1985 911 starting question (spark)
 

I have a 1985 911 that is not starting. I checked for spark and did not detect any. Then a funny thing happened. As I went to shut the key off it sparked for an instant. It has since done it several more times. But mostly no spark. I replaced the dme that was all corroded. I am wondering about the ecu. Could that cause this issue? Is there any way to test the ecu? There is 12 volts at the coil. Ideas?

I don't know where you are located, but the easiest way is to find someone local and see if they can test your ECU in their car. Other wise I'm sure there are places that can test and repair Motronic computers, but I would need to go back and dig up that info.

I would first run some continuity tests on the Crank Speed and Reference sensors. these two sensors are identical, so the easies approach is to just to compare the pin to pin resistance values between the two, as it is unlikely that they both would have failed simultaneously.

Read here; http://forums.pelicanparts.com/porsche-911-technical-forum/621262-911-3-2-no-start-troubleshooting.html

Opening the ECU is pretty easy. If you open it and see much corrosion it is indicating it got wet at some point. Usually a cracked solder joint is an issue. If you have the right equipment, and great eyes, you can fix it. Otherwise send it to one of the guys on Pelican, just do a search.

If you are a PCA member you may find a guy in your region that will try your ECU in his good running car. Don't put his good ECU in your car, if the car has a problem it can damage the ECU.