Troubleshooting........
 

Hugh,

You are correct. You need to identify if the problem is FP, ignition, or temperature related. Testing will narrow down the most likely culprit. Be patience and this investigation requires a systematic approach to identifying the root cause of your problem. Sometimes it is right in front of our nose but failed to recognize it.

Make sure the jumper wire terminals @ 87a and 30 connected to the FP relay socket are secured tight to prevent them from coming loose during the test drive. Take your time and keep us posted. Thanks.

Tony

Hugh,
There is a flaw in your theory of if the car quits, then fuel pump will run.
If you lose power in the run position then the fuel pump will stop running.
(Power to 87a comes from switched power)
Checking for 12vdc at both 87a and at the power supply in T2 for the CDI would be a better test.
Fuses 16 and 11 are easy to get to and are where you can measure for switched power for both of the above.
(Count back on fuse panel from the front of the car)
That simple check would tell you if switched power is gone.

I was able to go for a drive today but before I left I connected the ground end of a trouble light to ground so it was readily available to check for voltage at fuses 11 and 16 should the engine quit.
As it turned out the engine did quit after 30 odd miles, so I just coasted to a stop without touching the key. It was in the "run" position.
As I climbed out of the car I could hear the fuel pump running. I must remind you that I was running with the jumper wire in place at the fuel pump socket.

I did check for voltage at pins 11 and 16 and of course there was voltage.

So, having eliminated the fuel pump as the culprit causing my engine to die it looks as though the problem might be the ignition circuit.

Looking at the Bentley manual, page 940-4, it shows voltage to the electronic ignition originates at fuse 11 and works it's way to fuse 22 before continuing on to the electronic ignition. Problem is I only have 21 fuses on my panel so I'm not sure where fuse 22 is. Would that be one of the three fuses in the engine compartment?
How do I go about checking the wiring to the electronic ignition?

Also, the manual shows a "test " connection. Where is it located?

Thx for the help.

Fuse 22 is on the rear fuse panel by the CDI. Physically the CDI receives power from fuse 11 before the wire runs to fuse 22 for other purposes.( That is why there are 2 red wires in T2, one in from fuse 11 and one back out headed to fuse 22).
So it likely isn’t the power supply to the CDI.

My next conclusion (assuming green wire from dizzy is good) would be the CDI unit or the coil for problems.
When it quits, pull the center coil cable from the distributor and test for spark to the engine case very carefully using a helper to crank the engine. Insulate yourself from the coil cable. Very high voltage... I have used a spare spark plug to do this test. Outer Electrode grounded to case of engine.

Alternatively if you have a timing/strobe light, hook it up and test for proper strobe.

My bet is on the CDI unit suffering typical heat failure mode. Quits when warm and works again after cooling off.

Bob Ashlock or Ischmidt (?) can likely help you out for the CDI.

Recent post about 8pin CDI repair has a few names in it for testing/repair services of CDI’s.

We did establish you don’t have the silver Brazilian coil correct?

I have a black coil.
I dont think I have to check for spark after the engine quits because the engine invariably starts immediately each time it quits, so I know there is spark there. And nothing has had time to cool down. Not the CDI nor the coil.
As I may have mentioned earlier, my CDI unit was rebuilt two years ago by B. Ashlock and since the car starts immediately, every time, then the theory of the CDI unit quitting when hot and working when it cool is out the window.
The green wire was replaced two years ago and I have no way of checking it due to the bizarre nature of the problem (the car has not refused to start every time)
So it appears as though there is a faulty wire or connection somewhere that is causing the ignition system to momentarily shut down.
Not an easy one to find, I know, but I'll be interesting to know once we do find it.

Also I'm a little confused. What is T2 and where is it located?
Secondly, does the red power line from fuse 11 go directly to the CDI unit, or is there a connector of some sort somewhere?
Thx

T2 is a 2 pole terminal connector near the CDI that has 2 reds and a brown/red (or brown/black)
The CDI harness from the engine plugs into it. It is the only connection from fuse 11 to the CDI.

Based on your last post, maybe it is in the ignition switch itself. This one is a puzzler....

Just trying to eliminate the easier stuff.
All fuses clean and tight? Intermittent in the fuse panel jumpers themselves? (Back of panel, the rivets are known to come loose over time.)

Loose plug at the firewall from ignition switch?

Battery positive terminal clamp clean and all wires from it tight?
Ground strap to battery clean and tight on both ends?

That is about all crossing my mind for now....

All right then Denis, I'll continue checking the various points that you brought up.
I must mention that I removed all fuses and cleaned the ends and the corresponding holders. I think those possibilities can be put behind me.
Today I'll remove the blower fan and check the multi pin connector at the firewall.
Can you tell me where in the Bentley manual is the T2 connection that you are talking about.
I want to locate it in the engine bay but would also like to see it on the schematics.
I'm still not sure how the ignition switch could have any bearing as the FP continues to run after the engine has died and I dont fully understand what effect there is in just turning the key to Acc and back to "run" that allows the engine to immediately start and keep running.
You're right, it is a mystery.
I'll keep you informed as to anything I might discover.
Thx

Don’t pull the blower fan. The male ignition switch plug is accessed from under the dash in the cockpit.
If fuses are confirmed good, then they are good.
If fuel pump still runs, then ignore switch failure. Problem is somewhere else.
To see T2 better, Download and print the factory color diagram for the ‘78, it is the same until ‘83 except for Lambda system.
https://www.dropbox.com/s/yjfoxfvwlci6lys/911_electrical_78SC_USA.pdf?dl=0

I will look at my unopened Bentley to see where it is.

Just looked in my never used for wiring Bentley, and confirmed almost none of the actual terminal connectors are shown in Bentley. Only the factory drawings show them.
Factory Legend describes approximate location of connector.
Screenshot of T2a. Definitely not drawn like that in Bentley...

http://forums.pelicanparts.com/uploa...1561912857.jpg

Thank you for the above info Denis. I did manage to find the T2 connection, right where you said I would. I pulled it apart and cleaned it as best I could. Apparently I had coated that connector with dielectric grease a couple of years ago and had forgotten about it. I keep thinking that an organised person should have a log of everything that he does to the vehicle, particularly in the engine compartment so that he can refer back should a problem arise.
So I cleaned the T2 connector and reassembled without dielectric grease. I also unplugged the connector at the fire wall to clean it. I double checked the connections to the battery and all was good.
Since we determined the FP was not causing the quitting problem, I removed the jumper and replaced the relay.
And went for a drive with my Lab.
The car ran well for the 30 min drive and then we stopped for 30 min to allow Hunter out for a walk. Of course that in itself doesn't prove anything as I've driven for longer periods before it would quit.
When I returned to the vehicle after our walk the car would not start. It turned over great but wouldn't catch.
Fortunately I was parked on a slope and was able to bump start the car in 2nd gear.

So I'll try to get more miles on it this week to see how it behaves.
Not very encouraging.

See my latest post under the thread "81 sc dying at speed"
Thx