1993 Honda Civic EX 1.6L VTEC 2dr 5spd

Problem: Immediately after turning the key on the 15amp ECU fuse blows which is located in the fuse box under the hood.

We're so far replaced the Main relay and the fuel pump.

This problem has become very expensive in parts and fuses. We've puzzled over the wiring diagram from the service manual for days with no avail. Its a nasty mess. We've also examined the computer itself and appears to be in very good shape (No burn marks, or any other possible issues) to the best of my knowledge. Our next plan of action is to turn the key on without the computer plugged in to see if it pops the fuse and also do the same only without the O2 sensor plugged in. Any other suggestions?

I greatly appreciate any help on this matter.


Thanks!

 

It seems like you have shorted wire to ground on the circuit supported by ECU fuse. I would follow the diagram and disconnect components in that circuit and each check wires with ohm meter to locate shorted wire to the ground.

 

Ok Thanks, we'll give that a shot.

Thanks

 

Reading > me

 

It is 15A hood ECU fuse #31 not fuse 15. Fuse 31 supplies power to the ECU, IACV, fuel injectors, and heater element of the O2 sensor. Unplug each component one at a time to see which prevents fuse 31 from blowing.

 

Fuse #31?

That goes to several things.

Main relay, which powers up the yellow-black wire circuit going to the...
ECU
Fuel injectors
Oxygen sensor heater
Canister Purge solenoid
IACV

 

^I forgot about the EVAP purge solenoid. Also check whether that connector and the IACV connector are swapped.

 

Disconnect battery, and unplug main relay. Test ohms from the black-yellow wire at the relay to ground. You'll probably find it is zero, meaning there is a short. Unplug the parts mentioned above one at a time until the short clears. If it's still there with everything unplugged, the harness must be shorted. Unplug the big harness plugs inbetween the body and the engine to see if it is the body harness or the engine harness.

 

Fuse 31 in the 93 civic ex I have both cables disconnected from the battery and reading 6.5 ohms at the black yellow wire. If I set my meter for continuity check I get a tone. Something doesn't seem right about that and with the battery disconnected should I have continuity anywhere in the main relay connector?

 

Yesterday I disconnected everything except the ECU and turned on the key and checked position 1 and 2 and fuse 31 stayed intact, I then plugged in the main relay and powered up and fuse 31 blew. I replaced fuse 31 and unplugged the main relay and one by one reconnected the injectors o2 sensor and IACV and fuse 31 stayed intact. This pointed to a relay issue so I replaced the relay and fuse 31 blew. The black yellow wire to the main relay reads 6.5 ohms , that is not very much. Suggestions?