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Multiple relays running from fuel pump drive?
Posted: Wed Apr 27, 2011 1:25 am
by agw_01
Can pin 37 of MS (fuel pump relay drive) be used to trigger 2 relays? The wiring diagram shows only the fuel pump relay using pin 37, whereas the main relay is on a switched live.
I currently have the fuel pump relay on my car triggered through pin 37. The issue I now have is that my main relay gets a permanent live through the fuse box. Can I use a switched earth (pin 37) to trigger both the main and fuel relays?
Didn't want to go ahead and do it if the board can't handle it.
Re: Multiple relays running from fuel pump drive?
Posted: Wed Apr 27, 2011 1:58 am
by agw_01
Just to add, the ECU gets power from another source as soon as the ignition is turned on.
It's only the injectors and stepper motor that are left on the main relay.
Although from what I've been reading, MS turns on the pump relay for a few seconds when the ignition is switched on and then turns it off until it detects a tach signal. Would this be enough time for MS to adjust the stepper before cranking?
Re: Multiple relays running from fuel pump drive?
Posted: Wed Apr 27, 2011 8:15 am
by patrickbrown
The injectors and the ECU on the main relay should be switched by your key. What stepper motor are you talking about? IAC?
Re: Multiple relays running from fuel pump drive?
Posted: Wed Apr 27, 2011 11:23 pm
by agw_01
Hi Patrick, thanks for the reply.
From what I can make out looking at the wiring diagram for the car (1994 Rover 420 Turbo) power is permanently applied to the main relay through pins 30 and 86. Pin 85 goes to the ECU to a pin marked 'main relay drive'.
The ECU has a pin marked 'ignition sense' so I presume when it gets power through the ignition sense wire, it grounds the 'main relay drive' pin.
Pin 86 of the fuel pump relay also gets a positive signal from the 'ignition sense' wire and has another pin on the ECU which I imagine switches to ground when the ECU is powered on.
Pins 30 and 86 of the main relay are ran through traces in the fusebox so no way I can get in there to cut any wires etc.
Megasquirt is in the car on a switched live which also runs through an immobiliser. And yep, sorry, I meant the IAC. Will the 'prime' be long enough for the IAC to reset before I start cranking?
Thanks.
MSII on a V3 board if it makes any difference.
Re: Multiple relays running from fuel pump drive?
Posted: Thu Apr 28, 2011 12:35 am
by trakkies
The pump relay driver transistor is a XTZ 450 which is a one amp type. This will happily drive two standard relays.