Thread: Electric Fuel Pump - 101

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There has been a rash of posts concerning electric fuel pumps of late. We’ve discussed the “pros” and “cons” of both electric and stock mechanical units and while I’m a big fan of the stock units (especially on GM engines) I realize that from time-to-time, there are very valid reasons for installing an aftermarket electric unit – typically for space or clearance reasons.

One thing we have not talked a lot about (Jerry implied cost and a few key items as I recall) is how to correctly install an electric fuel pump. I’m a firm believer in braided stainless steel hose (3/8” minimum) and correct AN fittings – not barbed fitting with worm clamps – as I want to sleep well knowing the fuel delivery system will not be a safety issue on a car that I have worked on.

The electrical piece is the one most often overlooked. The worst (and very dangerous) way to install an electric fuel pump is to directly wire the pump to a switched source. Not only do most people use a wire that is too small and risk pump failure from drawing too much current, a direct link has no safety measures.

I like to use an “Electric Fuel Pump Safety Controller” device made by Revolution Electronics out of Cypress, California. This device provides a three second “on” time for fuel priming and thereafter will shut down if the engine is not running. They accomplish this by way of the tachometer lead from the distributor rather than an oil pressure sensor like many others do. This way you get a full three seconds of power to the fuel pump circuit without having to wait for the starter to crank up the oil pressure to 7PSI (most sensors) and more importantly, if the engine does not start you’re not supplying fuel under pressure to the carburetor. This is really important to hot rodders as we tend to let our cars sit for prolonged periods of time and while well intended, sometime without fuel preservative and the gas in the float bowl gets nasty and the needle sticks open. Ever seen gas pour out the carburetor when the float is stuck? I have and it scares me to death.

In addition to the Revolution component, I believe in relays for high current devices, like an electric fuel pump. I’ve drawn a little schematic of how this goes together (below). Key to remember is keep the Safety Controller and relay dry. On my 63 Nova, the battery is in the trunk so the relay is located there to minimize the #10 wire. The Safety Controller is under the dash, close to a switched source.

Hope someone finds this beneficial.

Regards,
Glenn

Nice write up and diagram Glenn.

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Very nicely done Glenn.
I asked Brent a long time ago to let us have a Technical Library where things like your diagram could be archived. I never heard anything of it, so I said nothing else. But it will be a shame for some of these tech articles to get away and not be accessible to the general public simply because they have no title to search with to find the post or thread.

I agree, nice diagram. One question, what size is the circuit breaker? To require 10 gauge wire the pump would have to draw in the neighborhood of 50 amps and if that is the case that would be one hot pump.

I am doing a project now that the owner wants one of those 'safety circuits' for the fuel pump. I am opposed to it because it just adds to the complexity of the wireing and provides no substantive protection unless it is dangerous to begin with.
For people that wire the fuel pump to the ignition switch then that safety device could have merit. The safest way is to have a dedicated toggle switch wired thru a relay to feed the pump. You don't even turn the pump 'on' until after the engine is fired and running. The driver has control of the fuel pump, his judgement is priority.
The advertised feature about shutting fuel off below 7psi oil pressure, an idiot light will serve you much better. In the event that you loose oil pressure and the fuel pump turns itself 'off' the carb has enough fuel to travel a considerable distance - the only protection that you have added is for the fuel pump itself. An 'idiot' light will get your attention so's you can get off the throttle and the highway.
When doing electrical, the simplist is always the best. I have done tons of wireing from model 'a' to hightech gorgonzo automatia systems and there is one thing i will pass on: when wireing the complexity goes geometrically. In this case, a simple switch/relay is being replaced with an automatic system taht the owner will want an override switch so's he can turn the pump on manually, right?, so the complexity went from twice to 4times.

I have always used a oil presure switch to cut off the fuel pump (with a relay). A manual switch won't shut itself off if you get into an accident and can't turn off the switch.

Originally Posted by ojh

I am doing a project now that the owner wants one of those 'safety circuits' for the fuel pump. I am opposed to it because it just adds to the complexity of the wireing and provides no substantive protection unless it is dangerous to begin with.
For people that wire the fuel pump to the ignition switch then that safety device could have merit. The safest way is to have a dedicated toggle switch wired thru a relay to feed the pump. You don't even turn the pump 'on' until after the engine is fired and running. The driver has control of the fuel pump, his judgement is priority.
The advertised feature about shutting fuel off below 7psi oilpressure, an idiot light will serve you much better. In the event that you loose oil pressure and the fuel pump turns itself 'off' the carb has enough fuel to travel a considerable distance - the only protection that you have added is for the fuel pump itself. An 'idiot' light will get your attention so's you can get off the throttle and the highway.
When doing electrical, the simplist is always the best. I have done tons of wireing from model 'a' to hightech gorgonzo automatia systems and there is one thing i will pass on: when wireing the complexity goes geometrically. In this case, a simple switch/relay is being replaced with an automatic system taht the owner will want an override switch so's he can turn the pump on manually, right?, so the complexity went from twice to 4times.

Problem is it should be wired thru the oil switch,not to save the engine if it looses oil pressure,but to save your butt in a crash or rollover so it won't keep feeding the flames. I'm not aware of any racing sanction that allows it any other way and it is required "or similar" of all motor vehicle manufacturers.I haven't checked but I would bet its part of the NSRA inspection.

Ok so I like both sides of the coin here...I`m filing this.

Originally Posted by NTFDAY

I agree, nice diagram. One question, what size is the circuit breaker? To require 10 gauge wire the pump would have to draw in the neighborhood of 50 amps and if that is the case that would be one hot pump.

Typically a 30 amp circuit breaker - could use a smaller wire, but I tend to "upsize."

Originally Posted by HWORRELL

Problem is it should be wired thru the oil switch,not to save the engine if it looses oil pressure,but to save your butt in a crash or rollover so it won't keep feeding the flames. I'm not aware of any racing sanction that allows it any other way and it is required "or similar" of all motor vehicle manufacturers.I haven't checked but I would bet its part of the NSRA inspection.

This is a good valid point. If we expand on this to incorporate a roll-over switch to disconnect the entire electrical system rather than an individual componant would be more comprehensive. This is easily done with a continuous-duty solenoid and a factory rollover switch.
For additional security you could lock the solenoid out with a remote transmitter/key fob thing.
But then you get back into the buggaboo of wireing complexities.

Interesting. Food for thought.

I'd never considered roll over protection, or crash disable, but then I'be never built a car for the track.

As for electrical complexity, if it's properly documented, then troubleshooting won't be too painful. My biggest problem is ' brain boxes ' which are expensive and non-repairable.

I can envision a similar circuit, with all discrete components. A toggle switch feeding an on-delay n.c. timer, in parallel with a pressure switch feeding a relay, the relay grounded through a roll over switch. The relay feeds a fused supply to the fuel pump.

I think that circuit will satisfy everyone.

Good feedback guys - one nice thing about the "black box" from Revolution Electronics is it is very simple and inexpensive. About $60 and controlled by a little microprocessor - much like the dozens we use in a lot of automotive applications.

If nothing else, maybe we can all become a bit more mindful of the safety aspect of hooking up all things electric.

Regards All,
Glenn

Glenn, I like the idea of that box, would you have a link for it possibly??? Sounds like something good to incorporate into every build!!!!!

You bet, Dave -http://revolutionelectronics.com/Welcome.html

You can buy them at Classic Industries- Classic Industries | Restoration Parts | Mopar Parts | Camaro Parts | Firebird Parts | Nova Parts | Impala Parts | GM Truck Parts | Tri-Five Chevy Parts

I see the price is up to $65 - but still a good investment in my opinion!

Regards,
Glenn