I am experiencing intermittent problems starting my 78 911 SC.

There doesn’t seem to be any rhyme or reason, I was away for a work trip for a week, came back and the car wouldn’t start, I tried again the next day and it started on the first try.

Parked the car for 2 hrs after an hour long trip and it wouldn’t start, started fine the next day.

Just drove car to gym where I worked out for 2 hours, came out and car wouldn’t start, turned key several time and it suddenly cranked over.

I can hear the fuel pump going every time when I turn the key, but the starter does not crank the engine over.

I’ve had the car in the shop twice to try to resolve this problem, the starter was replaced the first time and the battery was replaced the second.

Has anyone experienced this issue before? I suspect a possible cause is the ignition switch? Any was to test and know for sure?

Car is a 78 911 SC with ~210k on the engine, the top end was rebuild about 60k ago.

Thanks in advance for any and all help.

How old is the ignition switch?

My brother had a similar problem with his 84 Carrera, he replaced the electrical portion of the ignition switch.

John

Sounds like the ignition switch to me. With an intermitent problem you can only really test before and after. find the ignition or starter line coming from the ignition switch , hang a volmeter on it and see if you are getting power when it is working ( you obviously will ) . So now you have a set of PArameters to go by when it is working.
Throw the meter in the car and wait. When it fails to start get out your meter and your notes. and now compare to a car that is not working ,,,,, this is the only way with an intermitent problem ...

.. or you could buy the electrical part and throw it in ... see if it fixes it ....

Prepare to have fun accessing the bolt on the left lower dash knee pad for access, unless you are a flexible Yoga expert.

Electrical portion of the switch is cheap, the mechanical key lock assembly drains the wallet.

Nice long thread on the replacement.

http://forums.pelicanparts.com/showt...ch+replacement

John

As far as I know, the ignition switch is original and has never been replaced.

My mechanic did check the voltage going to the starter and found I had a dead cell in my battery the last time the car was in the shop, I'll see if we can replicate the problem again.

hmm. sounds like the problem im having. Is the car starting with a jumper or do you have to kick start it?

The first time this happened, I tired jumping the car with no luck, kick starting does work.

Another data point; Lights and radio all work fine when key is in on position, car just won't crank over..

sounds like the " start" position on ignition switch

Do you mean there might be an issue with a specific position in the ignition switch?

Or it may just be loose. Try to reach up and move it around to see.

yes it is very possible only that one position has a problem. the sprung part moves the key to "start" . I f that part is bad .. no start ..

OK, I just had the electrical part of the ignition switch replaced by The Staple in SF (great shop, BTW), the car started everytime with no problems for a week, then last night, it wouldn't start again...I push started with the clutch and it now starts fine, this problem is killing me...

When I had the car in the shop, they thought the only possible cause was the ignition switch as well...

To recap, I've replaced the starter, the battery and the electric part of the ignition switch, and now I'm stumped, what else can it be? bad wires?

Any help would be greatly appreciated. Thanks in advance.

Check your fuel pump. When was the last time it was replaced? Otherwise check the DME.

When you turn the key to the "start" position, and hold it, do you hear a humming? Anything? When the starter was replaced, was it a new or rebuilt unit by Bosch? Or did you take it in to a shop to be rebuilt? If so, the do you know which parts were replaced?

You should check the connections to the starter and make sure that you use a thick or "primary" wire to be sure that you are getting enough juice to the starter.

When I turn the key, I do hear a humming sound for the fuel pump, sometimes it's quite loud and sometimes not.

The starter was a rebuilt unit from Bosch, I'll need to talk to the shop to find out which parts were replaced. The last time I had it in the shop, they checked the wires to the starter and that's when they discovered I had a weak battery, which was replaced, I suppose I could ask them to check again.