Help Request: '78SC Smoke out intake, Quit running. It's not the CDI!

[b. hilliard]

Thank you rwest, good intel on the alternator.
This begs the question; can starting/ running the car (even just to test the alternator and voltage regulator, etc) give the potential of spiking power and actually taking out my new CDI? The last thing I need is to ruin the new one which leaves me unable to diagnose! It seems to me it would be a poor design if a voltage spike from a failing regulator could take out the "brains" of the injection system too!!
I will be able to do some tests tomorrow, so I'm getting a pretty good list of potential issues.

[mysocal911]

Originally Posted by b. hilliard

Thanks rwest, I feel like I've heard that too regarding the bouncing tach but cannot figure out what the various symptoms/ solutions are. Even with the known good CDI that I bought and swapped in the tach bounced, although it produced a nice spark where the the original CDI did not. So the car ran, but not for long!!

What does this mean, e.g. you saw the CDI run perfectly on another car?

[b. hilliard]

Hi mysocal911, I bought a second CDI as a “known good CDI” brought it with me when troubleshooting the issue (the car is 200 miles away from me) The new CDI produced a nice spark. Knowing that that was good, I left it installed while trying to find the other issue that still plagues it, causing the car to die out.

[Demetri]

My bouncing tach issue was caused by my old battery.

[b. hilliard]

Hi all-
A partial update for those interested; I made a list of everything people have mentioned and dug into the car this weekend. It was slow going without many of my tools and no lift, but essentially was able to cross everything off the list except one, I ran out of time to try starting and driving it again!
Every relevant wire, coil/ pickup, ground and fuse block was tested for resistance/ continuity, cleaned and reassembled. The final thing that got my attention however, may prove to be the most crucial. The huge Interstate battery that's been in there for a while and always sounded healthy and performed as expected, was on my trickle charger all last week. I disconnected before doing the 2 days of work and the last thing I did was hook up my multi meter so I could watch it during load, idle and then test driving. Initial reading? 12.1V. Crap, this could be a smoking gun....
I'll buy a new battery this week and head back to VT in a few days to put all the pieces of the puzzle together. Hopefully it runs as it should with all this new work and a fresh battery, the Hilliard Vintage Grand Prix weekend at Watkins Glen is coming fast!

[Ian Comerford]

As above I would solve the bouncing tach first and look at either a failing voltage regulator or alternator as the most common causes

[Tom_in_NH]

Bouncing tach is often an indication of a bad voltage regualtor.

[zuch]

I'm in Williston Vermont. Yell if your car is close and you need a hand. I have a lift, oscilliscope, tools, etc.

[b. hilliard]

Hi Zuch, an amazing offer but I'm up in the Northeast corner so a good distance away. Thank you so much though!!

[b. hilliard]

Another update as I was able to spend some time with the car today. Installed a fresh battery and started the car. Once warm, I re-timed it at idle and kept hearing an odd noise that seemed to be coming from the distributor. Also odd to me was that the timing mark seemed to jump around a lot and occasionally the timing light failed to flash consistently. Was it misfiring, perhaps?
I installed a fresh Bosch cap and rotor (the old Beru one I removed has only 3-400 miles) and it sounded better but still made some low-volume metallic honking sound as the distributor spun around. Started the car again, warmed it a bit and tried some 1st gear driving.
Tachometer still bouncing. Engine seemed to run OK, not great. A bit rough still, especially at idle/ low RPMs.
Made it a 1/4 mile up the road, turned around and it promptly died coming back down the hill.
It seemed like it just lost all spark again, once it started warming up.
I pulled the distributor to check the resistance and continuity at all 6 points as we spun it around by hand. That's when I discovered the same metallic honking "noise" as I spun the distributor...it sounded like metal binding up, and could feel the vibration, like a dry bearing. My understanding is that there is only bushings inside (no bearings), so how are these lubricated? Do they run dry? Vertical and axial play seem very minimal, but the sound is horrible when I spin by hand and give it some vertical pressure. Please see attached video for the sound!

https://cdn.mileshilliard.com/porsche.mp4

[rwest]

There is a felt pad down the shaft under the rotor that gets a few drop of oil occasionally.

Have you checked voltage at battery when at rest and when charging yet? That should tell you if your alternator is acting up.

[b. hilliard]

Hi rwest, yes the alternator/ battery / system is spot on and looks to be cleared in all situations.

The felt has been oiled a few times over the years, particularly recently but maybe it’s not been enough? Is that the only way the brass bushings are lubricated?

[A930Rocket]

I’m not sure of the names, but is it possible one or more of the 6 point star is rubbing on the brown circle within somewhere?

Disassemble it, and spin as you take parts off to determine where the noise is.

[b. hilliard]

Yes, something seems amiss inside. Sadly I don't have all my tools with me so I'll have to bring it home and tear into it I think. Am hoping someone familiar with these distributors can tell me that either it sounds normal and just needs cleaning/ re-oiling, or I should get a whole rebuild kit and deal with it later. Getting it running in time for Watkins Glen Vintage races is fading fast!