Is this a vapor lock issue with the CIS?

[Walt Fricke]

I think Tperazzo has aligned the viewpoints - Tony's that air bubbles or whatever in a line eventually to a fuel injector aren't going to prevent the injector from spraying fuel at full pump pressure, and my and others observations about hot start issues with some models, and our speculations as to heat being a cause of hot start problems. Namely, that where this air or whatnot is in the line matters - pre-pump, or after the pump.

As Ed points out, this didn't start out as a hot start issue - it was a "died at a stop light" issue, followed by a hot start issue, followed, after some time, with a restart. I'm inclined to view the location of the fuel pump as the key to all this, but it doesn't necessarily explain why the engine stopped to begin with. Happily, he points to Porsche's instructions. And maybe adjusting the idle a little higher might fend off random engine stops?

Me, I'd make the effort to move the fuel pump back up front, along with the kind of CIS checking and tune up where Tony is so helpful.

[HarryD]

I think there is a basic issue here.

FWIW, I have been driving my 1973.5 for about 20 years. When I have had running/stalling/starting issues looking that these items below seemed to fix the problem:

-Is the car in proper tune?

-Cap, rotor, wires, points all in tip top shape?

-Dwell, timing and idle to factory specs?

-Is the cold start injector connected and functioning?

-Is the mixture ok? Address above first.

[Sunroof]

Lots of responses and great suggestions. The sudden shutdown is intermittent. It has happened two of the last five drives I have taken. The two Porsche shops I called, simply said that they must reproduce the problem in order to fix it! That sort of leaves the shop out of it for now. I can tell if its gas right away after shut down with the key on, and the sensor plate pushed up the injectors get charged by the pump. That one is pretty clear for me. I have had a pump fail before about a decade ago and replaced it. Pierburg and rebuilt Porsche pumps for this car are not that expensive. When I had a coil failure about 15 years ago, the car would not restart well after cool down. No spark! When I had a CDI failure the unit would not "hum" and that was replaced. After owning this car for over 20+ years you kinda get to know its personality. So to answer some questions, the fuel tank was refurbished and the internal filter changed. The injectors are new as well as the dist. cap, rotor, BERU shielded ignition wires, spark plugs, coil, wire harness (CDI to distributor/coil), fuel filter and accumulator. Not much left to list.........The ignition unit is a cheap fix as to the cleaning and replacement of fuse number 7 that controls the fuel pump. Vapor lock is indeed questionable because I have run this car in Georgia summer heat for many summers and the only problem on occasion was "hot start" and that was cured with the Porsche 914 Hot Start kit.
My wife is giving me grief and in a way I am fed up AS WELL. This is my fourth Porsch over the last 48 years. My best friend always asks, "ARE YOU FED UP BEING STRANDED AND TOWED"?
Yes, I am and when I get this problem resolved I am going to sell it!!!
Thanks for the input everyone.
Bob

[HarryD]

A sudden shutdown is typically a failing electric component. When it fails immediately see what is warm to the touch (CDI or Coil). Cool with ice or cooling spray. See if it restarts.

[E Sully]

Owning a 49 year old classic car is never simple. It's an individual thing if it's worth the hassle. When I want simple I have a 2005 Toyota Corolla. My friend uses his 1964 356 daily when the roads are clean. Occasional towing and my roadside assistance happen a few times a year. Haggerty has always been good to him with towing. I have replaced his fuel pump twice, points and condenser, Zeniths with Webers and adjusting mixture and idle, fixed minor electrical issues, and assorted other problems. Last 2 times it was simple, his gas gauge is not accurate and he was empty, and then the carb linkage popped off.
I'm curious, how was you fuel tank was refurbished? While you mention a lot of tune up parts, have you had the fuel pressures checked? Is there electrical power to the WUR and is it operating properly. There is one round black relay in the rear panel that operates it.
Like I said earlier, one of the first things I do when there are problems is pull the spark plugs. This can give an easy way to see what is going on in the engine. Are the plugs clean, or fouled by oil or gas. A compression test to see if the rings, valves and are ok.
You seem to have a misunderstanding of fuse 7. Fuse 7 only protects the fresh air fan. When ignition is on, direct battery power flows on the Rd/Bk from the ignition switch terminal 15 to the line side of fuses 7 and 8, which have a strap in the fuse block connecting them. The fuel pump, CDI unit, and gauge power wiring on this side of the fuse block have no fuse protection.
I do wonder if all the terminals and terminations in the wiring harness are good. Have you checked the pins in the connectors? While you have installed new distributor parts, is the distributor itself good? Mine was worn and I refurbished the advance mechanism and eliminated shaft play.

[eastbay]

Another tip is to go to your fuse box and snug all the screws, especially the fuel pump wire. I have never found a 911 where there were not any loose ones. Can fix lots of naggling electrical issues.

For an example of potential issues, take a look at this thread:

Fuse Block hidden problem