Charchee

On my 89 4Runner 3.0, which is set up a little different from yours, the power supply wire / fusable link is the only power supply to the box. If you are going in there to find your issue, let me make a suggestion. Replace that supply wire with something nice and big. I find it hard to believe that they would have designed this system with such a small feed wire from the factory and am puzzled why they would put a fusable link in such a short wire that is just feeding fuses and relays. Seems kind of redundant. Take a look at this thread. I thought there was a better one out there with more pictures. I did this mod on mine and have seen improvements in my electrical system as a whole. https://www.yotatech.com/forums/f116...y-wire-208951/

Here is a picture of my wire. I believe I used a 6 gauge.

Dk2685

So I replaced the 80a alternator fuse and things have progressed a bit. Still not getting the truck to run but I now have .34 volts from B+ to batt- and from the efi fuse terminal to batt-. The efi relay terminals are still reading the same

Charchee

What kind of voltage did you have at that 80A fuse socket? That's where the power supply feeds into first. Low voltage there would indicate a bad supply wire. Will your headlights come on?

Dk2685

ive got 11.80v to where the fusible link connects to the 80a fuse. The headlights will come on though a bit dim. Previous owner installed aftermarket headlights (perhaps by themselves) but all that wiring looks pretty sound.

in other news, the wire harnesses going into the ignition coil are a little melted looking...

Dk2685

I found some melted wiring housing going to the ignition coil and to the alternator but most of the wiring inside the housing looks decent. Nothing broken or shorting. The alternator is getting 11.8v so I've ruled that out as the problem but the coil is not powered. I found a wiring diagram for the 3vze but I'm unsure exactly how to determine what lies between the efi fuse and the coil. Any thoughts?

http://www.snjschmidt.com/wiring/Engine_Control_3vze_2.jpg

Charchee

The alternator is part of the charging circuit so it's going to have voltage all the time. Did you ever get power to the EFI fuse? If not, you're on the wrong side of the truck. It will never start or even attempt to until you have power to the EFI circuit. Everything depends on it.

Dk2685

i didn't get power there. Just went down a rabbit hole trying to investigate some melted stuff near the ignition coil. Maybe I'm getting desperate?

Dk2685

I may have found the issue! I determined that one of the green and black wires from the efi fuse is going to the ECU. I took off the front and back panels of the efi and found some burnt out diodes. I think I'm gonna try and find a used unit on eBay and pop it in. Any advise before I make that purchase? It isn't possible to repair the circuit board is it?

scope103

Circuit boards can always be repaired. Figuring out WHAT to repair is the trick. If you have two diodes that are actually burnt, I wouldn't be surprised if you took something else with it.

BUT: the EFI fuse powers the ECM, not the other way around. If you don't have 12v on the EFI fuse, then you're got going to get power to a brand-new ECM. I suppose it's possible that your ECM has a dead short in it, but that would immediately blow the EFI fuse, and you think that's good.

Dk2685

do you have an idea of what lies between the battery and the efi fuse? I really haven't been able to track down what is happening there. Should I change my fusible link just in case?

scope103

Uh, a piece of wire?

My EWD is for a '94, so yours might be slightly different. On the '94, the EFI fuse connects (electrically) directly to battery; there are no other fuses on the way. On mine, the EFI fuse is only about 5" from the battery side of the fuse block. The "outbound" wiring is through two large connectors, so if yours is similar you could gently pull those connectors, remove two screws holding the fuse block, and find whatever the problem is.

Charchee

Did you ever get power to the EFI fuse? It sounds like you haven't unless I have missed something. If not, that is the one and only problem that you know you have and no amount of work beyond that point is going to get it running. My wiring harness is brittle, burned looking and bothers me to look at it but everything works. I have a like new one hanging on the wall for when mine craps out but it's not going on until my current one has an issue that's going to be a lot of trouble to repair. What I'm saying is that just because something looks burnt or otherwise bad, it doesn't mean you're looking at your EFI problem and need to replace / repair the part. Your ECM may well be burned out but you won't be able to confirm that until you have power to it.