1962 electric fuel pump for F.I.

[Richard L.]

In order to avoid undue cranking while waiting for the Injector to fill on my 62 FI car, I'm considering inserting an in-line electric fuel pump to supplement to the original mechanical one. An additional benefit with a steadier and fuller fuel flow might also keep the Injector cooler and thus avoid percolating in 90 degree summer temperatures. I know that other manufacturers of the 1950's such as M-B equipped their high performers --think 300SL Gullwing-- with both pumps.
Any constructive thoughts on this as guidance for me?
thx
Ric

[Dan H.]

Hi Richard, do you have an electric shut off valve to prevent fuel siphoning? If so, this can cause a delay in fuel being sent to the nozzles by the FI units gear pump. Your engine fuel pump should be primed all the time by the fuel tank line, so an additional third pump is unneeded. Hopefully your FI units fuel bowl is not draining after sitting causing the lag in start up. Check number 8 spark plug and see if it's wet from leakage etc. Your start up fuel comes from the fuel bowl and gear pump. Check you original system, it should work fine.
Dan

[Jim L.]

Richard, I can't think of any reduction in the tendency for fuel percolation that would come from adding a pump in series with the existing engine mounted pump.

Think of it this way.... as long as fuel continues to pass through the hot, engine mounted pump, it will continue to pick up heat and to experience an increase in temperature.

If you want a perc-mitigation benefit from that electric pump, then bypass the engine mounted pump entirely. Let the electric pump be the only supplier of fuel to the FI unit.

[Richard L.]

Thanks guys, what you say does make sense.
Jim, it never occurred to me that the mechanical pump would add much heat to the fuel passing through it, some yes, but not a lot. At any rate, even a few degrees do make a difference when it's above 90 outdoors.
Happy 4th!

[Jim L.]

Thanks guys, what you say does make sense.
Jim, it never occurred to me that the mechanical pump would add much heat to the fuel passing through it, some yes, but not a lot. At any rate, even a few degrees do make a difference when it's above 90 outdoors.
Happy 4th!

Think about it this way, Richard: There will be ounces of fuel loitering in a hot chamber attached to a 500 lb. lump of hot iron. The slower you drive, say, in stop and go traffic, the longer the fuel loiters. A significant increase in fuel temperature is inevitable.

In any event it doesn't have to be above 90F for fuel perc to be a problem.

Here on the left coast the RFG we use will begin to vaporize in winter at fuel temps around 105F and in summer at fuel temps around 140F. Such underhood temperatures are easily achievable at ambient temps around 65F and 80F respectively.

What this means is that anything which reduces the temperature of the fuel reaching the FI will help to reduce or delay the tendency for fuel perc.