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ecu back feeding. need some info

Practical Motorsport Wiring - Club Level

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hi all,

i've recently completed my 2nd complete wiring harness: 1 is for an sr20vet using a link g4+ xtreme and the other is for a 4g63 using a link g4+ fury.

i did my power supply design as instructed in the practical wiring course (club level) and i noticed on both jobs i was experiencing what i think was ecu back feeding.

on the sr20 wiring i ended it with the ecu not powering off when i turned the car off. it would power down if i disconnected the VVL solenoid and the ebcs. i'm not sure if i solved the problem using the best solution. i disconnected the main relay from powering the 86 pin of the enabled relay and used an ignition 12V to power the 86 pin of the enabled relay. is this a suitable fix or is it a workaround/shortcut. i ask as i thought you need the main replay to power the 86 pin of the enabled to make sure the system shuts down properly if the main relay fails.

on the 4g63 wiring the coil or the injectors (i'm not sure) starts clicking when i turn the key off. to temporarily solve this i disconnected the ebcs and the the clicking stopped.

so the question(s) is: do i apply the same logic as i used on the sr20 wiring?

what should i do different in the future to avoid these situations?

do i wire the power supply as link instructed in the help file and ignore the power supply design in the course?

i hope i'm not asking to much or being a pain. thank you

Im not sure how the power supply is drawn in the course, but the important thing is that the +12V supply to anything connected to an aux output (or injector output on ECU's with P&H inj drives) must turn off at the same time as the ECU power supply. In your case it sounds like possibly the 12V side of the EBC or VVT solenoid was still powered up when ignition was off.

Thanks for the reply Adam. What are my possible solutions here. I'll test and see if i still have the vvl solenoid powered up. Thinking ahead here, if it isn't that's a good think. My next question is, what could i do to have my main relay back in control of my entire efi system?

On the flip side if i test and the solenoid is still powered, how do i remedy that?

I'm really trying to wrap my head around this issue so that in future i could avoid it from the start

Attached Files

Your original power supply sketch should work fine and it follows how Link recommends it is done. Your symptoms suggest however something in your wiring doesnt actually match that sketch. I have wired them as per both of your sketch options and have never had a problem.

Thanks again for your reply Adam. i checked the VVL solenoid and the EBCS for power when switched off. both register about 0.1V when the system is turned off.

i switched from my original sketch to the adjusted sketch and on the surface of it my problem was solved. is my adjusted sketch recommended? does this ecu back feeding have anything to do with the fact that both ecus in question have peak and hold injectors drivers?

lastly, could i power both the 86 and the 30 pin of my main relay using the ignition switched 12V as in this attached sketch below?

Attached Files

Hi Gerard, that's a weird issue since as Adam has mentioned, your original diagram should have been correct. The issue you'll often see is that the AUX outputs on the ECU will pull to ground when the ECU isn't powered up which then keeps the relays latched if they are supplied power from the battery or the ignition switch. As a matter of course I always supply the switching power to other ECU operated relays from the main ECU power. This way there's no chance of the relay =operating unless the ECU is also powered up.

Thank you Andre for your reply. Are you recommending that i connect pin 87 of the main relay to pin 86 of my enabled relay? Also, could i supply both pin 86 and pin 30 of my main relay with power from the ignition switch?

did you ever get to the bottom of this? i am currently having this exact issue and i followed the example like the op did? if i pull the fuse to the solenoids it works as it should

Can you provide a sketch of your main power circuits.

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