Please Help! 82 SC Engine cuts out on Highway!
 

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!!!

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

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

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

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.

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.

check the coil and MSD box if youve got one

Ditto on Fuel Pump relay.
 

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.

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

Fuse
 

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!

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

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?

Do you have a Permatune box?

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...

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

http://forums.pelicanparts.com/uploa...1310309484.jpg
http://forums.pelicanparts.com/uploa...1310309494.jpg

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.

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?

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...

http://forums.pelicanparts.com/uploa...1310309907.jpg

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

http://forums.pelicanparts.com/uploa...1310310031.jpg

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.

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

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.

Al, great post, thanks for the info... I only have one flag terminal and am still unsure of the polarity. on the thermotime there is a longer terminal and a shorter one. Can you tell me which length is for the positive lead, or red lead?

This will help you out with the mysteries of CIS

CIS Primer for the Porsche 911

you would have to trace the wiring the diagram to answer that question but I do know that its part of the harness that connects to the plug at the firewall of the engine. go to lambda system. the red relay is the fuel pump relay and yes if you pull it the pump should stop the high pitch noise from the enginge bay is the cdi box and you should hear a buzzing noise which is your freg valve

Check the wiring harness that comes out of the back of your ignition, IIRC part of it goes into a plug (similar to the mirror plug) that plugs into the firewall/footwell. Be sure that isn't loose, popped out on two of us racing that I know of, kills the car dead in her tracks..

Ok I cannot find any leads going to the air flow metering sensor that would tell the fuel pump to shut off... where is the connection? I need more help understanding exactly how it is supposed to work... :(

The terminal posts on the thermotime switch are two different sizes...two different diameters, to accept two different size flag terminals. The yellow wire goes the the terminal post with the smaller diameter, the red wire goes to the terminal post with the larger diameter. (closest to you in this pic.) Look at your thermotime closely and you'll see the difference in sizes.

regards,
al



http://forums.pelicanparts.com/uploa...1310324812.jpg

Here is a pic, showing the safety switch connector (blue) on the front side (closest to the front of the car...I.E. hardest for you to reach in the engine compartment) of the air flapper housing. You can reach it by reaching around from the left side of the intake..........or you can remove the top rubber cover that connects the flapper intake to the throttle body and have better access.

http://forums.pelicanparts.com/uploa...1310325267.jpg

PS: you will need to be able to read...and understand wiring diagrams...and have, and be able to use, a multi-meter to be able to debug the wiring in your car........if you are not handy at the reading/interpreting part or the use of a multi-meter.... holler for help and see if you can get somebody local to come out and help you debug. It's a bit confusing to the uninitiated...........and wiring issues are a PITA to chase down.

Al,

I am pretty handy with reading/interpreting electrical diagrams and using a multimeter, should be able to figure it out - just needed to know where to look :)

Thanks a lot. I will try to take a look at this tonight when I get home from work.

As for the Thermo-Time switch... If it is not connected, will it run as if it is in cold start mode all the time? This may be the cause of my performance issue...?

I'll 2nd this question...when my '80 SC had a Permatune box installed, it experienced the same issues as the OP's SC...man, having the engine cut-off on the Golden Gate Bridge is a bummer!

If I recall, the tach would sometimes wildly bounce up/down just before the engine was cutting off or it would sometimes bounce and nothing further occurred...except my rapidly increasing heartbeat...it was stressful and after Permatune replaced the box and it failed again, the SC was fitted with original equipment and all was better.

Good luck with the diagnosis and repair!

@dyusem,

Thanks for the advice. My tach does not do anything abnormal. It reads RPM signal very clearly and does not seem to be malfunctioning. I will have a look at the CDI box tonight to see what type it is.

I am going to go to a partsource tonight and try and get some new flag terminals for the thermo-time switch.

You can set up a mirror and light behind the engine so you can see better back there. look around the area were it should be plugged in.
The connector is part of the engine wiring harness so it should be laying back there some where.

The wires being off of the thermo time switch will not make the car run rich . it only activates the cold start valve when the engine is cold. so as of now your cold start valve is not working.
When the engine is cold it makes the connection between the yellow and red wires to fire the valve. when it is warm it breaks the connection. No need for extra fuel when the engine is warmed up.

Thanks Ron for that clarification. I will have to look elsewhere for my ponies... It still feels like a lot of them have left the stable...

I got my thermo-time switch hooked up, It doesn't start up as quickly cold but it definitely runs better cold. In removing the top rubber cover of the air flapper housing I decided to check full throttle. I realized I was only getting 20 degrees of rotation out of the throttle plate. I got distracted by this, adjusted it and took it for a drive. Massive improvement... I found my loss in power!

So I also looked for a while at where the safety switch is. I felt the connection, wiggled it while on etc, no avail. Connection seems good. However I can't tell how the switch is supposed to actuate? I lifted the flapper and lowered it... I don't see anything resembling a switch... Is a contact thing? I tried bridging where I thought that might be and still nothing... What do you guys think? I need help to understand the type of switch used here... I can't determine it on my own.

Thanks!

bump

holly crap what a small world .... i was just doing some research on a cdi box im trying to repair and did a search and came up with this old thread ...
I was parked next to Jonathon just on the weekend at a BBQ and we were chatting about our SCs, ( he did some nice work on his ) .

Then i read through the thread and see the pic of the back of the CIS is mine :) . its from when i blew the airbox and took some pic for reference coz someeone wanted to see the safety switch ...


too funny ...

Hilarious... I guess to follow up on an old thread... I didn't know what I was doing then, it's all figured out now! - CDI was replaced with MSD 6AL along with a few other tricks... ;)

That is the fuel pump relay. Swap it out with the one next to it and drive it. The rearmost relay should be red. If not, buy one. It has extra goodies inside to protect your elec system.

Also, high pitched noise coming from where?

EDIT: Oh Cripes. I need to look at dates.