Makes no sense..


Your CDI was definitely providing spark, apparently timed, triggered, by the dizzy pickup.

What would be different with a different CDI..?

And now the alternator bearing(s) seemed to have failed...

Round Robin, traveling in circles?

I would suggest putting your CDI back to be sure something else didn't change.

Bearing failure in the alternator sounds likely. Maybe a spike in voltage affected your CDI?
With the belt off, spin the alternator and use a mechanics stethescope to listen for bearing noise. May only be apparent when loaded by the belt though.
The disclration on the fan is from heat. Front bearing is my initial guess.

Hey, you made progress!

In addition to what timmy2 said I would spin the fan and have a good look at the housing to see if there is any rubbing. Maybe not but worth inspecting.

"..Black circle...

Alternator bearing so loose you have in-and-out movement, play, in the position of the fan pulley vs the engine pulley. V-belt rubs on fan hub when shaft is most outward.

Just a guess.

I'll hook the old CDI back in tonight and see what she does. I spun the fan and it seemed to spin smoothly, with just a very quiet tick noise. It didn't shift on it's bearing noticeably.

I don't have the mechanic's stethoscope. I'll see if I can find one at my FLAPS. Looks like alternator work is in the offing!

I hooked up the old CDI and just got a little backfire and some exhaust out the popoff valve (air filter is off right now). I got a mechanic stethoscope and only hear the gentle ticking, just amplified.

There is definitely no rubbing of the fan and housing.

Time to take apart the fan/alternator assembly?

How many miles on that alternator?
If original have it rebuilt.

I don't think I saw this as a possible thing to check or that you had checked it (if I missed it, apoligies).... but did you check the multi prong plug that is by the reare "fuse" cover in the engine...? there is a multi prong plug that can get loose and stop the car, or make it run rough.... as well as one on the left side by the firewall that plugs in the wire harness... I'd go so far as to suggest separating, and pushing them both firmly togeather.

good Luck!

While you are at it, may as well send the CDI out too seeing as putting original back in didn't work well compared to borrowed unit.

I was thinking about this, but seeing how it immediately ran after switching the CDI makes me think it is something else. I checked all the plugs and wires I could find, and didn't see anything loose. We disconnected plugs and sprayed them with contact cleaner and re-plugged.

I know it is not the original, because '79 had an external VR and now it has one internal to the fan. But I don't know exactly how old it is. I could possibly find out by reading through my Big Binder of stuff.

I will dig into it Wednesday (busy tomorrow) and take apart the fan and alternator. Probably also the CDI later this week. The fact that it is firing regularly but not at the right time gives me hope it is something I can replace, like a capacitor or resistor. If not, I am priced into a CDI rebuild (about $350).

CDI "donor" car owner brave enough to let you try your CDI in his 911?

CDI rebuild or MSD Streetfire for $150 plus a resistor less rotor and some wire and connectors...

I'll have to look into what all one needs to do an MSD setup. If I get the CDI done professionally, it will cost about $350 by my reckoning (PartsKlassic). I did just get new stock wires/rotor/cap.
I am hoping that, seeing as it is working but the timing is off, it may be a resistor or capacitor which I could replace myself.

Of course, this is for after I get the alternator working. I could probably do a CDI swap with my friend when he's available again. Less risk seeing as CDI's only output is the coil trigger, and that is a pretty safe thing.

I checked some old pictures. The black line on the fan has been there for over 2 years (10K+ miles).

Contact Ingo (Ischmitz) and see what he is charging to repair the CDI these days.

I pulled the fan/alternator out and will open it up to check the bearings. That thing is a pain to remove!

I'll also open up the CDI and see if I can determine the point of failure. It doesn't look like that complicated of a device, electrically. No surface mount parts and I don't recall seeing even an IC. Maybe a diode, resistor, or some such is fried, resulting in the incorrect timing.

Look carefully, closely, at the stator winding support/insulation.

At ~90k miles mine were burned so badly that the stator windings were intermittently shorting to ground via the metal supports.

Thanks timmy2, there is a wealth of info there. RIP Warren.

Another good thread on ours in particular: http://forums.pelicanparts.com/porsche-911-technical-forum/226517-history-bosch-cdi-toubleshooting-info-parts-list-changes-schematics.html

Ok, I'll take a close look there. I suppose that doesn't result in the awful noise, but if I'm in there I should make sure everything is in top shape.

No experience, NONE, repairing Bosch specifically but years of experience with other CDIs and in electronics otherwise.

As battery voltage rises ZD1, 10 watts, must consume more and more power, so I would nominate it for being the most likely failure point arising from battery overcharging.

I don't understand the recommendation for substituting a lower voltage zener diode for ZD1. ZD1 protects the 2N3055 from collector breakdown by limiting the collector voltage rise but the secondary effect is to limit the transformer's secondary voltage.