Very rough idle/Accelerating after DME harness cut..

[86 911 Targa]

^^^^^
Fuse panel wiring for our M/Y 86.

Best,

Gerry

[Mony]

Thank you dear sir^


So I identified my 5 wires that were damaged in the process:

1- Black/violet: Tachometer wires
2- Black: Tachometer wires
^ Fixed and tach came back working

3- Full Red: This is my problem! This red wire feeds from the battery and gets into three locations:
- DME Relay
- Fuel injectors
- "Idle Speed Positioner"
then goes into DME. So either I damaged my idle speed positioner, or my injectors or my dme ecu.


4- Full Black: Anti-theft system
5- Red/green stripe: Goes to fuse box number 3 then to fuel pump.

But I tested my idle valve and it gave good readings, also the switch is clicking. If I had problems with my idles would it effect the rest of the driving? I am experiencing bucking and hesitation at all speeds and gears. Car is running and starting, does that mean fuel injectors are also fine? Could it be possible that one or two injectors got burned and the rest are wokring?

Last thing would the DME.. I have no access to any DME near. The only way I would get one is either fix mine or buy another one. Can I test the inside of my DME?

So numbers of wires from top to bottom:

3

[Mony]

Originally Posted by Jeff Burger

did you check to make sure none of the pins in the motronic control unit and connector did not get damaged by the same tech?

Yes all pins are clean and tidy

[ischmitz]

Originally Posted by Mony

So I identified my 5 wires that were damaged in the process:

1- Black/violet: Tachometer wires - engine speed
2- Black: Tachometer wires - fuel pulse duration
^ Fixed and tach came back working

3- Full Red: This is my problem! This red wire feeds from the battery and gets into three locations:
- DME Relay
- Fuel injectors
- "Idle Speed Positioner"
then goes into DME. So either I damaged my idle speed positioner, or my injectors or my dme ecu.

As mentioned earlier the black wire (fuel pulse duration) to the tachometer touching the red wire is what most likely damaged your DME. This would cause rough running with the mixture being off.

But I tested my idle valve and it gave good readings, also the switch is clicking. If I had problems with my idles would it effect the rest of the driving? I am experiencing bucking and hesitation at all speeds and gears. Car is running and starting, does that mean fuel injectors are also fine? Could it be possible that one or two injectors got burned and the rest are wokring?

The ICV vibrating is good and tells us there is no issue. And the ICV is won't affect open throttle. It really only makes an impact during idle. If an injector was bad (open) you would have a cold exhaust port. Easy enough to test. If one injector was short all would stop working. Both is unlikely as no wire involving the injectors was involved in your incident.

Originally Posted by Mony

Last thing would the DME.. I have no access to any DME near. The only way I would get one is either fix mine or buy another one. Can I test the inside of my DME?

There are lots of other 3.2 in the SoCal area, maybe someone is up for a quick swap test. Never hurts to ask. Buying a new or replacement DME is sheer overkill as yours can be tested and repaired. That would be the next logical step. Testing your DME requires an oscilloscope to verify the peak&hold pattern is in spec.

Cheers,
Ingo

[3rd_gear_Ted]

The wires that were drilled appear to be the wires @ coordinates F / 47 on the 1st sheet of the schematic ( the two big red wires) . Looks like the 12 vdc source.

My $.02 of worth thinks, when the drill bit provided a ground path, the DC voltage lowered, the DC amps went WAY up and any components downstream were severely thermally stressed. The rest of the system saw an instant voltage spike that wasn't good either.

All of this in a couple milliseconds

[Mony]

Thanks for all the help guys, %80 that my ECU is damaged. I will have to test with another car first. then most probably send me for a fix.

Thanks again for all who has helped. The Targa says hi.

[mysocal911]

You might try and contact this forum member. He's helped members in situations like yours before.

[86 911 Targa]

^^^^^
Here is the complete sheet #3 from the factory manual.

You will need to cut/overlap & paste.

Good luck,

Gerry

[mysocal911]

Originally Posted by mysocal911

You might try and contact this forum member. He's helped members in situations like yours before.

He has met with forum members and used his car to test DMEs in his car.