71 911 stalling issues

[missoula911]

Just wondering if anyone has any ideas on a problem I am having. I have a 71 911E and have been having a stalling problem with it. It first happened a year ago. The problem has always happened after I have driven the car and make a stop somewhere. It does not always happen but seems to becoming more frequent in nature. A year ago it happened after stopping for a while. I got in the car and it started and ran for about a block of so and stalled. After waiting a while it started again and drove home. I changed the fuel filter and it did not happen again for more than 1000 miles. Lately it has happened much more often. Always the same circumstances. I will stop somewhere and come back out to the car and have this issue. It happens when I leave the car for a couple of hours and the last time it happened I was in a store no more than 5 minutes. I have checked the connections seemingly having to do with the electrical system, cleaned the grounds, changed the fuel pump etc. It acts like an electrical issue as the car just dies abruptly. But the weird thing is that generally the car will start right away. It may die again multiple time but eventually I will start it and it will be just fine all the way home. And it seems like when it is running it is fine. Only happens after you stop and restart the car at least to date. There seems to be plenty of fuel pressure at the filter but not sure about spark when this happens as it does not stay inoperative long enough to check because it will start right away. Any ideas would be a help. I am very frustrated at this point. Please let me know your thoughts.

[pors1968]

71E stock MFI or carb

[Porboynz]

Sounds like ignition, but its going to be hard to prove without swapping out things like the coil and CD.

[Flieger]

almost was going to say vapor lock but it starts fine but then dies, which is the opposite of the normal problem. I have a button on the dash for the cold start squirters which gets around the hot start issues (thermal time switch still warm so no enrichment but engine cold enough to need it).

[BK911]

Screen in fuel tank?
Carry a timing light with you. Next time it happens install the timing light to check for spark.

[missoula911]

The engine has the original MFI components less the cold start. The cold start had an issues a year or so ago and my dad and I removed the cold start for fear of fire. I have changed out the coil with no help. It has a Perma Tune CD box in it and I have been in touch with them several times and will probably send it in for a bench test. At first I thought it was electrical for sure but not sure now since it only seems to happen after the car has been warmed up and is stopped and restarted. I was thinking some kind of vapor lock because of the circumstances in which it happens. However not sure of anything at this point. It has never happened while I've been driving it and it does not occur upon first startup of the day. And since it will generally start up after it stalls even though it may only run for 10 to 20 seconds I am beginning to think it has something to do with fuel. As you can probably tell I am at a loss for what to try next. Bringing a timing light would probably work if it would not start right away again but it does so I have to assume it is getting a spark at least at that point. It is certainly a puzzler for sure. Thank you all for your ideas and information and if anyone has anything else to add I am grateful for the ideas.

[Porboynz]

That's interesting: "it never happens when driving"
Forget coils and Permatune etc, they are more likely to fail under load not idle so we need to focus on the idle situation.
I would test your fuel cutoff relay speed switch (also known as an RPM transducer) to make sure it is operating correctly. With the engine running, lift the revs to about 2000RPM then manually operate the micro switch. The engine should die until the revs drop to about 1300rpm then the engine should fire up again, the revs will increase and then its dies again, and repeats.
If the speed switch is misbehaving and not releasing the fuel cutoff solenoid when the revs drop below 1300rpm then imagine what will happen if the throttle does not return fully to operate the micro switch. The engine would die, then after you pump the throttle and restart everything is normal again. You can easily disconnect the wire on the fuel cutoff solenoid to prove its not a factor, expect a few over run back fires though. Its worth checking IMO.

[Porboynz]

Make sure the engine is hot, same situation as when you experience the problem in case its a heat sensitive issue.

[tobluforu]

Permatune, hmmmmm
Rpm transducer, unplug it and see if that fixes it.
How are all of the fuel line?

[missoula911]

Thank you for the additional information. I will check RPM transducer after I can figure out what it is, and see if that is the issue for sure. It would be nice if it were something that simple or I guess I am assuming it is something simple. I think it is something to do with fuel as well. For the longest time it felt like it was electrical for sure but the more it happens and the circumstances when it occurs is starting to tell me that it is fuel related. It may and must have something to do with heat since it has never acted up when I first start it in the morning. The car is giving me clues but there are still many possibilities to work through. The car runs so strong under driving conditions it is hard to have a problem like this happening. But I guess I am expecting perfection out of a 45 year old car and that isn't likely all the time. Thanks again all you posters.

[Porboynz]

The RPM transducer is in a metal can on the engine bay fuse/relay panel. You do not need to identify it just yet, try the RPM test operating the throttle stop micro switch or pull the wire connector off the fuel shutoff solenoid. At least you can eliminate another possibility.