Working 3-pin CDI in SoCal?

[Bulldozer27]

I have a bone stock '71 911E engine that has no spark. I have swapped out the coil, distributor rotor and cap, spark plug wires, ignition points (and also swapped points with Pertronix). Yet I still have no spark. My last two tests are the CDI and the CDI wiring harness.

I should point out that the CDI harness gets about 11.5v at the Red wire with the ignition in the on position as opposed to positive an negative battery terminal being 12.5v.

Does anyone here in SoCal have a known working CDI that they can loan me for testing purposes? I don't want to invest in a CDI Rebuild at Pelican just yet given all of the money I have spent already just getting to this point.

I'm in the San Diego area and wouldn't mind driving up to LA to borrow one if any of you here were willing and could be so generous.

[Trackrash]

I'm guessing that you are not hearing the whine from the CDI unit? Heck, I had to replace, actually get rebuilt, my CDI back in the '80s.

I would recommend taking your car to Black Forest and have them test it.

[nathanbs]

I have one that you can borrow or maybe buy and if you don’t need it I can refund you. Whatever makes sense. Either way I have a working spare

[ischmitz]

you can test the 3-in CDI yourself.

- turn ignition on (must hear whine)
- Connect spare spark plug to output of coil and ground
- close points and there needs to be a spark

Also, ohm out the points and make sure when they close there is GND on the trigger (Pin C of the 3-pin harness connector)

Else you can ship it up here (Santa Barbara) for test and possible fix

Ingo

[Bulldozer27]

Originally Posted by ischmitz

you can test the 3-in CDI yourself.

- turn ignition on (must hear whine)
- Connect spare spark plug to output of coil and ground
- close points and there needs to be a spark

Also, ohm out the points and make sure when they close there is GND on the trigger (Pin C of the 3-pin harness connector)

Else you can ship it up here (Santa Barbara) for test and possible fix

Ingo

I have Pertronix instead of points. Can I still do this test, and if so, what do I do different?

[Trackrash]

How I tested my 6 pin CDI.

[ischmitz]

The Pwrtonix unit acts as a switch. I would create 4 extension wires (male spade to female spade with 10 inch of 12 gauge insulated wire) and put them between the CDI and the car harness connector.

That will allow you to selectively disconnect the trigger wire (pin C) and touch it to the housing. This should release a spark.

For a little more sophisticated test rig I built a little trigger circuit and a bench setup:

[Jonny H]

Originally Posted by Bulldozer27

I have Pertronix instead of points. Can I still do this test, and if so, what do I do different?

What ischmitz said about spare spark plug, then:

Just disconnect the black wire from the Pertronix.

Ignition on. Then ‘drag’/touch spade (on original wire) on engine case. Spark generated when released from case (ground).

[Bulldozer27]

Originally Posted by Jonny H

What ischmitz said about spare spark plug, then:

Just disconnect the black wire from the Pertronix.

Ignition on. Then ‘drag’/touch spade (on original wire) on engine case. Spark generated when released from case (ground).

OK, I did all of this and got no spark when the black wire was released from the ground. Is it reasonable to say that the discharge capacitor has gone bad inside the CDI, hence the need for a rebuild?

[ischmitz]

that sounds like one possible conclusion even though this failure mode is more consistent with 6-pin boxes.

[Bulldozer27]

Just want to update this thread by thanking ischmitz for his recommended diagnostic test for my CDI. I did exactly as he said, got no spark, sent it to our hosts for rebuild, and now my no-spark problem is solved. Engine starts up like new.

As per the service report that accompanied my rebuilt CDI, there was a faulty solder joint as well as a failed ZD1 zener diode. Hopefully this info will be useful data for someone else here in the future.

[mysocal911]

Originally Posted by Bulldozer27

Just want to update this thread by thanking ischmitz for his recommended diagnostic test for my CDI. I did exactly as he said, got no spark, sent it to our hosts for rebuild, and now my no-spark problem is solved. Engine starts up like new.

As per the service report that accompanied my rebuilt CDI, there was a faulty solder joint as well as a failed ZD1 zener diode. Hopefully this info will be useful data for someone else here in the future.

So you didn't consider the one you thanked as a source for CDI rebuilding?