I'm finally getting to my 1980 F150, 351M, 2 wd, at. It sat for 5 years and when I tried to start the truck . It would not start. I narrowed it down to no fuel. I searched for the fuel pump and found no mechanical pump but found a electric pump on the frame rail on the drivers side. I also found a electric pump in the engine bay mounted or fastened to the AC compressor mount braket. I installed a new electric pump on the frame. Truck starts and runs. But I need to know the correct arrangement. I think I should only have one electric pump but at what location. There is no provision for a mechanical pump that I can see.

Any insight would be very helpful and appreciated

 

That's really strange you had two electric pumps. I suspect the original mechanical pump failed, and it was replaced with an electric pump. After when the first electric pump failed, somebody cobbled in a second one without even removing the first.

If you want to stay with an electric pump, locate it as close to the tank as possible. If you've got dual tanks, put it just downstream (forward) of the selector valve so one pump can draw from whichever tank is selected. Fuel pumps are good at pushing fuel, but not so much as pulling fuel. If you pull a long distance, the fuel tends to turn to vapor. That's why you want the pump close to the supply, so it's pushing liquid fuel under pressure. Keeps it away from engine heat, too. Heat makes it easier for liquid fuel to turn to vapor. I've NO idea why some mouth-breather mounted an electric pump on the engine. That is literally the worst of both worlds, a hot location that has a long path to draw fuel. Alex, I'll take Vapor Lock for $800, please!

If you do keep the electric arrangement, make sure you include an automatic shut-off, in case of an accident or fuel leak. You cannot rely on your ability to turn off the ignition in an emergency. Details at this link about how I switched to an electric pump on my '84 351W:

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


This video shows the location of the mechanical pump on a 351M, just forward of the oil filter:



If the mechanical pump has been removed, you should see a block-off plate covering the hole on the side of the timing cover:



Not sure about the 351M, but on other engines you can install a later model or aftermarket timing cover intended for an electric pump, with no provisions for a mechanical pump. So if you can't find anywhere a pump would have been, the timing cover may not be original.

 

Some gas rigs had the fuel pump in the tank. Not sure if those are EFI or carbed engines. Regardless that has to be the stupidest location for a fuel pump. I'm sure they made sure that the pumps in the tank would outlast the warranty period.

 

Au contraire, an in-tank pump typically lasts a long time. Maybe the in-tank pumps on trucks of our era get a bad rap simply because they are coming up on 40 years old. And the installation is something of a first-generation afterthought.

But nearly all modern fuel-injected vehicles have the pump(s) inside the tank. The location is well protected. Cooling is not an issue, with the pump submerged. Same with cavitation, never an issue unless the tank is empty empty empty. On my car, the original 20 year old pump is still going strong. Unlike our trucks, replacement is easy with a convenient access port on top of the tank, once you remove the back seat's bottom cushion.

 

Most were EFI but I believe the later 80's larger motor trucks also got the pump in tank like the 460 motors.

The in tank pump is not at all stupid from a vapor lock stand point.
Anything under a vacuum (fuel pump sucking from tank) has a lower boiling point.
When you pull a vacuum on the AC system you are boiling any moisture in the system before you charge it.
Same happens to the fuel in the lines from tank to motor.

Anything under pressure (fuel pump in tank) has a higher boiling point.
With today's fuel blend it vaporizes(boils) at a lower point and why the pumps are mounted in the tank and run at 50+ psi.
BTW you know the radiator cap is in place to up the boiling point of the coolant?
IIRC for every 1 PSI raises the boiling 2*f so a 10 psi cap should not boil till 232*f and most new systems run with a higher cap psi so the motors run hotter to burn all the fuel to meet smog.
Dave ----

 

Do you realize you inadvertently agreed with me? Did we just become best friends?



Do you want to do karate in the garage?

 

Yah, I'm aware of the benefits of having an in tank pump. And a handy access hatch is a novel idea. But the next time you have to drop a tank to replace your pump...try to hold your tongue.

The cooling advantage of in tank versus pump near the tank is minimal. If you're moving cold fuel through the pump and suction head is low the additional "warming" isn't much. Then the fuel goes to the pressure side of the pump right away.

Heck attach the pump to the tank if you need a heat sink. But whatever you do make replacement reasonably simple.

I've put 100's of thousands of miles on mechanical fuel pumps. Easy to change. But the fuel I used was always 5 percent ethanol maximum.

We should stop making ethanol for fuel. But that's a subject for another post.

See ya in the garage...

 

My thoughts exactly especially with all the doom and gloom right now about food shortages. Why we wasting food to make substandard fuel? but yes another topic for another subforum.

 

All EFI trucks had in tank pumps and the early EFI models had a frame mounted pump along with the in tank pump.

When the 460 trucks came out in 1983 or 84, they had a hot fuel handling option and those had in tank pumps with a carb. I believe some 351w f250-up trucks may have had this system also, but I have never seen one. All other trucks had mechanical fuel pumps.

 

I'm only buying non ethanol fuel now. Sometimes the best way to cast your vote is at the gas pump.