So I am finishing up the last few things on my EJ swap into my 84 wagon.

 

Got her running pretty nice.......still needs exhaust, temp corrected with a resitor, and an oil pressure sender.....but I digress......

 

The biggest problem I have....is that when I hook up hte ECU's "backup" power supply.....the engine actually runs rougher......and whn I turn off teh key.....I have power backfeeding to my dash and headlights. (warning lights dim, and the headlights have power to turn on fairly dim)

 

The engine runs great without that wirre hooked up, but I'd like to know what the deal is.

 

The Original Diode is in place on the EJ harness......But that diode is for a different power supply(Ig. switched from ALT-2)

 

The wire in question is shown in the diagrahhms as not going through a diode though......FSM shows it coming straight from battery volts through fuse 14.

 

Do I need to install a diode on that wire?

 

Harness and ECU are from 93 Legacy auto......any advice appreciated.

Wire in question is YR from pin A15 on the ECU.

Edited January 15, 201016 yr by Gloyale

Since you've seen some Subaru diodes - is there any chance of taking a picture of one, I'm curious what they look like and how they're wired in since I suspect that is causing a problem.

 

Anyway - diodes prevent backfeed so sounds like you're on the right track for fixing it, though I have no clue how to proceed from there.

 

Testing another stock EJ isn't an option is it? I'm not quite seeing the exact issue/wire, but maybe comparing current would help?

something is definitely not right. I'm surprised it even runs without that hooked up.

 

as you mentioned, the diode is for a different circuit entirely. so it shouldn't effect it. the diode allows the ECU to shut off the main relay if it needs to (never seen it happen....but it's called the Self-shutoff control....). In the swap on my Loyale, I completely removed the diode. hooked the main relay up to the switched source from the car, and then gave the ECU switched power sources where it needed it. worked great for many years (and still is working).

 

 

Where are you getting your constant 12v source for the backup power? have you tested it to make sure it's all of 12v? have you checked all the grounds at the ECU to make sure you're not getting too much resistance.

So, I installed a diode on that circuit. And all is fine. Except now I have 24v on that wire.

 

Still runs great.

 

Any more thoughts?

 

That wire is labeled "back-up power supply" in the FSM. And it had 12v on it before I wired it to fuse 12v through a diode (sucsesfully preventing the backfeed but....)

 

Could that wire be supposed to actually feed power to something else ?

 

Chux, I will definately be checking my grounds.

All grounds check out.

 

Still running fine.

 

It just un-nerves me that there is 24v on that wire, and without the diode I installed, it would be backfeeding power to my lights.

 

Has anyone else run into this? Particularly the backfeed issue?

 

It makes me wonder if it's somehow related to my Alt wiring?