Ignition Problem

Yeager · 09-12-2006, 08:42 PM

I have a 74 911 S with a Permatune CDI, Bosch coil, and Pertronix electronic ignition.

I am not getting a spark from the coil.

However, if car sits overnight it tends to fire right up but after a minute or two dies and will not crank again.

I have performed the coil ohm test and it is good. I have checked the supply voltage to the CDI and it is good. I have checked the resistance of all of my wires and they are good. I have checked and rechecked for ground loop problems and cannot find any. I have pulled on wires to try and find shorts and have found none. I have removed the CDI box and performed ohm tests and it is good - as far as I can tell. I have removed the relay panel and looked for bad connections and have found none. I have also disconnected the black/violet tach wire and nothing changed. All other electrical items work well. I have never had an issue with the starter not turning or any other electrical issue that would indicate a ignition switch problem.

Two things that I have not checked and would like to know how are:

How do I check the signal from the petronix ignition to the Permatune CDI (3 wire)?

How do I check the voltage to the coil when starting? I have checked with the ignition on and it has good voltage to the A terminal.

Also, I do not see any external ground wire on my distributor. Is this normal?

Thanks for any help. I have spent countless hours reading and testing without any progress.

Yeager · 09-13-2006, 05:27 AM

bump

Gunter · Gunter's Garage

Permatune is not regarded very highly.
If the module is suspect, try and find a used Bosch CDI 3-pin.
As for testing various values, hopefully some expert will chime in.

azasadny · azasadny's Garage

Do you have an old "derelict" car alarm installed? That was my main problem and the symptoms I had sounded like yours. Turns out there was a "Hoffco" alarm installed into the wiring harness in 1985 and it shut down the ignition/fuel pump circuit after a period of time and was intermittent. Drove me crazy, quite literally!!

Yeager · 09-13-2006, 07:19 AM

I have not found an alarm. Where would it be located if I had one. I have removed door panels and relay panel and looked under dash and have found nothing that looks like an alarm box. All of my fuel test show I do not lose pressure when the car shuts down. And when I go to recrank fuel pressure is available. But the spark is gone.

Thanks,
Mike

Yeager · 09-13-2006, 07:22 AM

I have ran across several people bashing the permatune box and I am more than willing to trash it but I want to make sure it is the culprit.

Thanks.

Yeager · 09-13-2006, 08:32 AM

bump

jstobo · 09-13-2006, 08:53 AM

To make sure it is not the pertronix, put some points back in. Gap them and try to start. If problem is still there, then I think it is probabally the Permatune. If problem goes away then you know it was the Pertronix. The Pertronix have a 30 month warranty so you may be able to get a new one for free. By the way, I replaced my points with the Pertronix and love it. But I also have a MSD which I think are better quality than the Permatune for aftermarket CDI systems. Hope this helps.

Jim

Early_S_Man · 09-13-2006, 11:52 AM

Mike,

Is your Permatune unit Blue or clear anodized? The Blue units are usually quite reliable ... the clear/silver ones not so!

You can test the CDI input signal from the Pertronix Ignitor with a 12 Volt test lamp connected to the triple fuse block. If you aren't getting an interrupted ground signal during cranking, then the problem is with the Pertronix Ignitor. Most people say you should carry a spare set of points with you at all times for when the Pertronix fails. That doesn't say too much for the expected reliability of the Pertronix to me!

History of Bosch CDI ... toubleshooting info, parts list changes, and schematics ...

At this point ... with the wiring and connectors 32+ years old, I suggest thorough cleaning of the Faston connectors with 91% isopropyl alcohol on Q-tips, rinsed with distilled water and dried, then cleaned with 9% pickling vinegar, then rinsed and air dried again as indicated in the following diagram:

Your Permatune can be tested with a remote starter switch wired to the #50 starter solenoid lead #1 Yellow wire at the forward 14-pin connector on the electrical panel on the left side of the engine compartment. A permanent remote starter switch on that panel can be helpful.

A test can also be done with the following circuit I call my junk-box calibrator -- it can also be built with parts from Radio Shack or any electronics supply store:

Good luck!