Ok, so my buddy has an ecu out of a 91 DSM that was in his newest purchase 986/1000.
The guy that he got it from had said it had a remaned ecu that he bought through a local parts store. He took it out to throw into his eclipse, and the car ran fine, until he mounted the case and it grounded out. After that, it ran on 2 cylinders. As soon as he un mounted it, it ran fine again.

I told him to open the case and see if there was any wires or what not on the back of the board from a repair, and sure enough there was. Well it was hitting, but after a little modifying to the case, it cleared. He put it back together, and it did the exact same thing. When its unmounted, it runs fine, as soon as it is grounded, it kills 2 cylinders.
So it dosen't seem to be the issue as far as the clerance in the case, what the hell?

Any thoughts guy?

(Terry, Jeff, are you out there? /ubbthreads/images/graemlins/uhh.gif)

Don't mount it. /ubbthreads/images/graemlins/dunno.gif /ubbthreads/images/graemlins/tongue.gif

Maybe when you push it up in it's spot, it is pinching something.

Thats what he thought of doing, but he is selling the car, and is taking out the e-prom and replacing it with the non eprom which is the one with the issues. The guy that is buying the car is going to use it for racing and not going to mod it anymore than what it is.

With limited information provided I guess it's really difficult to tell what's happening to it

Have you friend, however, tried to use nylon screws + insulting tapes etc to mount the ECU so as to make it not electronically conducting to the chassis (= ground)

The ECU board is already insulated from the ECU's ground plane, so I can't see why it would make any difference, unless mounting is also putting stresses on the board that are opening up a bad connection or something. /ubbthreads/images/graemlins/dunno.gif
If you remove the board, check around each of the 4 mounting screws, top and bottom, and I think you should see that there is no electrical connection whatsoever between the screws and the PC board.

Try and leave it unmounted and twist it around with the car running to put stress on the wiring harness. I would bet that there is a broken wire or loose wire in the harness connectors.

Good suggestion Terry. Actually the case is supposed to ground to the chassis. One of the mounting bolts is even and "E" bolt that is specifically for that purpose.

Quoting Terry Posten:
Try and leave it unmounted and twist it around with the car running to put stress on the wiring harness. I would bet that there is a broken wire or loose wire in the harness connectors.



We went around that scenario as well, and it didn't matter what possision it was in, as long as it never touched a ground to the case, it was fine.


Quote:
keydiver


The ECU board is already insulated from the ECU's ground plane, so I can't see why it would make any difference, unless mounting is also putting stresses on the board that are opening up a bad connection or something.
If you remove the board, check around each of the 4 mounting screws, top and bottom, and I think you should see that there is no electrical connection whatsoever between the screws and the PC board.




I'll take it back out, but I could have sworn that it did make a connection through the case to ground the board out.

I.E. Like iceman said..

v v v v


Quote:
iceman69510


Good suggestion Terry. Actually the case is supposed to ground to the chassis. One of the mounting bolts is even and "E" bolt that is specifically for that purpose.

Well you can get an ecu pinout chart. Then mount the case with the ecu connectors unconnected. Get a multimeter and check for continuity to ground. If its a pin that isn't supposed to have a direct path to ground that's the effed up circuit. Assuming the issue is in the ecu.

Any logger data? It's worth a shot if it's going to isolate which possible wire or contact is causing the drop of cylinders.

Ill check on the schematic when I find it, as for the logger data, no. This is just a stock non eprom ecu that is now going on to the shelf if I cant figure it out. I ended up giving him another 90 non eprom and swapped the pins to get the car sold.