Why do people install electric fuel pumps?

[Barry Wolk]

98% of people think that a hot engine compartment causes the most overused term, "vapor lock", when they don't care to learn why they have a problem. I guess that's normal. The anecdotal response is, "I went to an electric pump and the problem disappeared." Yes, it did, but all you did was throw good money away, and could cause your death, or great injury in a fire.

Engine compartment heat is just one element of vapor lock, better described as chaos inside a worn, or inoperative, fuel pump. Slow starting is a function of gas draining back to the tank by passing through a worn or inoperative check valve in the pump. Each Mark II has a combination vacuum/fuel pump that uses a common shaft to drive two membranes, one for the vacuum pump and one for the fuel system. A check valve's sole function is the make air or fuel travel in one direction only. By combining two, installed on the intake and output lines, each time the engine rotates one revolution it moves the membrane to draw in a dose of fuel into the membrane chamber through the spring-loaded check valve. When the stroke of the fuel pump changes direction the input check valve closes, leaving the only the output check valve as a place for the fuel to go. Once that stroke is done there's another dose ready to be sucked into the membrane chamber, but held back by the spring loaded check valve.

What happens in "vapor lock" is the pump loses the ability to pull, or push, fuel out of the gas tank causing chaos in the membrane itself. It's the inability of the pump to draw new fluid into the membrane chamber that causes the line to go dry. That's vapor lock. Yes, vaporized fuel doesn't help, but it's a check valve that's causing it. Vapor lock isn't a proper name, at all, but it caught on as a catch-all excuse for not finding the real problem. The problem is exasperated by tank venting problems that cause a vacuum in the tank making it much harder to draw in fresh fuel. Venting problems are sometime part of the poor fuel flow condition. I've seen blocked up vents, as they leaked when people topped off the filler neck.

The common response from people trying to help you give you the impression that changing to an electric fuel pump is the panacea for "vapor lock", but it's just an unnecessary, expensive and dangerous "improvement" when it's not really an improvement, at all. In fact, they can be deadly in an accident. Let's say your brakes fail and you slam into the rear end of an SUV or truck. You're knocked silly and don't give a thought to the running fuel pump until it keeps running through a ruptured hose or the vents in the carb. There are dozens of examples of this on the internet. That's not the way I want to die.

Modern cars use an electric fuel pump for a variety of reasons, most of of which are electronically injected fuels that requiring higher pressure. All of those cars have crash sensors that are designed to shut off the fuel and electricity in an impact. Some of these sensors are resettable, some are not. If you don't have that you really shouldn't leave the pump on while driving. What you can safely do is use a momentary contact switch, one that only makes contact when your finger is on a spring-loaded button, or handle, that will turn the pump on long enough to overcome the chaos in your pump's membrane, pushing liquid fuel through the pump, making it run again. However, this is just an example of throwing money at a problem when the solution is masking another problem.

What is actually the best thing to do is change the pump for a rebuilt, or rebuild what you have. Inside the mass-produced pumps I'm sure they never saw the need to rebuild many pumps as dealers only installed new ones. For that reason they took the cheap way out and pressed part of the soft zinc housing over the edge of the check valves to hold them firmly and evenly in place with a press ensuring that the seal does it's job. However, subsequent rebuilds have no spare zinc to peen over. If you've done it without a jig it's not very likely that the valves are sealed, and even a tiny gap will ruin pump performance, aka, "vapor lock".

Another very good reason to rebuild the pump is that the flexible membrane is the only barrier from keeping gasoline out of your crankcase oil supply. The tiniest leak can siphon a lot of gas into the oil. If you ever see a dipstick with no foam on it, but a higher than normal oil level that extra is gasoline, and that simply thins the oil. If you see foam that's from moisture or a coolant leak. It can be indicative of a blown head gasket, too. If you use an electric pump the pump makes things worse by delivering more pressure to the breeched membrane than a worn mechanical pump would have.

I'm not anti-electric fuel pump, at all. I'm simply cautioning that there are inherent dangers involved if not properly installed. The anecdotal evidence is that it's a properly working mechanical pump that will solve 99.9% of fuel deliver problems. While an electric pump solves 100% of the problems, it can also create some deadly ones. If you use a momentary contact switch you've successfully provided a fast way to start the car, and you can easily conquer "vapor-lock" while rolling. I did this while crossing Michigan at 45 mph in our '33 Continental Flyer. I used the button 4 times and the engine roared back to life in a second, startling us, but kept us on our way each time. The fuel pump was rebuild and solved the problem.

As a personal anecdote a momentary contact switch on the '42 Lincoln-Zephyr likely saved our lives as the pump was not on when a semi literally ran over the car, crushing the gas filler pipe in the rear fender. The semi ran up the trunk and tipped the rig and trailer, spilling tons of scrap steel and tying up the freeway for 4 hours. We were sent off into the weeds in a 90mph spin
that stopped when we went into a slide as I watched the trailer split open right in front of me. My wife passed out during the high speed spin, but I held on to the steering wheel with my foot on the brakes. We slid sideways another 100 feet, while I thought we might slide to a stop. No such luck. A tire was pried off the steel wheel and it caught in the dirt acting as a pivot point for a change in direction and a side over side spin for another 100 feet, in the air for 100 feet, leaving no sign in the grasses between there and the impact point. We flipped 5 times. I saw the sun through the windshield and counted. We landed upside-down, with the engine running. It stopped after we came to rest on the roof. My wife had bashed an escape route when her belted body smashed into the passenger door, opening it with her head and shoulder. I rolled over her, later learning that I had broken 4 of her ribs. I didn't know, but I had severed 2 of 3 hamstrings from my hip and my leg wasn't working. I pulled myself up as saw 15 foot flames coming from the rear of the car. I managed to pull her out of the car, and someone cam along and carried her to safety. Someone was pulling on my collar when the gas tank emptied and exploded, knocking rescuers to the ground. We were saved by people, as well as a simple push-button switch.

Please feel free to correct me if my facts are wrong. I'm alway willing to learn new things. This is what I was taught spending my wayward youth working weekends at my uncle Milt's Standard station on 8-mile and Meyers in Detroit.


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