Mech fuel pump question

[Redcap]

I had my fuel pump crap out today while hauling a load of gravel. Fortunately, I kept a spare old one in my barn, but I don't know how long it'll last. My question is this: if I tee an electric fuel pump into the line on a switch as a bypass around the mechanical to limp me home in case it happens again, will I need to install a check valve on the mech fuel pump output?

[knightfire83]

Technically, a mechanical pump already has 2 check valves inside the pump which will only flow one direction.

But,

The only bad thing of this would be if the outlet check valve hung open, and you had a ruptured diaphragm in the mechanical pump. Then the electric pump would fill the engine with gasoline.

Maybe the inlet check valve hung open on the mechanical one, with a bad diaphragm and then the electric pump would just suck air and no fuel.

Or perhaps both check valves hung open and you had no pressure at all when trying to use the electric. I bet the chances of any of these to be very low.

Then the question becomes, will the electric pump hold line pressure against the mechanical one, when the mech. pump is in use?

Yes you could isolate each pump if you were to add 4 check valves, 1 on every line from the mechanical and electric pump. Or more easily, permanently mount the electric and cap the ports. When your mechanical pump dies swap the lines and go....

Or you could use 2 valves such as our fuel tank selector on the line going to the tank and one on the line going to the carb.

Yet another possibility is that newer fuel injected vehicles with dual tanks have a pump in each tank....

It all depends on how both pumps are designed & again I just ran all the possibilities of what could possibly happen.

Why not just keep a spare mechanical pump in the truck, or buy a high quality replacement mechanical pump and forget about the fuel delivery problems.

For a simple question, I made it pretty complex 'eh?

[fordman]

if you wanted a check valve the good way to do it would be to get an electric tank switch from a dent side with front and rear tanks. flip the swithc in the cab and the other pump would come on and open up to pump fuel.

[Redcap]

if you wanted a check valve the good way to do it would be to get an electric tank switch from a dent side with front and rear tanks. flip the swithc in the cab and the other pump would come on and open up to pump fuel.

I like this idea. Guess I'll be hitting the boneyards next week for one.

[papabug71]

Be sure to watch the duty ratings on the electric pump. Some of them pull alot of amps. You might need to wire it up with a relay...

[Redcap]

Be sure to watch the duty ratings on the electric pump. Some of them pull alot of amps. You might need to wire it up with a relay...

I had planned on wiring in a relay for it.

[Banjo]

if the psi is that low, it's a pusher. keep it as close to the fuel tank as you reasonably can. There is a hold already in teh stock frame under the intank gas tank that you can bolt through and let the other end protrude lower to keep that end down (one end has to be lower, they're not designed to mount level, which looks good, but can let it run dry and heat up FAST and burns out). If you mount in engine bay, it'll work too hard and burn out.

[papabug71]

Be sure to watch the duty ratings on the electric pump. Some of them pull alot of amps. You might need to wire it up with a relay...

I had planned on wiring in a relay for it.

Good deal

I have been told its easier to push fuel than it is to pull it...

[70_F100]

I have been told its easier to push fuel than it is to pull it...

I don't know about that.

An FE pulls fuel through at a pretty good rate...

[70_F100]

I have been told its easier to push fuel than it is to pull it...

I don't know about that.

An FE pulls fuel through at a pretty good rate...

Not only that, but it pushes it right out the exhaust!!!

[70_F100]

Double post, sorry.

Something's going on with the forum tonite.