MPI / ECU help -- updated! MPI fire

[mikus]

Joined the VR4 Fire cru this AM...
I was messing around tuning 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
- MPI relay internals look sound
- ECU looks fine at a glance

I tested pin 10 in MPI harness and it's grounded, shows continuity intermittently with cig lighter frame and ECU ground.

ECU looks fine, IC110 looks fine, for what I can tell.

I figured to just run a new fused +12V to pin 10 and new MPI relay to get it home, BUT on testing other pins on harness I have ground continuity on 2/3/4/5/6/9 (key off) too? That seems wrong so am nervous to proceed.

Here's a schematic and MPI testing steps.
Applying +12v to pin 10 and the ground (-battery) connection to pin 8 should make 12v show up at pins 4 and 5. Same deal for pin 3 and 7 causing 12v to show at pin 2.
Applying 12v across pins 9 and 6 will cause continuity between pins 3 and 2.

 

[Yao]

Hopfully it's a short somewhere and the MPI fuese too the hit instead of ECU, but then on the other hand, if it's ECU, just replace. Where as if it's a short somewhere, you are gonna have to spend time hunting it down..

 

[mikus]

moved content to original post

 

[mikus]

updated original post with DMM testing and cleaned up some. No clue what to make of all this, any help is appreciated

 

[chrisfullwood]

i would think it is safe to say, that if all the pins (or most of them) are reading grounded, then the relay is fused, and will need to be replaced. If i get time tomorrow, ill look over the various schematics, and see if i can come up with anything to help out.

do you have any other signs or symptoms?

 

[mikus]

the relay isn't connected, they're grounded when testing at the MPI harness! I've tested with two meters and two ground sources.

Other symptoms (or lack thereof heh)
- aftermarket: various piggyback sh*t has been on ecu wiring before. I've gone through it all previously to clean up and felt it was pretty good. All solder no crimp.

- I can't think of anything shoddy on the MPI line (ISC, injectors, MAF etc) The maf does have a maft piggybacked, but it all looks OK too.

- Car was running fine, daily driven Ie. this was sudden /unrelated. Car vibrates a lot. both support short theory to me.

- MPI clearly is clearly burnt at pin10, no doubt about it. Harness was so burnt, pin10 wire literally 'broke off' of harness when I handled it. Batt to fusible link seems OK, suspect fusible link to MPI harness

That's all I got. If I can't sort this I really might part it out, I won't drive a car that I'm nervous will go down in flames. For now I just want to drive it home, I'm thinking about running a new +12V line for pin10 which I suspect is the short, just to limp home. and thanks by the way, shitty situation but great to have peeps to toss it around with.

 

[mikus]

combined to original post

 

[mikus]

ECU pics...

 

[toybreaker]

p.m. me your phone number, and I'll walk you thru a few things to check.

 

[mikus]

^ this guy is awesome. Grounding concerns on MPI relay were mainly misinterpretation/user error /ubbthreads/images/graemlins/blush.gif I'll write up detailed troubleshooting/checks done, but for now...

Here's some pics of the MPI damage, pin10 meltdown.






I unhooked everything powered by MPI side of relay and tested pin 4,5,or 10 - none show ground. Good

Rewiring of Supra fuel pump looks sketchy in trunk. Power input 12V is on #87 and the wire pulled right out of crimp connector. #30 output looks bad/oxidized. Relay unit is cheap and suspected to have no quenching/suppression diode.




hopefully replacing MPI relay, replacing harness & damaged wire, then cleaning up the fuel pump rewire situation, will resolve the matter.