I know that I should run a bunch of tests and pull codes but let me give this a shot first. I was driving my 1987 E250 with 302 and auto transmission down the freeway at 60 MPH. Suddenly it started missing, the ammeter went from its normal mid position to 3/4 of the way to the charge side and engine died. Trying to restart was to no avail. I got towed home and checked for spark, which it had, so shot some starting fluid into the throttle body. I got a brief roar to life.
For many years my rear tank has been non functional and just run on the front with no problems.
I took a spare 12 volt battery, tapped into the pump's two wires and hot wired the high pressure fuel pump that's along the frame by driver's door. I included a 20 amp fuse that didn't blow. She fired right up and sounded good.
By the way I didn't find any blown fuses in the block down by the driver's left foot.
I inspected the fuel pump relay and the receptacle was partially melted. I replaced it and bought a new relay. I fully charged the battery and turned the key. She fired right up but the ammeter again went way over to the charge side.
I had just put on a rebuilt alternator before this happened even though the existing one worked just fine. To exclude the alternator from the problem I reinstalled the first time proven good one.

The new relay was getting quite warm and the ammeter wouldn't budge from its heavy duty charge position even though the big battery was freshly charged and topped off, so shut it down before cooking another one.
Any thoughts or comments would be greatly appreciated. Could the high pressure pump be drawing a huge amount of electricity and be the cause or should I start my search elsewhere ?
I disconnected the hot wire job to the fuel pump before the last start-up.
Thanks

 

Because the fuel pump relay is showing signs of an excessive current draw, you are on the right track.
What you need to do now is separate the pumps from power so one at a time can operate. If the tank pump OR wiring has a problem you should see and feel the relay get warm. If it does not, go after the hi press pump on the chassis and its wiring.
Whatever you do , replace the relay that was overloaded.
Let us know what you find, thanks.

 

Thanks for the input and quick reply. Having slightly more in the wallet than I have energy, I think I'll just start by replacing the high pressure pump since it's easy to get at and has never been changed since I got this thing back in 1993.
I won't have any wheels until later this afternoon so won't be able to get a new pump until later today. Pep Boys has it in stock for about $50. I for sure will keep you posted on the progress or lack thereof.
Thanks

 

Well, what to say ... I get different results no matter what I do. I have switched the tank selector switch back and forth after checking its integrity with ohm meter.
One time it will make the ammeter jump and the other side not. That is after years of it not making a difference in gas gauge volume readout or tank draw.
I just give up on the freeking diagnostics of it all and am ready to drop both tanks and replace the whole units in each and clean out the thing that switches them.
That will also be a new high pressure pump as well and filter.
It's no fun getting stranded and having to call and wait for AAA.
When I called last week I was told that I would not be allowed to ride with the tow-truck driver due to covid. I would have to call a friend to pick me up or get an Uber.!
So much for AAA after 27 years. Now I will be shopping for a new towing service.
Thanks again for the concern and help.

I'll post again in a week or so and let you know how it all sorted out.

 

Its nice to install all new stuff and can get pretty expensive.. Of course we "Hope" the new stuff was decent quality which can be quite a problem these days.
Your logic is worthy, however, you will never know which part was the problem if you replace them all at once. Circumstances do dictate what we do especially if we need the vehicle ,,,,,,,,,,,,,,,,,,,,,,,,,,, yesterday !

 

Keep in mind your vehicle has a separate voltage regulator to control charging. I believe it is mounted next to the radiator.

Older vehicles relied on ground supply through sheet metal on the vehicle. If there is an intermittent ground, the voltage, the regulator picks up could appear insufficient and so the regulator says, hey !,,, need more charging and that might be part of the problem.
Why was the alternator replaced in the first place?

 

Well, the alternator was a lifetime warranty from Pep Boys and the bearings had just a slight amount of side play and was making just a very little noise. I happened to have an old spare alternator and exchanged it for a new (rebuilt) alternator. I put that on and it was DOA. I removed it, took it back and got another one and installed it. It seamed fine and was driving down the road and that's when the ammeter went way over to the charge side and she died on me.
So, the first thing that popped into my mind was the alternator. It has an integral voltage regulator. When I got home, I once again changed alternators, putting the old tried and true one back on.
That didn't fix anything and that's when I found the melted pump relay harness which I changed as well as the relay. It has duel tanks and the rear hasn't worked in years. I would upon occasion switch between the two but every time I gassed up the rear was always still full even though the dash gauge never did register correctly.
It started and ran fine but with the switch on one side the ammeter would go over (charging) and stay over and the relay was getting warm so would switch it back. That would make it act as it should ... charging a little extra for a minute to replace the juice used from starting and then returning to the middle of the gauge. I had a friend turn the key on and off with the switch and I listened to both tanks. As expected, the front pump is working and the rear is dead.
I decided to replace the whole pump assembly in the rear tank but have to figure out how to get all that gas out of it so as to be able to drop it. I tried to siphon it but can't so am thinking about hooking the line for it up to the high pressure pump and see if that will work. I bought a new one of those at Pep Boys and put 12 volts to it last night and not a sound or spark from it. Just another DOA part from Pep Boys. I won't ever set foot in another one of their stores after I return this last item. BTW, I found the wires to the rear pump last night, put 12 volts to the red and black wires and started to get a little smoke.
So, I also need to disassemble the tank switching valve and try to rehab it or buy a new one. It sure as hell won't come from Pep Boys.

 

It is not our intent to poo poo any company's product , but when possible maybe save a fellow forum member some grief and problems.

Grant you there are a lot of good aftermarket products out there and unfortunately some not so good ones too, and you maybe happened to find one of the undesirable ones..
Those of us that have been burned , usually learn ,you may pay more for OEM,when available, but the quality is usually better.
There are companies that manufacture fuel pump complete tank units that are of good quality,you just need to do a little research , some are Airtex, Carter etc.
Just replacing the pump motor is really only half the job. There could be internal leaks in the pump module assy that you may not be aware of and just replacing the motor puts a malfunctioning module right back into the tank. You might give this some thought when you need to replace a fuel pump assy.

 

Sorry about the disparaging comments pertaining to a particular store. I didn't realize that was frowned upon.
I did buy the whole unit for the rear tank. I learned that lesson when I changed just the fuel pump motor in our 1992 Caddy.
The pump works fine but the fuel gauge only works half the time.
Thanks for the advice.