72 dies when key is released

[narley]

My '72 911 attempts to start when I turn the key but then dies as soon as I release the key. Start circuit is working but the run circuit isn't? Any ideas would be appreciated!

[ossiblue]

I'm not too familiar with a 72 but I believe there is a relay of some sort for either the fuel pump or a cold start injector, that is not found on other early CIS cars (yours is MFI)--someone with direct knowledge should respond soon--and this may be bad. It does sound like a possible fuel pump problem in that the pump may not be working in the "run" position of the key.

[Grady Clay]

narley,

Welcome to the Forum.
You will find a lot of help here.

I assume you have a relatively standard ’72 911. It doesn’t matter if it is a 911T, E or S for this purpose.

The most suspect is the electrical half of the ignition switch.
Turn the key to “ON”. See if the CDI box is making a ‘singing’ noise.
If not, run a power wire from the fuse to the single connector on the ignition wiring harness (single red wire and 1-pin connector). The CDI should ‘sing’.

You should also try keeping the key in different positions after you let it return from the “START” position to the “ON” position. See if it is ‘positional sensitive’ to continue running.

The electrical part of the ignition switch is relatively independent of the ley/lock/steering lock part. If you look under the dash you will see the large cylindrical socket that is part of the wiring harness. Next toward the dash (toward the rear of the car) is the electrical switch (Porsche part number 911.613.017.00). The switch has male pins thar contact the harness socket. The switch is a separate part but is bolted to the lock assembly from the driver’s side of the dash.

Occasionally there is poor electrical contact between the switch and the socket. You can pull the socket off the switch and inspect the connections. While there, look for any loose or discolored contact pins on the switch – an indication of an internal problem.

We can lead you through the process of replacing the switch if necessary. It is also sometimes possible to disassemble the switch and repair it.

Best,
Grady

PS: Go to your ‘Signature Page’ and add your location, name and car model. Pelican ossiblue L.J. in Capistrano Beach is a good example. This way you may find some local helpers.