Power supply design

Hey Zac

Just started on your new wiring course up to power supply design, just want to get your thoughts on a consideration I have with injector power: -

Accurate injector dead time information relies on the ECU seeing the same voltage at it's power supply that a multimeter would see at the injectors so I've always been inclined to take their feed away from the ignition power supply and onto the ECU power supply, shouldn't this be better for AFR stability or non issue? Or only if something else is wrong somewhere else.

An extreme example of this being a thing is on my own favourite platform, the ignition power and injector power are sourced directly from the key barrel, and it's common on Jap imports for some Apexi turbo timer to be installed on that IG+ circuit which for whatever reason back feeds a higher voltage into that circuit causing the engine to run pig rich. Obviously we don't use garbage like that Apexi timer but is there any element of this normally from the other devices in your enable group?

You want your injectors on the same power supply as the ECU.

Only time where you wouldnt use this logic is if using a PDM/PDU.

G'day Mike. I try to decouple the power supply of the new EFI system as much as possible from what was originally in the car, and have the new power supply relays fed from the vehicle battery. This way, there should be very little difference in any of the system supply voltages, as we will have sized the power supply wires to, and from the relays accordingly.

While I can see the logic in having the injectors powered from the same relay as the ECU, I still power them from my 'enable' group relay as I like being able to have just the system ECU's and Loggers active, with none of the rest of the system live.