Fuel pump trigger activated when power is removed from ECU?

[B1ack_Mi16]

Noticed this strange thing with the Engine management light, that it would stay on in a dimmed mode when I turned ignition off.
See movie here where ignition is on and then turned off:

http://vid428.photobucket.com/albums/qq ... ianm32.mp4

After some investigation I have found that the Fuel Pump output actually seem to activate when the ECU is switched off.
Should it be like that? At least that's what happens, FP output earths when I turn ignition off...

I've used a standard factory engine management loom as basis, where power is provided to sensors/coil/injectors through a multirelay as seen in the figure below.



The relay is triggered by the factory ECU with ground to pin 7 and 10.
While pin 14 has a constant +12v feed, and pin 3 only has +12v feed when ignition is on.

Anyway, what happens is that when I turn ignition off, pin 14 still has +12v as it is a constant feed. Then MS3 Pro grounds the Fuel Pump ooutput, and the m ultirelay activates +12v power feed to quite a few sensors/injectors/coils.

It seem to me that somehow this +12v feed manages to partly keep the ECU alive (as PC connection is only partly lost, and flickers), in addition the engine management light is dimmed as shown in the movie.

Any ideas how to fix this? I know I possibly just can change the Pin 14 of the relay to be switched +12v, but I was hoping to avoid modifications to the loom.

[nathaninwa]

I had this same problem from having another Ecu in the car. I jumpers constant hot to the pump over to the trigger portion. The other Ecu didn't mind, but megasquirt can't have the feedback or the unit won't shut off. Make sure that the trigger side of the relay has switched 12v power from the ignition switch.

You might be able to use a diode on the fuel pump trigger ground on the Pro wire so 12v+ can't back feed

[B1ack_Mi16]

Feeling a bit silly now, I notice it's even mentioned in the manual for the FP trigger that it can back-feed.

Well, then I'll have to butcher the loom a little bit anyway I guess.

Edit: Maybe this output should have a diode installed onto the MS3 Pro board for future versions?

[B1ack_Mi16]

One more related question.

I'm controlling the cooling fans using PWM1 and PWM3 outputs.
PWM1 will trigger slow speed mode with fans in serial.
PWM3 will trigger parallell mode.

However the relay related to the slow speed mode for PWM1 has also a constant positive (+) feed to it's coil, just to be fed negative to activate.

Does the same apply here, that I need to make sure the positive feed to the relay is switched?

I guess the reason for why it is wired like this is that it shall be possible to trigger the cooling fans even when the engine is not running.

And reason I ask is that now after I fixed the multirelay issue so that one is definately switched (+) the fans starts running when ignition is off.

[nathaninwa]

I can get this one too! Yes. I'm using a pwm output to control a solid state relay for my cooling fan. I wired switched positive to the accessory side of the key so that the fan would shut off while starting. Well, turn the car and the fan runs till I hit the ignition side of the key switch that turns ms on