CDI Box Troubleshooting Help

cgrossl · 08-27-2007, 05:54 PM

I've searched the forums here and learned alot, but I still have some questions. To make a long story short, I removed the blue cased, Perma-Tune CDI box because I was going to install an MSD 6AL box in my 77' 911, but then changed my mind. Now after reinstalling the Perma-Tune box, there is no spark. Before I reinstalled the CDI box, I installed a Pertronix ignitor, but I have since reinstalled the original points. They did look good when I put them back in the distributor.

The CDI box makes no whistling noise when the key is turned on. There is 12volts present on the middle wire going to the box. I checked the box using the bench test procedure and it shows to be good. Does the Perma-Tune whistle when it gets power?

All connections appear to be good. The coil only has about 1 volt on it when you turn the key on, not 12. Should the coil have 12volts across it. Or should it be more like 400v?

I've checked all the grounds and they all appear to be good.

Also, there are two wires that are under the CDI box that are unhooked. One is a red wire that has 12volts on it when the key is on. It has a male spade connector with a protective rubber insulator around it. I don't think that anything was ever plugged into it. There is also a brown wire that has a female spade connector on the end of it. It has no protective insulator on it. I don't think that I inadvertantly unplugged these two wires, but I could have I guess. I don't recall ever seeing a brown wire plug directly into a red "hot" wire. Brown wires are typically grounds.

Anyway, what other things should I check?

Cameron

HarryD · 08-27-2007, 06:55 PM

Hi Cameron,

Welcome to the forum. Try your search again using the terms bosch CDI and look for posts by early_s_man. There are several threads where he explains how to troublesoot CDI's.

The answer is already here.

2.7RACER · 03:10 PM

Cameron,
At pin C is the wire from the distributor. With points it's the only wire from the distributor. This wire will read ground when the points are closed. open when the points are open.
At pin A of the permatune is a wire that goes to pin A of the coil. Pin B of the coil goes to ground.
Some coils are numbered 1 and 15. 1 is ground and 15 goes to pin A of the permatune.
The wire from the distributor is shielded. The center portion goes to pin C of the permatune, the outside shielded part goes to ground. Make sure it is grounded.
Once power is applied to the permatune, the wire from the distributor to pin C of the permatune breaks ground and the permatune sends a high voltage from pin A to pin A of the coil.
Check each wire end to end for continuity. Check grounds for ground.
Make sure the distributor wire reads ground when the points are closed.

Edit: removed reference to high pitch sound from Permatune, thanks to HarryD. Bosch boxes make noise, Permatunes don't.

HarryD · 08-27-2007, 08:07 PM

Doug,

You better check your wiring diagram. Per Permatune (http://www.perma-tune.com/T-ignition-Porsche-911.html):
A = + or 15, coil hot primary terminal ( - or 1, coil ground primary terminal is connected to the engine ground).
B = Power from ignition switch.
C = Distributor breaker points.
D = Ground

BENCH CHECK OF THE IGNITION BOX (Perma-Tune only)

PIN A TO D = 3,300 Ohms +/- 100 is normal . Zero Ohm or lower than normal resistance indicates defective ignition coil damage to the box.

PIN B TO C = 100 Ohms, +/- 1 is normal. Open circuit or higher than normal resistance indicates ground loop or over voltage damage to the box.

PIN D TO MOUNTING FLANGE = Zero Ohms is normal. More than 0.2 Ohms indicates ground loop or battery terminal reversal damage to the box.

But, I hate to burst your bubble but AFAIK, Permatune boxes make no sounds, ever. You are thinking of the Bosch CDI.

If Cameron looks for Warren's posts, he will find a weath of trouble shooting advice that will help him track down his problem.

And, yes, I can easily post the thread I am thinking of, but it is better to teach a person to fish then to give him the fish. Since Cameron has indicated he had difficulty finding theappropriate post, I offered some hints where to look.

2.7RACER · 03:12 PM

Hi Harry,
Checked my permatune box for sound. It is quiet and it works fine. Thanks for the info. I've heard the pitchy sound from Bosch boxes.
I don't see any conflict with my description of wiring from distribuor to permatune or permatune to the coil. I use the Porsche factory manual for reference.
Actually quite simple wiring. I left out the tach wire. I wanted to keep the description simple.
I'll edit my post to reflect no sound from permatunes.
Oh, I don't mind passing out fish to hungry people.
Maybe we'll hear from Cameron.

HarryD · 08-28-2007, 04:14 PM

Doug,

I really do not mind handing out fish either but I thought Cameron needed to "discover" our guru.

Hopefully, he has found and corrected his problem by now.

cgrossl · 08-28-2007, 06:18 PM

I had already discovered your guru, I actually found a couple of them. I was just unclear about whether or not the Perma-tune was supposed to make noise or not, and I was unsure what those unhooked wires that are in the vicinity of the CDI box are for.

Anyway, the good news is, the car runs now. But, I'm not really for sure why. I reinstalled the coil and the CDI box after I did bench tests on both of them, then I did the test where you manually simulate the function of the points by unhooking them and then grounding the connector. I got spark right off the bat. I hooked everything back up, then, the car started right up. All that I did was clean the ground terminal on the CDI box, and clean the ground contacts that were under the coil mounting stud. I'm guessing that the cleaned grounds did the trick, but who knows?

My tach isn't working though. I'm guessing that I unhooked it during everything that has went on in the last few weeks. I'm also guessing that those unhooked wires might have something to do with it.

HarryD · 08-28-2007, 07:48 PM

Cameron,

Good to hear you got the car working. If you are using your points, the tach wire should be connected to a double spade lug on your distributor. One lug gets the black wire going to the Perma-tune and one gets the purple/black wire to the tach.

The wiring at the Distributor looks something like this (thanks dweymer):

cgrossl · 08-29-2007, 04:47 PM

Harry,
Thanks for the pic. My car doesn't have a two spaded connector coming out of the distributor like the pic shows. It only has one connector that the white wire that goes back to the CDI box. Is there somewhere else that the tach signal wire could be? I know it gets its signal from the points, but where else could it tie in to that wire?

I did check, and the tach is getting power. How easy is it to fry a tach?

HarryD · 08-29-2007, 06:29 PM

Look for a purple/black wire in your engine room. It should be near the dizzy or the CDI Box.