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Dual Fuel Pump Nightmare

Hi my name is Brian McGloin and I live in Missoula Montana. My father recently gave me his 1986 Lariat F150 Ford Truck. It is electronic fuel injected, this is where the problem is. My father has explained to me that this truck has two fuel pumps, one on the rail and also one in the tank. He has explained to me that this has been a nightmare to him and that he has replaced both pumps a multitude of times. I have spoken with a local mechanic who educated me that I could either install a carbureted manifold, which I understand will be very costly or replace both pumps which my father has already done multiple times. I do not have the resources to install a carbureted manifold, if in fact it is as costly as explained to me. Therefore it seems to me my only option is to spend the money to upgrade both pumps to fix this problem. I really want to take good care of this truck because it was a gift from my father. If you have any other advice or options that would work I would so grately appreciate your input. Thank you!

You’ll have to consider the ways the fuel pumps can be failing and eliminate them.

  1. the pumps are junk to begin with. Maybe you can figure this out and make sure you buy a better quality pump to begin with.

  2. The pumps are picking up debris in the tank(s) and causing them to fail prematurely. Check the tank(s) and filter socks on the pump inlets.

  3. The pumps have been habitually starved of fuel. Pumps need fuel for lubrication and cooling. If someone habitually runs low on fuel, it can lead to premature failure.

  4. The power supply to the pumps is marginal. Poor connections, undersized wire etc can starve the pumps for current and cause them to run hot. Check the terminations for corrosion or broken wires, the harness for correct wiring and no splices and the pump termination at the bulkhead to the tank. The fuel pump relay might be something to change as extra insurance. After all these years, the contacts may be pitted or otherwise compromised and causing loss of current capability.

Some thoughts for your consideration…

What exactly is happening to the pumps? Have you disected each dead pump to determine the mode of failure? I have seen lift pumps for dual tank arrangements. Is this the case with your truck?

My information indicates this truck came with a carbutator. Is this the case? Has the engine been upgraded to fuel injection? What is going on here?

I agree with @TwinTurbo and @Researcher. You need to understand why the pumps keep failing before giving up and putting on a carburetor. Ask your father for some additional history on the pumps. Did they get replaced at the Ford dealer or an independent? What was the symptom for replacement? Which pump failed first? You didn’t say if you had dual tanks or just one. Does he run it dry? Buy the cheapest gas? Any additional info would help us understand the source of the problem.

Just a note of caution on using the internet. Don’t use your real name and location for security. Who knows who lurks out there? You can go to your comment and hit the edit icon and take your name out.

We had a 88 f150, 302. Had dual fuel tanks. Are u referring to that? Never had any issues with fuel system.

I’ve heard that one before.

Unless your father installed genuine FoMoCo fuel pumps, I can guarantee that the fuel pumps won’t last very long. I went through this with my own F150 and with other Ford vehicles of that era.

For some reason aftermarket fuel pumps and spark plug wires wouldn’t last long on Ford’s of that vintage. They had to be FoMoCo parts.


Concur w/ @Tester, first thing is to only use OEM pumps meeting Ford’s specs going forward. I’d also very carefully inspect the wiring involved in powering up the pump circuits, especially the connectors carrying the pump current. These pumps use considerable current and if the connector corrodes even a wee-bit, the connector will heat up, making the connection even worse, which can result in a low voltage to the pump which can damage it. If there’s any doubt, just replace the connector(s) with a new one. Same thing can happen with the pump relay(s). At the very least, after installing new OEM pumps, monitor the voltage at the pin on the pump(s), between that pin and the case of the pump, make sure it is close to battery voltage when the pump is running.

Edit: One caveate, on some fuel systems the pump voltage can vary from the battery voltage by design. To speed or slow up the pump for example. The factory service manual should be able to tell you if it applies to your vehicle.

There’s a number of reasons why the pumps may not operate and it’s unclear as to whether these pumps have actually failed or were replaced on an assumption that they were bad.

That might be sorted out if you were to provide some details on how any pump diagnosis was done.

If this truck has a small block V-8 then a conversion to a carburetor is not that difficult or expensive to do but my opinion is that you should stick with the fuel injection and even the cursed TFI module.

If given the opportunity of moving forward or backward, forward is usually the better choice. Like OK above says, I wouldn’t go back to the carb. Small block Ford engines like yours probably have several campatible aftermarket intake manifolds you could install, with fancier injector modules available to match. If you want to change something, me, I’d change in that direction rather than going back to the carb.

I expect the fuel pump problem will turn out to be something simple so you probably don’t have to change anything other than the fuel pumps.

The only other thing I can think of is that with two fuel pumps, I could see a situation where they might fight each other if not properly matched. I wonder if the service manual has a procedure to test for this?

2 fuel pump set ups are fairly common. One fuel pump is designed to move a high volume of fuel and the other pump is designed to make sure the fuel gets delivered at the proper high pressure. When one pump fails it tends to overload the 2nd pump and both fail.

Since the pumps can be pricey a lot of garages just replace the “bad” pump and leave the other one alone. This means you get a new pump and a questionable pump. If the questionable pump goes bad, it can overload the new pump, and so forth. Unless you change both pumps at the same time you end up with a questionable pump all the time. You need to talk to dad and find out more details of the pump replacement. If you learn that only one pump was changed at a time that can be important.

If the truck is running at the moment I’d do nothing for now. When you have a fuel pump failure, replace both pumps and I’d second using a genuine Ford part. All the other tips are on target too. So, you should look at electrical connections, wiring (look for splices or damage), voltage delivered to the pumps, and keep the gas tank above 1/4 full to help the fuel pumps last longer.

A good fuel pump(s) should last 5 years. After that a pump can fail but most last 10 years. After 10 years you can kind of figure a pump will go bad on you at some point. Dirt in the tank, a dirty and restricted pick up screen, and a clogged dirty fuel filter can speed up a pumps demise. The next time a pump goes bad you should have the gas tank removed, checked for dirt and rust, and if it still sound steam cleaned before you put it back in the truck.

Since this truck is now just short of 30 years old you’d have to expect a few fuel pump replacements over all those years. There could be a bunch of gunk in the tank after all those years. Wiring damage; due to rodents, or worn insulation due to vibration, or a DIY splice job to get power for some accessory at the rear of the truck are all factors to rule out in such an old truck. For now I’d put off a manifold conversion and focus on figuring out the fuel pump issue(s).

It may not be the pumps. A friend has this same truck. He went thru new pumps thinking it was a bad pump. Turns out there is a line in the tank that had split in it. Take the tank out and check the lines out. This line is part of the tank. New tank and it runs fine.

Awesome! Thank you for your input!

thank you very much

appreciate the help