Hi All,
I'm starting to think about how to wire my fuel pumps. I have both a low and high pressure pumps, which will be switched from the megasquirt.

MSExtra Diag Here

My plan was to just run an additional fuse from from the relay'ed feed to the 2nd pump, which is easy enough.

But I would also like to run an inertia switch to cut them both out in the event of a bump. I'm planning on putting this switch inline with the megasquirt to fuel pump relay feed (the green wire on the diag).

Can anyone see an issue with this?

I assume the LP pump is feeding a swirl pot, not a big problem but, you will need to prime the swirl pot somehow, the MS feed only fires a short priming pulse, then doesn't run the HP pump until you crank the engine. When I had MS, I just created a seperate Ignition feed for my LP pump (fused and relay of course)

Just my 2p worth

Whenever I've done this in the past I've wired the lift pump (low pressure pump) to the normal switched live from the ignition and the high pressure pump from the megasquirt. That way the swirl pot can be primed so that the high pressure pump doesn't suck up air, which can be fatal on older ones.

It's also worth trying to ensure that the low pressure feed into the swirl pot is higher than the high pressure outlet, especially if the swirl pot is higher than the regular tank. That way if you get any kind of syphon starting up when the pumps are off it can't drain the swirl pot down to a point where there is no fuel available at startup.

Chris

A very good point about priming, something I hadnt thought about.