In desperate need of advice! Had my obd1 b18 idling in my 91 hatch and then there were some sparks from under the dash and the car totally died. no power to anything. found the main battery fuse and ecu fuse blown along with a couple of others under the dash. Replaced all of them but now the ecu fuse blows immediately whenever the car is turned on. The fuse only blows when wires a13 and a15 (main relay power wires) are plugged into the ecu. When the fuse is not burnt out, both wires have voltage at the ecu plug. The ecu fuse will blow even when the only wires plugged into the ecu are a13, a15, and the A plug grounds. I think that this has to mean the ECU somehow got burnt out. I had some things wired into it wrong (distributor and injectors) when I converted from dpfi and I think I might have damaged it. PLEASE respond to this if you have any insight, I am at my wits end. I am afraid to buy another ecu and plug it in case I have another huge short that blows it out again. I tested the main relay out of the car multiple times and it works but does not click when plugged in. All the grounds seem to be good. I am in the process of inspecting the fusebox area for obvious melting, exposed wires, etc. ANY ADVICE APPRECIATED.

(Another consideration is that when the car was running I had the injectors powered by a fused line coming right from the battery because the injector power from the main relay was not working.)

 

I would start by double checking your wiring and pulling the case off the ECU and see if any of the leads coming off the connector are burnt/melted. You can also check the circuit boards to see if any capacitors or resistors are popped

When you used different main relays, did the ECU fuse blow? Were you able to start the car? Your main relay might be bad or wiring to the main relay could be fried.

I would also check the amps coming off those wires, just make sure your meter can read high enough amps or you will burn it out.

What fuses burnt under the dash? Were they related or random fuses?

"(Another consideration is that when the car was running I had the injectors powered by a fused line coming right from the battery because the injector power from the main relay was not working.)" Did you revert this to the normal circuit? or kept it as is?

 

If your ECU fuse is blown your main relay won't get power anyways. You can jump the pins to get power to the fuel pump, but thats about it. If you are worried about the main relay, bench test it with a battery and a multimeter. There is a section about this in any ef shop manual.

If the car ran before I would check the harness for exposed wires. That could be causing a short.

If you want to figure out if something is not grounding out correctly because you touched the harness, I recommend this:
-Unplug the harness from the car and ecu
-Check for grounds:
-Any gound rings
-Shielded wires for the distributor
-Fan switch
-There are some ground pins on the ecu plugs. I cant remember what pins they are.

Just make sure there isn't power going to where grounds are supposed to be going. There may be more but these are off the top of my head.

 

Solved! I picked up another ecu and almost all the issues went away. Somehow the old ecu was grounding out the power from the main relay and blowing the ecu fuse. I opened up the old ecu but could not see any obvious signs of overheating. I had the ignition switch unscrewed from the lock cylinder and I think that one of the solders on the power wires grounded out on a pedal or something. The only remaining issues are a check engine light for the 02 sensor and an extremely high idle (2500 - 3000 rpms). I tightened down the valve in the fitv and I'm going to check for vacuum leaks in a sec. Thanks all for the help.