2G MFI Relay Burning 20 AMP Fuse

[ceasarmo]

Ok, so this is gonna be a doozy and if you stick with me I appreciate it. Also I suck at electrical and this is why I'm asking here.

I have 2g 97 4g63t, the car had a bad engine harness and I sourced a 95 harness and put it on. I made the changes needed to make it work and I followed this guide right here to address the MFI/FuelPump Relay.

The car has been working great for almost a year now, the usual hiccup here and there but running great. I blew the headgasket a couple of weeks ago and I started taking it apart, then back together again. Put it together but I had a misfire at idle, so rechecked the timing and I had a tooth off so back to taking it apart. While it was apart and I had the alternator off I changed the O2 sensor since I could get the socket in there. That's the only sensor I messed with.

Yesterday I was doing the timing stuff, I hooked up the alternator and went to turn it on to see if the miss still was there. So I put the key on, I crank it and then I noticed little bit of smoke coming from the air vents. I panicked, stopped cranking it and took the key off. Following the smoke I noticed it came from the MFI relay specifically, it was burning the harness I made to hook-up those Bosch style relays into the DSM engine harness.

I started unhooking things up, like the stereo, took the ECU out of its place to check if it was rubbing on something, made 100% sure there was no bare wire anywhere on the engine bay, isolated everything, etc.

I replaced the 20amp fuse, went back to crank it and the car starts like a champ, no misfire anymore and it idles perfectly fine. Had it turned on until the fans kicked in, shut it off. I now have to re-do the little harness for they relays since they're crispy but I won't be able to rest if I cant figure out why it was blowing the fuse and burning those cables. And since I did a bunch stuff all at once I don't know specifically what I did to undo the short.

So this is the behavior I was seeing: turn the key to the on position, cables on the MFI relay start getting hot, blow the 20amp fuse labeled as MOTOR on the engine bay. Specifically the cables on the pin 1, pin 3 and pin 4 on the MFI Relay were the ones burning, fuel pump relay is perfectly fine and so are its cables. I found this diagram which tells me pin 1 of the MFI relay goes to the pin 25 of the ECU and then from there it goes to a bunch of sensors, but that's for a 97. Is a 95 the same?

Does anyone have an idea of what cables I should be looking and what cables I should be making 100% sure they're isolated and not touching anything?

 

[Dipwhittle]

The MFI relay usually trips because of a short. Same reason a fuse would blow.

I’d say the problem cleared up because you made sure there were no bare connections or anything in the engine bay.

If it was your radio, the fuse would have blown for that, so I don’t think that’s relevant.

I attached the MFI part of the electrical manual for your car so you can see which wires and components are related if you want to trace it out.