ECU cable caught on fire

76carrera3.2 · 03-01-2006, 03:12 PM

My car is a 76 911S with a 1984 Carrera 3.2 conversion. I did the conversion myself in 1986. The engine has completely quit on me twice now in the last month with no warning. Eventually it started but the second time I drove for 30 minutes and it cut off again. As I coasted to a stop I noticed grey smoke coming out of the engine lid vents and smoke also poured into the passenger compartment. After inspecting the suspected areas I found heat damage to the wire bundle going from the ECU under the seat to the engine. Haven't been able to get real deep but a cursory inspection looks like the shorted wires are the ones going to the ground wires on the intake manifold. Any ideas where to start?

Brad01mc · 03-01-2006, 03:50 PM

Hi!

I've had something similar happen to me.

I would un-bundle all the wires and look for the cause/source. Separate all the individual wires because they will have probably melted together.

Usually you can figure out which wire is the culprit, since most of the smoke is going to come from the "bad" wire! In other words, the barest wire is probably the cause. You might also find bubbles, or other melting/deformation of the insulation in other areas of the wiring. Make sure you check the entire length of wire, and not just the place where things burned. This damage can also help determine which wire is the cause.

I would also look to see if you can figure out if the problem was related to pinching, or rubbing.

If rubbing, sometimes the stripe color on the wire is gone, or faded and sometimes there will be groves or "flats" rubbed in the remaining wires.

Pinching will show broken wires and some of the surviving wires will be kinked, or bent/look funny (because inside, the wire is broken).

After that, I would take a look at the wiring diagram and try to figure out what wires "fried" and see what other components might be affected downstream.

Then, depending on why this happened, make sure you either remove sharp bends, or secure the wires so they don't rub against each other. Cross your fingers and hope nothing else fried.

In anycase, I'm happy to hear that you didn't burn it to the ground!!

Good luck!

Brad

ianc · 03-01-2006, 05:57 PM

My guess is something to do with the way you routed the wires from the ECU into the engine room. If you installed a grommet, did it work loose? Check the entry and exit points for wiring to see if it could have rubbed and worn there and look for damaged wiring. At least you'll know the cause. As for the repair...

ianc

76carrera3.2 · 03-01-2006, 06:11 PM

Thanks Brad, I appreciate the response. This car has been with me a long time and I was just sick about it but very thankful no flames were licking up out of the smoke. I did see a bare wire but haven't pulled the harness out of the car yet to trace which one it is.