1G MPI fire, troubleshooting help

[mikus]

I was dialing in some stuff in ECMlink this AM and a bit of smoke starts coming out of dash. Pull battery! poke around and find the MPI relay is melted.
- Pin 10 (black w/red stripe) appears to be source, melted bigtime
- MPI relay internals look sound
- ECU looks fine, I see no damage anywhere

I tested pin 10 in MPI harness and got ground continuity intermittently so figure OK, short, fixable.

I tested the rest of the pins on harness and all are also ground except for 7&8? That doesn't seem right to me at all

Car is at Starbucks, really rather it be in my garage - any temporary or permanent help appreciated. Grabbing MPI & clean wire harness tomorrow.

 

[steve]

I was dialing in some stuff in ECMlink this AM and a bit of smoke starts coming out of dash. Pull battery! poke around and find the MPI relay is melted.

I tested the rest of the pins on harness and all are also ground except for 7&8? That doesn't seem right to me at all

That's not right. It might have something to do with how you measured those as ground or might explain why the incoming power wire melted but I would have hoped the MPI fuse would blow first.

Only pins 4, 5, and 8 have anything to do with 10.

Normally power is provided from the MPI fuse to pin 10, the relay has a blocking diode going from pin 10 to the coil for this relay (there are two in a 1G MPI relay box). The other side of the coil is connected to pin 8 and runs to the ECU. The ECU pulls pin 8 low causing current to flow activating the relay. This switches pin 10 to pins 4 and 5. They go to the sensors and solenoids on the engine. It sounds like you have a short or failed part in the engine bay connected to the MPI circuit.

 

[Infamous33]

Following steve's lead... Pin 10 comes from the 20A fuse (sub fuse link B) and it passes through connector A-08 at pin #4, which is a 10 pin connector located near the relay box.
I was thinking that wire must have shorted itself to another wire or a pin in the connector, as it is a power feed and that lil 20A should have blown long before the wire/connector melted.