Electric Fuel Pump Review

[John76]

This is Rev 3 of my electric fuel pump wiring diagram.

The addition of an oil pressure safety switch and/or inertia switch is a prudent safety measure.

I also realized that the trigger source to the pump relay (terminal #86) should be from an unfused ignition source....just like the coil.

If the traditional Green/White wire from the fused side is used (as shown in the fuse diagram) then the fuel pump would stop if the #12 fuse blew!

So, my thought is:  If you have ignition (spark) and oil pressure (to safely switch) and you haven't crashed (inertia switch)…. then you will get gas.

Review and comments would be appreciated.

Thanks,

John

PS: The trigger voltage to the #86 tab on the relay can be as low as 8 volts, so no problem with a resistor-wire or + coil source.

 

[2002]

If fuel pump stops working you will have fuel in the carb for a while, so does it matter?

[AustrianVespaGuy]

Looks really good, well thought out! I especially like additional indicator light to let you know it's getting power, a nice touch! And @2002, it matters because if you're in an accident that causes both a torn/ruptured fuel line and a fire, you don't want the pump to continue pumping raw fuel TO the fire!

[uai]

Yes, that's all correct, but why not just use a fuel pump relay for less than 20 bucks.

It will deliver current to the pump for priming without a running engine for a short amount of time after it gets 15.
If the engine stops it stops delivering after some seconds.

No need to get an extra oil pressure switch, switch, control light etc.

 

 

 

[John76]

13 hours ago, 2002 said:

If fuel pump stops working.....

 

You don't want the pump to stop just because a fuse blows. Why run out of gas if the electric choke wire falls off and shorts to ground?

I believe this is why the +12V wire to the coil is not fused.

 

I always thought:  "the pump don't work cuz the vandals took the handles"...…..Bob Dylan.

 

2 hours ago, uai said:

why not just use a fuel pump relay

 

Great idea! I didn't know such a relay existed.  I only play with the relays that came with our cars.

Can you provide a connection diagram?

[AustrianVespaGuy]

Megasquirt controls my FP in a very similar manner to that relay.  It relies on seeing a valid tach signal in order to know that the engine is 'running.'  This is in essence just as good as a oil pressure switch, but on the other hand neither of these is QUITE as good as an inertial cutoff switch either.  For me I consider it safe enough for the given car, but for the highly safety-conscience, adding an inertial switch in line with such a fuel pump relay would really cover all the bases.

[uai]

3 hours ago, John76 said:

Great idea! I didn't know such a relay existed.  I only play with the relays that came with our cars.

Can you provide a connection diagram?

15 is ignition (switched +)
30 is Bat +

87 is + to the fuel pump

1 comes from 1 at the coil/distributor

31 is ground

 

I only found this diagram where 31b is equivqalent to 1 of the above relay

As long as 1 is "alive and pulsing" the relay is closed. When 1 stops pulsing the relay stops after a few seconds.

When 15 is applied the relay runs for a couple of seconds (priming) and then waits for the pulsing

 

Edited April 3, 2020 by uai