ECU turns on when I turn on power for ignition and injections

Hi,

I am using ECUMASTER PMU16 to power PRO8 ECU, I use an Output 15A for ECU and ADU only, and use an 25A output(engine power) to power ingition(3pin), injection(2pin), E85 sensor(3pin),O2 sensor, VVT(2pin), and boost control solenoid(not connected yet).

The problem is even when I plug off the power supply wire to ECU, after I turn on engine power, the ECU turns on, throttle body starts to buzz and there is a -12V voltage on ECU's power supply pin! And because ECU and ADU's power supply pins are connected together, I can also see ADU bilnk with low light(like no enough power to start).

Then I plug off all connectors on ECU and turns on engine power supply only, and tested all pins. I found there is 12V voltage on output pins for injection and VVT, I assume this is normal? And 12V on input pin for E85, O2 sensor, crankshaft position sensor both + and -(when I turn off engine power, there is no voltage), is that normal??

The engine can start, nothing happens when I turn both ECU and engine power on. So no wire is connecting wrong I think. Just when I turn off ECU power but not engine power, ECU will stay on, and when I only turn on engine power, ECU turns on, which is really annoying.

Please tell me what is normal and what is not, what caused this problem and how to solve it.(probably the easiest way is combine ECU power and engine power together to a single output?)

Thanks!!!

Jimmy

You are back-feeding power into the ECU. In order to avoid damaging the ECU, you should arrange your logic so the ECU power is always on before your Ignition/Injection power can be applied.

For most race cars, the ECU turns on with the master switch (or main dash power switch). The Ignition Switch (or Run/Stop) is only enabled if the master switch has been turned on.

Hi David,

So what I should do is avoid turn off ECU power before I turn off ignition power, right?

For my wiring arrangement, this back feeding symptom is expected?

Yes, ECU is first to turn on, and last to turn off. Or you could turn them both on/off together.

I don't know the details of the PRO8 ECU. But often powering circuits that are controlled by outputs can result in back-feeding power into the ECU. So it's something to be aware of. Biggest source is usually things like fuel pump or fan relays.

If there's "back feeding", assuming we're thinking of the same thing, using a diode of the correct current rating for the 'forward' amperage, should prevent it.

As David suggests, it's more common to turn the ECU on before, or at the same time - is there a particular reason for doing your way?

Thanks David, problem resolved.

Hi Gord, there is no particular reason for doing this, just I didn't know if one 25A output will be enough to power them all, so I split them into to two power lines.