well & your on the road again!!!! EDIT: With the problem being wiring, you now have a spare fuel pump, if you didn't toss the old one out after replacing it.