<VV> Electric pump control circuits

[Sethracer at aol.com]

The Monthly "Electric Fuel Pump" question brought another few questions to  
mind. Someone already mentioned adding a switch under the dash or in the 
glove  compartment to use the pump only when needed. Let us leave alone the 
question of  "Why an electric at all?". There are a few advantages to an 
electric, and a few  drawbacks. New cars which use electric pumps, which is to 
say ALL cars, have  other circuits added to improve the safety of operation. 
With an electric pump,  there is no pressure in the fuel line on engine start 
up. The electric will  supply it after a few seconds. With fuel injection - 
again ALL new cars - you  need a high pressure and that must be a stable 
constant high pressure. That is  not needed with carbs, not only is the fuel 
pressure much lower, you are only  refilling the float bowls, not directly 
feeding an electrically controller  injector, but the volume of fuel is 
usually less, because there is no return  line - as used on most, but not all EFI 
systems. So an EFI pump is controlled  electrically, by a few circuits. 
There is a relay that turns on the pump at  start up and based on needed 
pressure, turns the pump on and off. On many cars  there is a pressure switch that 
cuts electric power to the switch if oil  pressure drops, usually an 
indicator of the engine no longer running - despite  the ignition switch still 
being on, on other models, a switch is in place that  cuts off the power to the 
pump if a certain shock load is fed to the car, like  an accident or (in my 
case) a blowout of a tire at speed. 
My question - Does anybody know of a combination switch, preferably one  
that mounts in the engine compartment, that will respond both to the oil  
pressure feed and the shock load, and cut off the pump power feed if either one  
applies?
 
- Seth Emerson 
 


Seth Emerson

C's the Day! -  Corvair, Camaro, Corvette
San Jose, CA