Ignition cranking, but not firing. Would this be the problem?
 

Hi Everyone,

I'm new to the Porsche Community, just picked up a 1981 911sc, and had a great drive up the country (New Zealand) after picking it up. Over 1,200 km and no issues. Parked in the driveway and haven’t managed to start since. It cranks, but doesn't fire.

My working theory is the aftermarket immobiliser has failed which has circuit broken a key component. In my full review of everything, I saw this yellow wire in the engine bay has come loose; any idea what this does?

http://forums.pelicanparts.com/uploa...1619322151.jpg
http://forums.pelicanparts.com/uploa...1619322151.jpg

Thermo time switch for cold start injector.
It tells the cold start injector on the rear of the air box below the throttle body to squirt gas into the intake on startup.
You should repair it. A .250 female 90 degree connector is what is needed to reconnect it to the round brass terminal on the switch. Just slide the old one off. In a light a straight connector could be used.

Thanks, would that prevent the car from firing on cold start? Trying to work out if this would stop the car turning on, or if that's just another issue running parallel to the car not starting. I've got the alarm specialist coming out tomorrow morning to bypass the alarm/immobiliser to see if it fires, but thought I would check this first to save a call out fee.

See my edits. Better fuel control at cold start is likely what it needs.
You could try giving it some gas at the throttle while cranking to see if it will start. (More air will flow)

I would also try 'start ya bastard' or brake cleaner in the intake to see if it fires up to see if its fuel or ignition related

Took the connector off, rewired the yellow cable in, and wound over. Took a long time to fire, and was very lumpy for about 20 seconds, but idle settled down and ran fine.

Went for a 20 minute drive and ran fine. Turned off, and back on and started first pop. I wonder if this coming off, plus me continually trying to start it for the last 24 hours is what caused the slightly lumpy idle on first run.

Good job. Cylinders/plugs may have been slightly wet/flooded with fuel.
Taking it for a good drive may have cleaned them up.

Spark plugs........
 

Removed and inspect your spark plugs. Clean them and re-install. That broken yellow wire would cause the TTS NOT to heat up and make the CSV injects fuel every time the starter is energized. Too much unburnt fuel would tend to foul up your spark plugs.

Tony