hi all

i am only just getting round to wiring in an inertia fuel pump cut off, my fuel system has two fuel pumps a low pressure feeding the swirl pot and then a high pressure after. the problem is the HP pump is controlled by the megasquirt and the the low is on as soon as the ignition is turned on so this way i would need to put the inertia switch on the main ignition key circuit but i dont think the switch is up to the job.

can i wire the LP pump to the HP power supply from the ecu so it would come on when exactly the same time the HP pump has done, would this be ok?

realise it may be a daft question but just wondering what peoples views are before i start to do this

Regards

Mark

If you use Megasquirt to pull in a relay from the pump signal then you could power each pump from the relay contacts.

The transistor inside megasquirt is not rated very highly and the ECu is usually modified to switch an internal relay because of this.

If your megasquirt has this mod it may be ok but not worth the risk, i would insert another relay to switch the pumps.

Each pump could then be switched through seperate contactson the relay from seperate fuses if you wanted to arrange it like this.

Sorry yes forgot to say the megasquirt is connected to a relay to power the HP fuel pump so that should be ok then ?

Yes, that should be OK. You might need to bridge the fuel pump relay before initial startup though to fill up your swirl pot.

Having just converted to EFI I already had a cut off switch at the rear for the low pressur pump so I just added a second one at the front for the high pressure pump.

i have my low pressure pump and high pressure pump running off the same relay, controlled by megasquirt. it works ok but you need to be cleaver how its all hooked up.


you need to make sure the fuel rail return goes back to the swirl pot not the tank. if you ever run out of fuel you will need to turn the ignition on and off 4-5 times to fill the swirl pot before trying to start. other than that there is not much else to worry about as long as your power cable can handle the current for both pumps at the same time.

When I converted to EFI, I did this :-

1) LP pump relay runs of switched feed (as before) so is on the whole time
2) HP pump relay is controlled by MS
3) Inertia switch between HP relay and HP pump.

thanks guys thats what i will do my swirl pot has the return going into it so should really remain almost full most of the time.

i was a bit worried about connecting up the inertia switch just to the HP pump and not LP because what if a fuel line fractures in a crash although not at 50psi there will still be running fuel at 5psi being pumped

good thing is aswel both pumps are fairly close so wiring not a problem may stick a switch in aswel incase i ever do run out of fuel or need to prime the swirl pot

thanks very much for all your suggestions

Mark