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Ecu backfeeding issue

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals


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Hi guys, so i have built and installed my first harness and power supply and am having an issue with the ecu staying on once ignition is turned off. I have wired my relays as told to in the further considerations video in the course so am quite confused about how the ecu is still getting power once ignition is off. I have attached my diagram for my power supply section, also have found that if i remove the aux solenoid fuse then the ecu shuts down. Any help appreciated!!

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something i found interesting is while troubleshooting the problem i decided to pull the ECU relay whilst it was powered on (i figured surely if the relay is out even with the backfeeding issue then the AUX relay should surely lose 12V power? however the ecu stayed powered on. Does this mean that the AUX relay is staying energised purely because of the baackfeed into its own 87 pin? If so I dont know how to get around this issue

Why don't you remove the ECU, and see which pins on the ECU connector have power on them with the ignition off and the ECU relay removed. Those are the sources of your back-fed power.

I have found the sources, they are my VVT solenoid and ISC solenoid. This issue only happens when either one of them are plugged in. The wiring for them is correct so I dont know how they are causing this issue to be honest. I have called link ECU and they dont have too much advice for me to troubleshoot the situation. Mainly saying that there must be a backfeed coming from somewhere else, I dont see how it could be from anywhere else though if it is only happening when I plug either the ISC or VVT solenoid in

What other relay coils are powered from the main ECU relay (the ones that are cut off the right side of your drawing)? Fuel pump? Fans? Have you tried with all other relays out leaving only the ecu and Ign one in?

Note, dont just focus on it being the ISC or VVT - they are obviously auxes with flyback diodes so are part of the problem but the root of that relay staying pulled in is what you need to find.

I normally do it slightly different like below, which I think is a bit more fool proof. If it isnt a big job to change yours it will probably solve the problem.