No Spark

[chris belyea]

Hi,

A few months ago, I started to have problems with my 71 911. I was driving and the car just cut off. After about sitting on the road for about 5 minutes, the car started and I was able to get back home. The following weekend I wanted to go on a test drive to see if I could replicate the problem and the car shut off in my driveway after running for about 15 minutes. Again, I couldn't restart the car but after sitting for a few minutes, it would restart. So I pulled out the 3-pin CDI box and sent it off to have it checked out. The CDI box tested fine. When I reinstalled it, I cannot get it to start at all now.

I purchased a new coil and still no spark. I confirmed that I had power to the CDI box when the ignition was switched on and when in the starting position. I did notice that the voltage did drop at the CDI box to about 10.7v during the test. I have checked the wiring and grounds in the engine compartment and still can't obtain a spark. I have a dual battery setup and the batteries are about 3 to 4 years old. Are the CDI boxes susceptible to a voltage drop? I've had a modern turn over all day long and not start and was told it was the battery. Wasn't sure if this would happen with these older cars.

Any suggestions? I'm sort of at a loss.

Thanks

Chris

[rowingone]

Check distributor, points . . .wire attachment to coil.

[mysocal911]

Originally Posted by chris belyea

Hi,

A few months ago, I started to have problems with my 71 911. I was driving and the car just cut off. After about sitting on the road for about 5 minutes, the car started and I was able to get back home. The following weekend I wanted to go on a test drive to see if I could replicate the problem and the car shut off in my driveway after running for about 15 minutes. Again, I couldn't restart the car but after sitting for a few minutes, it would restart. So I pulled out the 3-pin CDI box and sent it off to have it checked out. The CDI box tested fine. When I reinstalled it, I cannot get it to start at all now.

I purchased a new coil and still no spark. I confirmed that I had power to the CDI box when the ignition was switched on and when in the starting position. I did notice that the voltage did drop at the CDI box to about 10.7v during the test. I have checked the wiring and grounds in the engine compartment and still can't obtain a spark. I have a dual battery setup and the batteries are about 3 to 4 years old. Are the CDI boxes susceptible to a voltage drop? I've had a modern turn over all day long and not start and was told it was the battery. Wasn't sure if this would happen with these older cars.

Any suggestions? I'm sort of at a loss.

Thanks

Chris

Who did you send it to? Call them and indicate your problem. Maybe even suggest that they may have damaged it, and need it repaired!
On second thought, find another source for repair.

[chris belyea]

I sent it to Bob Ashlock. He had rebuilt it about 4 years ago and ran several test. I have been communicating with him and he's been very helpful. I've been running all the trouble shooting he has recommended. I just hate to keep bothering him so I thought I would reach to the folks here. It is possible that since the problem was intermittent, that it worked at his shop. Although he did run the test over night and put it in his own car and found no issues. It could have gotten damaged in post. So it's possible it's the CDI. Just trying to rule out what ever I can.

BTW, I have checked the points, cleaned them and reinstalled them. I checked that I had continuity from the distributor to CDI.

[mysocal911]

Originally Posted by chris belyea

I sent it to Bob Ashlock. He had rebuilt it about 4 years ago and ran several test. I have been communicating with him and he's been very helpful. I've been running all the trouble shooting he has recommended. I just hate to keep bothering him so I thought I would reach to the folks here.

It should be the responsibility of those doing rebuilding to help customers solve ignition problems.
Hopefully your rebuilder provides at least 5+ years like some with over 35+ years rebuilding CDIs, e.g. www.systemsc.com

It is possible that since the problem was intermittent, that it worked at his shop. Although he did run the test over night and put it in his own car and found no issues. It could have gotten damaged in post. So it's possible it's the CDI. Just trying to rule out what ever I can.

Yes.

BTW, I have checked the points, cleaned them and reinstalled them. I checked that I had continuity from the distributor to CDI.

1. Use a testlight to check the points - alligator clip on +12V & pointed end on the CDI points input
Flashings should occur while cranking or just manually opening the points.
2. Since you replaced the coil, that eliminates the coil.
3. The CDI should provide a spark when the battery voltage as low as 9-10 volts.
4. Typically, you should hear a buzzing sound while powered on.
5. A spark usually occurs when the CDI is powered off too.

It doesn't get any more comprehensive than that! It's less than a 5 minute effort.