Again! ‘85 911 not starting!... sometimes!!!!
 

After 5 months of trying to figure it out, and I thought we did, the car is not starting periodically.

New Starter
New battery
Getting a click noise when the key is turned.
It’s doesn’t start! well, sometimes it does and sometimes it’s doesn’t !!!
No rhyme or reason.

Help!!

I had the same problem..try and wiggle the terminal wires..that where I found the issue in mine...good luck

Starter cable, battery cables, or ground strap. Put a jumper cable from the positive battery terminal to the hot side of the starter and see if it works when you’re getting clicks and eliminate everything in between. If it still clicks then it’s a ground problem between the starter and the battery. Usually the ground strap.
Tony

Thanks Len 911
Thanks Tony
For months I trIED all the above and found it was, or thought it was, a faulty battery... I replaced it and now it’s doing it again.
I will start over and take the advise you both gave me.

How old is your voltage regulator?
Does your battery get hot and start to gurgle?
Are there sporadic spikes in your tachometer gauge?
Does your battery read above or below 12.5 VDC at idle?
Might need a new generator/voltage regulator; they go out slowly.

Remove the positive clamp and recrimp it to the cable with some big visegrips. Seen several lately with a poor contact issue and symptoms like yours.

Had the same problem. I rebuilt my starter and eventually had the same problem again.
A new high torque starter fixed it.

JG... one click or constant clicking?

Same issue on my ‘82 SC, the inexpensive and lightweight high torque starter cured my intermittent start issues as well. A relatively new Bosch rebuilt starter was the problem (heavy sucker too). My ground wire was in good shape and tight.

I thought it was the ignition switch, PITA to remove (and no cure).

Discseven
One click

Tach is spiking
 

Yes, I do get spikes on my tachometer! That has been going on for a while..periodically
I would have to tap gas it to bring it to normal idle
what does that mean?
everything else seems normal.
I was leaning toward a Ground Strap and battery cable ground

thanks

Does this occur when the engine is both hot or cold? Was your replacement starter a Bosch reconditioned unit. Heard of some issues with these but not related to a non-start like you are experiencing.

When hot
 

Definitely when hot.. Know it happens when driving around for a while...don’t recall if it happens when cold... don’t think so

I had similar issues with mine, new battery, new starter motor etc, would start when cold, get about a mile or so, switch it off to put fuel in, go to start it, just a click!
It turned out to be the earth strap off the engine to the body [under right hand rear as your looking from the rear] it was tight, but when i removed it, it was coroded between the body and the strap, cleaned everything up, put plenty of copper slip on the fixing bolt at the body, tightend everything up, no problems since.
Hope this helps.
A...

I had this issue when the engine was hot also, finally replaced the starter with a hi-torque unit and problem never reappeared. Research "Heat Soak", not sure why this would happen with a new starter but then again...

edit: If you don't want to replace the starter again you could try this relay kit. Note I don't have any direct experience with it.

http://forums.pelicanparts.com/porsche-911-technical-forum/602587-what-does-hot-start-relay-do.html

Sounds like what was happening to my '88 a few years ago. Would fail to start about 20% of the time. One click only. New ground strap fixed it 100%. $10 fix... try this first.

Missed you didn't clean your ground straps. Start there for sure.

I spent a couple months with the same issue.
Cleaned the already clean ground straps.
Cleaned the already clean battery cables.
Replaced the still good battery.

The spiking tach is just about a tell-tale sign that your voltage reg is on its way out.
I learned they fail slowly, so this is a sign.

It ended up being the original (read 42 years old) voltage regulator.
The thing was so worn down, it was overcharging the battery and making everything just seem like an electrical nightmare.
But, just replaced the voltage regulator and generator with a reman unit from Pelican and all the problems went away.

As always, your results may vary, and I'm not a mechanic.
Good luck, cheers.