ignition system help

I have just installed a 77 2.7 CSI in my l974 911S. Everything went as it should, engine ran great for about 30 minutes.
After setting for about an hour I tried to restart the engine. It fired, died, then would not restart. I have a Haynes manual but it is not very good with information on troubleshooting the ignition system. The CDS is still whistling, but the coil is not firing. The points are set correctly.
Does anyone have any ideas or information where I can get help troubleshooting this systm?

Do you have an electrical multimeter? Either analog or digital will be fine. All that will be needed is a low resistance range (Ohms) and a high voltage DC range (600-1000 Volts) for testing your ignition. Alligator clip leads will be needed, not pointed probes! If you have an assistant, that is fine. If not, you will need a remote starter switch. You will need a 22 mm socket and ratchet, or box-end wrench to turn over the engine. All tests will be made with the hot center lead taken out of the distributor and laying near sheet metal or engine block!

There are static and dynamic tests that you can make on all of the ignition system components. Besides the wiring interconnecting them, there are only three major components in your ignition system, the distributor, CDI-unit, and ignition transformer (coil). All can be tested by the owner/mechanic! You say the CDI-unit still whistles, that indicates that the high-voltage inverter is working, but doessn't say whether it is getting a trigger pulse, or whether the trigger circuit is working. To test the CDI-unit and coil together, with the ignition switch turned on, remove the center lead from the distributor cap, and the Black wire with Purple stripe from the spade connector on the side of the distributor. Place the high-tension lead removed from the distributor cap near a good grounded surface (1/8" to 1/4" or so) and remove any part of your body from the vicinity! Take the Black/Purple trigger lead wire in hand and momentarily touch the connector to a grounded bare metal location, then remove and touch back to ground a few times (1-6 times) and see if a spark jumps from the high-tension lead to ground. It should pop rather loudly and be a strong, rather than a weak spark! If so, congradulations, your CDI-unit and coil are fine! Your coil has two bolt-on connections, one is a brown ground wire that you need to make sure is not loose or corroded at either end. The other wire, a Light-Blue with Yellow stripe is high voltage (350-600 Volt DC pulse signal to the igniton transformer. To test that pulse signal connect alligator leads from your multimeter, negative (back) to a secure ground connection, and red (positive) to the Blue/Yellow wire on the coil -- with the multimeter range set to 600-1000 Volts DC. Again, take the Black/Purple wire and touch to ground multiple times and look for the high voltage pulse to 'kick' the meter each time. If you see the voltage pulse but get no spark, and have verified the resistance at the gound connection at the brown lead of the coil to be less than 1 Ohm with the multimeter, then your coil is bad. If you do not see the pulse, turn off the ignition, and remove the large three-pole connector on the bottom of the CDI-unit and check the connector for corrosion or a loose connection! If the coil is indicated to be bad, after removal from the engine, test with the multimeter to see if the primary winding -- Brown lead to Blue/Yellow lead is good or open (less than 1000 Ohms) or if the secondary winding is good or bad -- usually 10,000 to 30,000 Ohms if good, open or 'infinite' if bad ... Brown lead to HI-V lead. If CDI-unit and coil are OK, the distributor will need to be removed from the engine for closer inspection and testing. With 22 mm wrench, turrn over the engine to firing position for cylinder #1, as marked on the distributor body with a stamped 'notch' ... then remove the 13 mm nut and washer holding the distributor clamp in place, and remove distributor and clamp as one unit. On the bench, remove the rotor and dust cap. Inspect the flexible ground strap from the body of the distibutor to the rotating point plate connected to the vacuum retard diaphram link. If that flexible ground wire has broken near the 'spot weld' ... that is the reason for NO SPARK -- NO START!!! That happened to me in 1982, and it will kill your engine -- DEAD, until the ground wire is repaired! If the ground wire is OK, look at the lead from the points to the connector for the trigger lead outside. If nothing is visibly loose or damaged, connect the multimeter leads to the external trigger connector and distributor body, with the range set to low Ohms (200 or less) and rotate the timing gear. When the points are closed, you should see a resistance of less than 1 Ohm, and open should read infinite! If there is any doubt, the points should be replaced, and Bosch is the preferred replacement! Point-triggered CDI ignition systems have very long point life, but replacment every five years or so is a good idea. While you have the distributor out, you should check for smooth operation of the rotating point plate in response to the vacuumm retard diaphram ... any sticking or resistance is indicative of a need for cleaning and lubricating with Bosch grease. The cenrifugal advance mechanism should be checked for smooth operation, too! It, too, needs cleaning and a fresh supply of Bosch grease, if it is sticky. Hope this helps! Good Luck!

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Warren Hall
1973 911S Targa

Sometimes a little grease on the points will keep it from firing.

Try squirting them with some carburator cleaner and drying it off with a paper towel.

Joe

I had problems about four months ago with my SC. It just up and died on me while I was cruising @ approx. 65 mph. I checked all the normal stuff. . .Fuel/batt. ignition ect. Still I could not get any spark out of my coil. Thinking that my coil was bad, I bought a new unit. Still no luck. . . I bet I ran a voltmeter across every wire possible. Finally I was at ends. . . I had the car towed up to Boisie to my mechanic. he looked at it for over a week testing everything he could think of, when his apprentice just happened to be going over my fuse panel and noticed a screw that holds the wire to the fuse block was loose, so he tightened it. Next thing you know it fired right up. The kicker is, the loose wire went to my left high beam headlight (i think)!!!
He said it had to do with the ground system these cars have. I dunno. . .Anyway hope this helps. ( that damn screw cost me $800.00 though...CDS/coil)

Lee Pate

_____79 SC targa

thanks for all the information.i have not had a chance to get the car back on the highway,but it seems to be running fine around the subdivison. i'm a little gun shy to take it back on the road when it can determine what caused the problem. thanks again.