CD ignition problems

corysurf · 02-01-2002, 02:46 PM

I have a '71 911T and it will not start. The engine turns over when started, but there is no spark. I made sure that there was 12v and ground to the CD unit, but there is no power coming out of it going to the coil. I assume that I need to replace the CD unit, but I wanted to make sure before I spent the money on a new unit. Thanks.

Early_S_Man · 02-01-2002, 03:52 PM

First thing to check is the points! If they look OK, take the trigger lead off the distributor, and touch it to ground a few times after rigging up a test spark plug to the coil center terminal.

Does the CDI-unit whine when the ignition switch is on?

Does the coil have any oil leakage or signs of overheating?

304065 · 02-01-2002, 04:18 PM

Can you hear it whine? The unit contains an inverter and transformer to generate the high voltage to charge the capacitor, and just like a flash unit in a camera, you should be able to hear it whine.

By good ground, I assume you cleaned the brass terminal on the brown wire that bolts to the body sheetmetal behind the "console." The ground that comes off the metal tab on the CD box at the bottom goes to a braided wire that connects to the engine at two points- but the trans ground is pretty lousy, so if you don't have continuity between the brown wire, the console and the CD box, that could inhibit good operation.

Do you have continuity between the red terminal in the three-way plug that goes into the bottom of the CD box and the bottom fuse (#1). Also, I would check for contiunity between the black with purple lead to the the side of the distributor, and between the blue with yellow lead to terminal 15 at the coil (the coil positive).

I don't know how to measure the CD box output but my guess is that when the capacitor discharges, it's VERY high voltage and could result in a really bad hair day for both the multimeter and it's owner . . .

I would guess that it's more likely that a connection somewhere would have failed than for the CD box to go bad, but it certainly could happen.

Good luck! Wish I could help more but I have converted to MSD 6AL (with rev-limiter!)

corysurf · 02-01-2002, 05:23 PM

Thanks for all the input, I think it will help. Hopefully it will be running again soon.

Zendalar · 02-02-2002, 03:13 AM

If the CD box does not whine, you could try hitting it. Yes, with your fist to the side of CD box.

My CD box had solid copper wires inside that in time caused the solder joint to go bad (wire comes loose). Sometimes it worked like a charm but then I had to hit so that it came back alive. The problem was one solid core wire that was connected to the electrolytic condensator inside the CD box had poor soldering.

If you are getting rid of the broken CD box

I will gladly take it.