Behind the green wire

[spoke]

Originally Posted by Aurel

Now is time for an update. I finally figured out what was preventing sparks, and now have ignition again.

I checked again the voltage at the CDI box, and even without cranking, it was only 6.5-7V.
The voltage at the front fuses was a solid 13V, and the voltage at the engine fuses was only 6.5-7V.
I checked my ground connection but that was fine.
I opened the 14 pin connector, and sure enough there was a connection holding by a thread that broke immediately. I resoldered it and voila, my ignition is back.

Fantastic that you got your 911 running again. Good detective work. Connections can cause all kinds of strange issues and lead to dead ends when testing components.

I'm puzzled by one thing though. You say you measured voltage at the CDI box was 6.5-7V. But previously you mentioned the voltage at the CDI to be 13.1V. Were these the same measurements at the same place on the CDI?

[Aurel]

Originally Posted by spoke

Fantastic that you got your 911 running again. Good detective work. Connections can cause all kinds of strange issues and lead to dead ends when testing components.

I'm puzzled by one thing though. You say you measured voltage at the CDI box was 6.5-7V. But previously you mentioned the voltage at the CDI to be 13.1V. Were these the same measurements at the same place on the CDI?

Yes, that is what misled me too. I did see the correct voltage at the fuse that feeds the CDI box, then two weeks later it was half that. I think a very lose contact inside the 14 pin connector may have caused this.

[PeteKz]

I've seen frayed wires at the 14 pin connector too. There must be enough vibration and movement of the engine harness to cause those connections to fatigue and break. I will guess that several other of your connectors are hanging by a few strands too.

[Aurel]

Here is another update: the car starts right away and I got the idle set and stable at 950 rpm, all good…but the advance I am reading with my strobe light is the maximum mark I have on the pulley, which was 35 degrees BTDC. Also, if I give it a little gas, it backfires in the exhaust and cannot pick up much rpms.

Is it possible that my distributor is one gear tooth off? Would one tooth cause the advance to shift by 35 degrees? If that is the case, it will be an easy fix.

[mysocal911]

Originally Posted by Aurel

Here is another update: the car starts right away and I got the idle set and stable at 950 rpm, all good…but the advance I am reading with my strobe light is the maximum mark I have on the pulley, which was 35 degrees BTDC. Also, if I give it a little gas, it backfires in the exhaust and cannot pick up much rpms.

Is it possible that my distributor is one gear tooth off? Would one tooth cause the advance to shift by 35 degrees? If that is the case, it will be an easy fix.

Typically occurs when the green wire connection is reversed.

[Aurel]

Originally Posted by mysocal911

Typically occurs when the green wire connection is reversed.

Ok, if that is the case it will be an easy fix too, since I made connector spade quick connects to change those polarities. I will try it!

[Aurel]

Originally Posted by mysocal911

Typically occurs when the green wire connection is reversed.

YESS! I just switched the wires, and she is now screaming like never before!
Thank you so much, Dave. You saved me from pulling the distributor one more time and get nowhere…

[LJ851]

Originally Posted by Aurel

YESS! I just switched the wires, and she is now screaming like never before!
Thank you so much mysocal911, you saved me from pulling the distributor one more time and get nowhere…

Switching the wires does more than change the timing, it throws off the rotor phasing to the cap which is why it runs so poorly in addition to the timing change.

[Aurel]

Originally Posted by LJ851

Switching the wires does more than change the timing, it throws off the rotor phasing to the cap which is why it runs so poorly in addition to the timing change.

The part that threw me off is that I checked the signal from the green wire going to the cdi box with the oscilloscope and it looked correct. But obviously, I can tell now that the wires are switched, I was wrong.