Tonight I was getting the no-crank symptom, now with video. This was after driving about 30 minutes and running into a store for 2 minutes. As you can see, all accessories are powering up, lights and radio turns on, antenna extends, etc. But no crank.
https://youtu.be/3sN9Z2MQ87k

Starting to think multiple issues going on, unsure if they're related. It won't hurt to go through all the connection points and clean them, and I'll do that. I replaced the tranny ground strap and sounded down the areas for it with a steel brush already, but looks like I have a bunch to go through.

Very basic test: turn on thee headlights while trying to start it hot. Do the headlights dim significantly when the key is turned to Start?

Starter or ignition switch or both?
 

I just got through the same type of dilemma you have with start issues , but on my ‘84 3.2. My problem turned out to be a bad ignition switch, the mechanical portion.

I figured this out after installing a hi torque starter which was probably money well spent anyway, cleaning all my contacts, and many hours with a multimeter.

Ultimately I removed the ignition switch and disconnected the electrical switch from the mechanical assembly. This allows you to use a screw driver to start the car and bypass the key/tumbler/mechanical switch . Mine fires up every time now if I just use a screwdriver (not my long term solution)

I would suggest checking that, it seems to be a common problemand won’t cost you anything but time and a sore back.

-Anthony





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Unsure, will try to replicate that condition. I don't consistently get the no-crank. Sometimes it'll crank every time (but not necessarily fire, issue originally posted about). Then I'll have a stop where I have to turn to start a dozen times of more.

I just went out and it cranked and started immediately. Because of course, haha.

Just like what I said previously and similar to what Anthony said, check your ignition switch.

If you can, try jumping the wires (as if you are stealing it) to see if the starter cranks the engine. This route is free and nothing to lose.

Check your new starter positive cable connection is still tight, as well as the 2 yellow solenoid wires.
Also check the positive battery clamp isn’t cracked.
Did you ever check the rear fuse panel 14 pin connector for corrosion on terminal 1?

and again Try changing the ground cable.

Lorne m.

I hesitate to say this is defeated, but the not firing when cranking seems to be defeated. My fuel pump check valve came the same day as my gauges, decided 'what the hell?' and replaced it. No hesitation while the engine cranks now.

Every once in a while it just won't even crank when I turn the key, so now I'm gonna go after all the electrical connections. I know the ones at the starter are good, as I just cleaned those up. I cleaned up the ground strap on the tranny to the chassis, but will just replace it. The one to the battery looks fine, but I'll go after it. Any other obvious grounds to look at?

Long overdue bump, still having the intermittent no crank and it's driving me crazy, as seen in this video.
https://youtu.be/3sN9Z2MQ87k

Running a high torque starter, new ground strap, new battery, new battery cables, new ignition switch (electric portion). CIS removed and now EFI, so my hot start issues are gone, now it's just this. Only thing I can think of is it's the mechanical portion of the ignition switch. Any other ideas?

When you turn the key to start can you hear the fuel pump running?

Take your old ignition switch electrical portion. Plug it directly into the bulkhead. Use a screwdriver to start it. That should identify if its the mechanical portion or not - assuming the old electrical portion is half-way good.

I can't hear your solenoid click, otherwise I'd say to check voltage drop at the yellow wire on the solenoid and work back through every connection. 14-pin plug in the engine bay can get pretty horrid.

Yep, pumps runs every time.

14 pin was eliminated when I did the EFI, so all the wiring back there is essentially brand new. There is very little of the stock wiring in the back at all, the yellow wire to the starter is about it.

I’ll give the screwdriver thing a shot, thanks!

That suggests the ignition switch is OK because the yellow wire is getting power to the pump and should also be getting power to terminal 50 on the solenoid. This looks like a solenoid problem; I just fixed the solenoid on my 1978SC see:

http://forums.pelicanparts.com/porsche-911-technical-forum/1067660-reason-hot-start-problems.html

So I had this problem with my old starter and now also a high-torque starter. I guess it’s possible I had 2 bad solenoids, but hesitant to go down that road. Maybe I’ll run a fresh wire directly to the starter from the ignition and see if maybe the yellow wire is deteriorated somewhere. The connection at the starter is fresh, but maybe it’s somewhere along the run?

There is no substitute for measuring the voltage at the solenoid terminal. A volt or two drop from what you measure across the battery terminals isn't ideal - but not huge cause for concern either.

But if you're seeing nothing - or more drop than that - then you have something to work on.

Have you checked that you are getting 12v on the yellow wire at the solenoid end when the key is turned to start? Not easily done unless you have an assistant to turn the key. My starter is 42 years old and working really well with its new solenoid.