1G 20A MPI fuse keeps blowing

[thakingcb7]

Ok so there's the story.

Started the car this morning so I could get a log with my newly installed wideband. Fired up fine and even drove fine. I did a quick 3rd gear pull on my way to the highway and everything was fine. Problem happened when I got on the highway and did a short pull in second to get up to speed. Started off pulling real nice and smooth but out of nowhere, power died. I coasted off the highway and began looking around. MPI fuse was blown. Went to the parts store and bought the 2 they had in stock and blew both of them. Bought 3 more at another store and started cutting wideband wires (it was literally the only thing that has changed in the past few months). Started by cutting the wire that ties into the ECU, first fuse popped. Next I cut the ground, second fuse popped. Unhooked power so the wideband was completely eliminated as the cause and the third fuse died.

I'm completely lost at this point. Everything was fine one second and now it's dead the next.

 

[brads]

Do you have a multimeter, or other way to check for shorts that doesn't require popping in more fuses?

 

[thakingcb7]

No multimeter but I'm gonna start checking all the wires in around the ecu. I gotta wait a few days for new fuses to come in so I'm in no hurry.

 

[steve]

I'd suggest getting a multimeter you'll use it enough to pay for it's self. Heck 5 blown fuses would have paid for a cheap one already. Another useful tool is something like a tail light socket and bulb with alligator clips that you can connect in place of the fuse. If it lights up bright you have a short downstream.

The MPI circuit powers much of the engine bay so finding the problem will be a process of elimination.

When does the fuse blow? When it's first put in or when you turn of the ignition switch?

Disconnecting the ECU should keep the MPI relay from activating so you can see if the problem is before or after the relay.

You're going to need the electrical wiring diagrams, the 90's are slightly different so keep an eye out.
https://www.mediafire.com/folder/5k14qlaulb9s1/dsm_mitsubishi

 

[steve]

What did it turn out to be?

 

[thakingcb7]

Umm... honestly, I'm still not 100% sure. I unraveled the taping that my buddy did and retape differently and it fired right up. Thinking maybe it was somehow causing some kind of interference and blowing the fuse.

 

[bling5tatus]

I'd inspect the connections your friend made and how well they were insulated.

 

[thakingcb7]

All the other ones were good. The one at the ECU was the only one I didn't supervise because I was installing the sensor into the O2 housing.