Thread: Electric Fuel Pump Suction

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A friend has a Deuce coupe, built almost thirty years ago. It has an OEM style in-tank electric pump feeding a stock fuel injected SBF 302. The pump has started to fail, working fine on a cold start, and even for an hour or so of highway driving, but then it dies like the key is shut off. Allowed to cool off it does fine again, but for a lesser time to get hot, and it stops again. We've isolated it to the pump, but to change it means dropping the tank, and to drop the tank means disassembling the whole back end of the car - he did not build in ease of maintenance features on the tank mount.

The question - can he mount a good external electric pump low on the frame rail, one that has plenty of suction head, and pull through the OEM pump in the tank, at least for a while? Seems to me that I've seen it done before, but we don't want to mess up a good pump for no good reason. It's not a performance beast, just a stock Mustang engine, AOD cruiser.

it shouldn't be too difficult to raise the body at the rear without having to undo any wiring, steering, pedals,seats etc---------take out the 8 or 10 bolts holding the body on(maybe made some 3 or 4 inch long headless bolts that you can use to keep body/frame aligned) and pick up the back enough to get the tank out

Originally Posted by jerry clayton

it shouldn't be too difficult to raise the body at the rear without having to undo any wiring, steering, pedals,seats etc---------take out the 8 or 10 bolts holding the body on(maybe made some 3 or 4 inch long headless bolts that you can use to keep body/frame aligned) and pick up the back enough to get the tank out

Yeah, we can make it sound easy, but the fact is this is a car that was built long ago, has had tweaks & changes over the years, and getting the tank out is a CHORE that he does not want to tackle if he does not have to right now. Trunk is fully upholstered, without provision for pulling the body bolts, full fendered, bumpers, tank cover in back, etc, etc. Everything looks pristine, but after 30 years you get rusted bolts, corroded clips, and who knows what else. Not asking for help dropping the tank. The question is, "Can an external electric mounted low on the frame suck through the OEM pump?"

If the answer is "No", then the internal pump is going to be pulled, and replaced with an external pump so the problem is gone for the future.

Fairly easy way to tell.....get an electric pump but dont install it permanently and use it to pump from the tank into a 5 gal can. You can try different fuel levels, etc. Sit the pump close to the location that you will be mounting it at.
The stock pump will add some resistance in the line.... IF the armature on the in tank pump is free (and not binding), the new pump may work.....easy test.

Roger, to answer your question, yes, BUT the new external pump's lifespan will be greatly reduced having to pull fuel through the old in-tank pump (picture a big roadblock in the fuel supply). Even with a high quality pump, he will be replacing the external pump again. If your friend goes this route, the next question he needs to ask is, "where will I be when this pump quits?".

Mike

Originally Posted by Mike52

Roger, to answer your question, yes, BUT the new external pump's lifespan will be greatly reduced having to pull fuel through the old in-tank pump (picture a big roadblock in the fuel supply). Even with a high quality pump, he will be replacing the external pump again. If your friend goes this route, the next question he needs to ask is, "where will I be when this pump quits?".
Mike

I think you're right, Mike, and that's where we are right now. This is the car I tagged with to Des Moines, and we spent a lot of time by the roadside and working on it in the hotel lot instead of being at the show. He says that he's started it several times to shuffle cars around, and even took it out for a short trip and "it's running better than ever" - it has a new coil, new ignition module, all electrical checked & double checked in Des Moines - but he knows that it's not reliable for a long trip. It's always a question of when it's going to quit, and he'd probably be perpetuating that problem by not pulling that old pump.

It is what it is...Bite the bullet and change the pump...A lot of work but when done its over Been there done that.

Doing the Fuel Safe fuel cell in the jeep, we put two electric pumps in and plumbed them both out to the access plate. The power wires are connectorized so when one dies, the fuel line and the wiring can be quickly switched over.

Electric pumps where never designed to suck. They will to an extent but I can almost gaurantee it won't pull thru the other pump.

The Astro van in tank pumps do need replacement at about 100,000 miles. We found out the same thing about external pumps trying to pull fuel through a dead in tank pump. I does short life the external pump.

Originally Posted by HWORRELL

Electric pumps where never designed to suck. They will to an extent but I can almost gaurantee it won't pull thru the other pump.

Agree, and thanks for the input. Some pumps have better suction head than others, but they're all intended to be pushers.

Have you considered cutting and access hatch through the floor of the trunk? It could be done with minimal upholstery destruction, sure would make the next pump replacement easy. Lifting the body really seems like the hard way to go.

For information only, I am placing this picture to show that an electric fuel pump can work at the same level as the bottom the tank, it is the bed of my wife's 32 truck.

Pepi, that's a nice, clean installation in your wife's '32 and IIRC, it has a carb which only clouds the issue here, like comparing apples to oranges. Your Edelbrock pump is designed for the lower pressures a carb needs (probably approx. 5-6 psi) and is intended for external mounting, Roger's friend has an EFI engine with different requirements. Since I'm not a blue oval fan I don't know the 302 EFI specs but as an example my LS1 needs 58psi to run properly.

Mike

I had thought the higher fuel pressure of EFI could be a factor but was not sure, thanks for clarifying ...

I know a 255 LPH Walboro is what the Mustang guys use. IIRC Those Ford fuel injections run at 30 PSI stock. The 5.0's may run a bit higher... There might be a possibility of running a high GPH high pressure pump like what Aeromotive builds. They may provide enough suction to not stress the pump much, but that's an expensive venture if it fails... An in tank Walboro 255LPH is about $60 as a replacement for a stock Mustang pump.

The stock pumps are rotary vane pumps, so it may draw fuel just fine, but it also probably will burn the side pump up from working so hard... Walboro does make a 255 LPH pump for in line applications that will provide the correct pressure, with the cost around $100 IIRC.. I know while I was in the local Napa 1 day, there was a guy with a GM bread van in the parking lot with a dead fuel pump. His company couldn't get there for a while, so he bought an external pump that would work, and wired it to a switch directly to the battery, so he could finish his deliveries