Thread: Electric Fuel Pump - 101

Tweet

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.

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.

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.