Please Help! 82 SC Engine cuts out on Highway!

[jrolstin]

Please help... I am trying to diagnose my problem and havn't had time to look at the manual yet to start troubleshooting, was hoping I could get pointed in the right direction.

My SC will randomly cut out (loss of ignition, has to be electrical because the symptom is binary) when driving at highway speeds.

It has only happened a few times. Today I drove 1.5hrs, no problem. On the way home it cut out 5 times... It has happened a couple of times before, at first it would cut out, I would pump the accelerator intermittantly and it would come alive after about 5 seconds. Just today it would not come back on its own. I had to clutch, let it die, and then start it again. After starting it again and continuing on it would cut out again shortly afterwards.

It happened a total of 5 times on the drive home.

Any ideas? Thermal/Electrical problem?

Please help!!!

[Justin@Athens]

Bad grounds? Check the battery terminals, maybe the transmission strap? This is my first inclination on all vehicle trouble now lol.

[jrolstin]

Terminals are fine... where is the tranny ground strap? Picture?

[Justin@Athens]

no pic, but do a search. easy to get to and remove/replace with floor jack.

[edgemar]

fuel pump relay going bad?...had this happen on my 82 it would just die no sputtering and would start up a few minutes later. Try replacing the red relay with a black one next to it temporarily to test if it starts right away. I did that right after it died and it started right up and never had a problem again after replacing the Fuel pump relay.

[jrolstin]

I don't have a problem getting it started right back up, it's just it used to go in and out on it's own with me actually having to re start it.

[chamilun]

check the coil and MSD box if youve got one

[911scVT]

FWIW- I had the same issue with my 82 911 SC and like the other person said it was the fuel pump relay. For me, it had become loose with all the rough roads so sometimes it lost contact and stalled out the car. I firmly plugged it place and haven't had that issue in years.

[carson911s]

In my case - same symptoms and it was the coil. Later realised the box was faulty and slowly cooking the coil.

[fred cook]

Check the fuel pump relay fuse. They tend to heat up more than the other fuses which causes the ends of the fuse to oxidize/corrode. Put in a new fuse, clean the contacts and make certain there is a proper amount of spring pressure on the fuse. Also, loosen the screws holding the wires to the fuse holder on each side and clean the corrosion off of the wires. A .22 brass bore brush will do a good job cleaning out the connector points. Good luck!

[RoninLB]

Originally Posted by jrolstin

I don't have a problem getting it started right back up,

when my coil/CD box was going bad I had to wait for it to cool before it would restart

[jrolstin]

Thanks for all the help so far guys. I've got a couple hours right now I'm going to try and to check out what has been mentioned... How would I diagnose a bad coil/CD box if it is the culprit?

[GothingNC]

Do you have a Permatune box?

[jrolstin]

I'm not sure... still learning. I just got the SC about a month ago and only got a manual about 2 days ago. It's a PDF version and hard to read...

[jrolstin]

I had a look at the fuse for the Fuel Pump...




It might also be worth mentioning in this thread that my fuel pump does not shut off when the key is in the on position. It just runs continuously.

[jrolstin]

I removed what I thought was the fuel pump relay while the key was in the on position and the pump was running. The pump just continued to run. Is this correct?

[jrolstin]

Ok a couple other things I have noticed... there is a switch on the throttle which has no leads going to it... not sure what that is for...



And there is a sensor on the left chain cover which has a disconnected lead hanging beside it...

[speedy]

the top picture is of the micro switch.... you should have a green and brown wire attached and the bottom pic is the thermotime? switch you should have a yellow and a red wire attached. the fuel pump runs and runs because there is a switch on back of the the mixture control unit that is unplugged or not working. it is a safety thing so if the engine is not running it cuts power to the fuel pump(in case of an accident) it sounds like fuel pump, relay or wiring. start it up and poke and shake some of the wiring aroung relay could be as simple as a loose wire.

[al lkosmal]

Pelican Parts - Porsche 911 Parts Listings & Diagrams

Jonathon, the link above will take you to the electrical diagrams for your 82SC. These will help you to sort out your wiring....which appears to have been "modified" a bit.

Your fuel pump should not run in the on position....if it is the same as my 77 CIS system, there is an airflow switch located at the front of the air intake, that is actuated when the air-flow flapper is raised. This, in turn provides power to energize the fuel pump relay. (the air-flow flapper will raise up as soon as your engine starts turning over creating air flow.

I'm not familiar with the microswitch located by the throttle.

The third pic shows the thermo-time switch with its connections flapping in the breeze. The thremo-time switch will energize the cold start injector depending on the temperature. The cold start injector is located at the lower, front of the throttle body and injects fuel, directly into the intake to provide a cold start mixture.
Note: the flag terminals for the thermo-time switch are two different sizes....so it will be easy to figure out which connection goes where on the switch.

I hope that this helps

[jrolstin]

Where do the wires for the microswitch come from? and what is its function? Also what is the polarity of the thermotime?

I pull the most rearward relay and the pump stops running, but there is still a high pitched noise. I plug it back in and it runs again.