911SC stalling while driving
 

My first post.
At my wits end. I’ve scoured all of the internet for answers. Seems that other people have had similar issues but their remedy’s aren’t curing mine.

My US 1978 911sc will be driving along fine and then will die. Not all electronics go, just the engine will stop producing spark. I’ll coast to the shoulder or an exit ramp and sit. The engine will sometimes restart immediately and sometimes it will crank and crank and not start. I notice that unless I either wait a certain amount of time or I unplug the 6 pin then plug it back in It will start. This last time it didn’t seem work but I carry a spare permatune gen 3. I’d unplug the one in the car and just plop the replacement in and the car will slowly sputter and idle normally. This will allow me to nurse the car back but will sometimes stall on me again and leave me on the shoulder. Then I plug in the original and I’ll continue driving and still stall occasionally on my merry way.
I have a new battery, cleaned all the grounds and had my distributor rebuilt recently by partsklassic and I’ve replaced power harness. Brand new green wire.

One year prior to this issue I’ve replaced the alternator and the external Voltage regulator.

I’ve checked Fp relay, pressures. Etc. I don’t believe it a fuel issue. All fuses and connections checked.

I have two gen 3 permatunes , a black bosch coil and a brand new Msd blaster high vib coil. All combinations of these components will exhibit the same symptoms. I find it unlikely that every single one of these components are failing in the exact same ways.

One thing I haven’t checked is the RPM limiter switch behind the fuel gauge. I’ve read unplugging that it fixed at least one person’s intermittent running issue..

Any help is appreciated.

Since the external ignition parts seem to work and display the same symptoms, I would take a close look at the distributor. Loose or internally broken wire to the CDI box, distributor pickup, bad grounds, etc.

The problem source is explained here; https://rennlist.com/forums/911-forum/1338680-911sc-dies-while-driving.html

Both your permatunes COULD be bad, it sounds like you think they are fine though. The best option would obviously be a Bosch 6 pin cdi box but all of us here know about the $$$ I would go on ashlocks site though just to see what one would cost you.
Assuming your current cd box is good though I would be hooking up a scope to the power supply to not only see the voltage but any funny business. There have been cases like this where the power supply drops out for a second and you won’t be able to see it with a meter you have to look at the waveform. I would also hook the scope to the green trigger wire going into the box and confirm the waveform looks good.

NeunelferPNW: Be sure to put your location in your profile. I live in Woodland WA. If you are nearby you can borrow a good CDI box from me for testing.

Will do so! I was just in castle rock last week. I’ll keep that in mind. Thank you

That sounds like what mine did when the "green wire" was going out. Go start your car, then give the wire a wiggle near the distributor- does that kill it?

The cause of my green wire failure was a bad voltage regulator, so if your green wire fails, check the alternator's output voltage.

This was my initial thought. I have a brand new bosch wire.

Bummer. And a new voltage regulator. Probably still worth verifying the voltage it’s putting off, and the quality of the grounds at the alternator.

Next, you might be right with the rev limiter. These early SCs are pretty simple though, not a lot that’d kill it in that scenario

I’m going to try replacing the pick up coil and the ground with a brand new one. What’s the proper pulse VAC when cranking?

Hello there:

If your car is CIS, what type of gasoline are you using? High ethanol will cause issues such as this during the "raining season" in the PNW. Seems like an odd thing to say, but have you ruled out water in the gas tank?

The other issue may be with the fuel accumulator...just a thought.

Hope this helps. Good luckSmileWavy

Fuel was my first suspect. I bought the legitimate gauges and spent hours on the system, testing. Referring to charts and graphs and swearing. I do know about the hot start issues people have with the accumulator but after a few trips where I didn’t have any stalling issues, hotstarts weren’t an issue.

I’m very sure this is an electrical issue. Seems to be happening after the car is warm. And the short term remedy is unplugging the CDI and plugging it back in. Plugging in a different one which will work for a few miles, or waiting. I’ve cleaned the grounds but they’re probably original to the car and I can easily bend the ends with my fingers.

I run the ethanol-contaminated crap in my car all the time and it runs fine, but I do use my car regularly and put at least a full tank of fuel through it every month, usually every week. It's not the gas.

In the first thought i was on the green wire as well. You wrote that it is new/replaced. But are you sure that it is working properly? The problems you describe fit very well to a failing green wire.

Nevertheless - I'm with you that it seems to be an electrical problem, even as written with the green wire. To me it sounds as well that it could a thermical problem. Get some ice spray, make a test ride, if the problem occur cool down the permatune box with the ice spray and try to restart. Check both ignition boxes you have. If it starts right away and runs after cooling it down go back to your garage and make a cross check with a heat gun: Try to start the cold engine, heat up the ignition box with the heat gun - when it stalls, voilà! Make the tests more than once to be sure.

Thomas

If I’m paying 100 dollars for a bosch little green wire, it better work right out of the bag 😡. I shouldn’t have to buy a new one. I get no indication of it failing with a multimeter when I shake it or twist it.

I got that you're in anger. I'm also in anger according to these prices for a tiny bit of copper, plastic insulation and a plastic plug. But I experience also a lot of bad quality on parts more and more in the last years. Unfortunately you cannot rely on new parts as we did 10 years before...the quality goes down more and more.

Thomas

Don't waste your time on the green wire!!!! Your failure data is more indicative of bad Permatunes, most/all the Permatures in the Bosch castings fail as yours have.

I had stalling issue on my 78SC and replaced Ignition Distributor Green Wire with After Market green wire big mistake and then replaced that with Genuine Porsche Part #: (930-602-907-01-OEM) solved issue.

Can someone lend you a cdi box? Pretty sure that will put an end to your March madness. I have a couple but I’m in N.Y. Try to borrow one from somebody asap, this is probably the issue but if not will check one more variable off your list.

John Walker is pretty close to you. I'd probably give him a call. He's who I'd call :).