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Fuel pump works and doesnt work

Hi Guys, I have a 2005 Explorer.
The fuel pump died so I replaced it with an after market,
Everything fitted fine, car started, used it, came home and next day no start.
Thought pump must be dead, pulled the tank again, tested new pump operation by powering up. Worked fine getting power from car, so put it all back together again and it worked.
Same thing, this time same trip, drove for 30 mins parked for an hour got back in drove to get fuel, and drove home, stopping the car each time, 2 hours later moved the car to wash it, then 2 hours later went to put it away, no start. I unpluged the pump and wired it up to run while in the tank and could not get fuel to flow with the rail switch out.
Can’t believe it, got mobile mechanic to run a deep scan, comes up with all these faults, right tow truck to workshop.
Towie hops in and starts it right up. Grrr.
Work shop has it for a week cant fault it.
Go to pick up the car, starts and runs out the fuel in the rails and dies, mechanic can’t believe it.
I am getting a feeling the pump is randomly running backwards.

Does anyone know if this is possible.
I need the car for family holiday and I dont want to get stranded.
Any feed back on thoughts or possibilities would be great.

I suggest you use a rental…better be safe than sorry!

If you are getting power to the fuel pump but no fuel coming out of the pump, then I would say that is a bad fuel pump. Is that what you are saying?

Or are you saying that when you disconnect it and then reconnect the fuel pump wire harness it starts working again?

Id suggest next time it doesn’t run, swap the fuel pump relay our with another and see if that helps. And if Family vacation is soon- use a rental.

I doubt the pump is running backwards. My gut feeling is that there is a problem with the fuel pump relay control circuit. The mechanic really needs to eyeball a factory schematic. Some Fords use an Inertia Switch usually located inside the rear of the vehicle. Those have been wired several different ways; one direct to the pump and the other method is to have the relay trigger circuit in it. Just a possibility if your car has one of these. Inertia switches seldom go bad though; especially if they have the second wiring method.

It’s near Xmas so I would say leave the car with the mechanic and rent a vehicle for the time being. No sense in ruining a holiday over a flaky electrical system. And I doubt the first pump was bad.

I was considering a rental.

The relays was one of the first things I tried, although i was aware of the relay situation at the back, and I didn’t check the wiring diagram before to see if thats the issue that could be related.

The perplexing thing is without disconnecting and reconnecting the harness or even moving the car it will work and not work.

Even one of the times it wasn’t working and the In despiration I disconnected thw battery for a few mins and when I reconnected it worked. Leading me to think it could be the ECU at the very least an electrical problem. Is it possible the ECU is reversing the polarity?

I’m hoping to hear by the end of the day from the mechanic if he finds something

Polarity reversal is possible I guess but I just can’t buy into that theory myself. The pump would still run; just backwards since it’s a DC kotor.

I rummaged through my books and do not have a schematic for your vehicle. Generally speaking, the relay trigger circuit has power to it on one side and the other side grounds through the PCM AND the Variable Load Control Module if it is equipped with a VLCM.

When the key is turned (engine not cranking) a ground is made through the PCM for the pump relay trigger circuit. After a couple of seconds the ground goes away unless the engine is cranked over.
If the engine is cranked over the ground remains and the pump is energized. As you can see there are a number of intermittent possibilities here.

For test purposes only, a jumper an be made at the pump relay terminals for the pump main power circuit. This will energize the pump instantly and you should hear it run. If the car runs fine with no issues then you know it’s back to a crank sensor, possible PCM issue, or even a VLCM is so equipped. The car should not be left like this as the pump will never shut off.

The ground through the PCM/VLCM etc could be checked at the pump relay terminals with a test light or Ohmmeter. Key on, engine not cranking should show continuity for a few seconds. It that continuity disappears while cranking the problem is likely the ground circuit in the PCM. I have seen this a few times including once on a so-called “Remanufactured” PCM that gave up almost immediately in use. Hope some of that helps.

Thanks for getting back to me.
Those thing all work fine for me.

You can here the pump run for a few seconds then shut off then when cranking it runs again. Even tried the power to the relay socket, which runs the pump but no fuel flow.

I even asked Ford if I could speak to an experianced tech, but because they don’t make money giving advice over the phone, they are unavailable to speak to me, and the said I could book it in with them, and the the same thing will happen, it wont present the issue for them and 3 hours labour for nothing $$$$ thanks.

You might be right about the PCM though, thats why its at the shop, I’m at a lost with my tools and experiance, I do have the wireing diagram and will investigate further.

Again thanks for your help.

What are the fault codes? You sure your fuel filter is not clogged up? Sometimes the problems are the ones that are easiest to fix.

Hi, new filter, and just the basics, no rail pressure.
I cant even get fuel to the line before the filter when it happens.

I’ll keep you updated.

Try to find a shop that has a scan tool that can turn the pump on and off by scan-tool command. They can monitor the fuel pressure (engine not running() while they turn the pump on and off. If the fuel pressure doesn’t follow the pump on/off, then they’ll have a big clue to work with. If the shop can confirm the fuel pump is getting it’s full voltage allotment but doesn’t turn on and run and pressurized the fuel rail, pretty good chance the replacement pump is faulty. Faulty out of the box aftermarket parts are not an unusual thing reported here. Unlikely to be running backward. Usually this problem – if the pump is faulty – is a poor electrical connection between the armature and the brushes. Or the pump’s mechanicals are just out of whack.

That was my thinking as well

I can’t remember all my fuel pump problems. For several years almost a year to the day, the pumps would go out. Sometimes the tow would jiggle it enough to start again. One time I got two blocks away from the shop after a new pump and it stalled. Walked to the store to call a tow and back to the car and it started again. Shop once said they had three Delco pumps in a row that were bad. Also had a bad contact at the plug. I’d never use an after-market but if I ever had a pump problem again, I’d trade cars.

Just for the record though it is recommended to change the wire harness and the relay at the same time as the pump because of the excess draw. I even went so far though of running a new wire from the pump to the computer just in case. Both cars are washing machines now. The third one with a pump problem I didn’t bother with and just called the junk yard to come get it.

With the pump running in both positions I’d say the PCM is good. Something for consideration might be this.
Most pumps have a check ball and spring to maintain residual fuel pressure while at rest.

Somewhere back in the early 2000s I think it was Ford started doing away with that setup and went to a fuel pressure sensor which is a separate item. I wonder if the FPS could be messed up and blocking the fuel flow to the fuel rail?

There are a few diagnostic codes that can apply to a pressure sensor as it is an electronic part. I think they’re about 120 bucks or so at AutoZone. Just something for consideration anyway.

Hey guys,
Shop managed to get it to play up out of the tank.

Turs out the presure regulator was sticking open. And dumping all the fuel back into the tank.

So the result is dodgie after market Chinese made brand knock off.

New brand name pump working perfectly.

Thanks for the input.



Hey, just giving an update:
Got the car home on friday arvo, mechanic said It was right to go away with. $938

Went to go to the shops the next day, you guessed it, wouldn’t start.

And of course he’s shut up shop for the Christmas new year period.

So had to take a different car away.

No a happy customer!

Away until the 6th, so I’ll worry about it when we get back.

I got the problem sorted after the 3rd replacement pump failed.
The issue was none of them were Genuine Ford pump assembly’s,
The problem stemmed from the size of the releaf pipe.
The output pipe on my old genuine pump is 12mm ID and all the after market ones including Bosch had a 6mm pipe. Increasing the back pressure 3 fold.

I should mention this problem may not have presented it’s self as normal pump, however as my car also runs on injected LGP, this stopped the fuel dead in it’s tracks and forced 100% of the constant running pump to TRY to dump all of the fuel through this tiny 6mm pipe.
Which inturn caused the valve to cease shut stopping all fuel from getting though.

So when running on LPG, always use a genuine fuel sender!

Happy Motoring!