1977 2.7 CIS - No spark on crank, spark on run
 

Trying to track down an issue on my '77 911. Car was running and driving when I bought it but has been sitting for about a year.

The car has no spark when cranking but does have spark with the key in the run position. Verified by pulling a plug lead to see the spark. When we're cranking, there is no spark at all. But when we stop cranking there is brief spark as the car briefly turns over before stopping with the key in the run position.

Seems like I've read about this issue before. Anyone have any ideas for me?

Could be low or no voltage getting to the CDI during cranking, maybe even a low battery.

Battery fully charged and tested with a second battery.

You should have power going to the center pin on the CDI .if it's a Bosch 3 pin

Car has a blue Permatune which I believe to be factory (little known fact, Porsche installed Permatune units at the factory on some cars in the 70's). Still a three wire connection. I'll check the power at crank tomorrow.

Any other ideas?

Have you checked the coil?What kind of coil do you have?

Bosch coil. Assuming coil is good as I have spark with key in the run position.

maninblack,

When you are running the starter, there is a separate path for +12v to power the ignition. It is the yellow wire attached to the starter. Could yours be unplugged? It also powers the Thermo Time Switch and the Cold Start Valve.

Got it guys. Break in a wire from battery. Thanks for the help.

Excellent, glad it worked out for you- which cable?