Bouncing Tach when Cold, and Zap Noises

[timmy2]

Waiting for parts to arrive to replace green wire.

[OsoMoore]

I hooked up the oscilloscope and when I try to measure the green wire CDI input, the scope's presence causes the CDI to behave differently.

Engine definitely behaves better when at operating temperature - almost no misfires at all. The main time of the phenomena is before operating temp is reached.

The CDI box doesn't get particularly hot, and I tried the water spraying idea. It had no effect.

Current plan is to replace the coil and the green wire, and open up the distributor to clean/rebuild it. Any ideas on what parts I should order to aid in that step? I'm about to order the green wire and coil and don't want to re-order when I discover I need a washer or some such.

I'd like to thank everyone who is following along and helping with this endeavor - this community is amazing!

[wwest]

The best way to use an O'scope with a coax connection is to have dual channel O'scope in differential mode. Otherwise you must be certain the scope ground connection is grounded/connected ONLY to the ground return connection right at the CDI.

Just as a lark connect the O'scope to the 12 volts at the CDI connector and see if the 12 volts is intermittent, maybe the same with the CDI connector ground return.

But would you remind first removing the v-belt before I abandon my theory completely?

[OsoMoore]

Originally Posted by wwest

The best way to use an O'scope with a coax connection is to have dual channel O'scope in differential mode. Otherwise you must be certain the scope ground connection is grounded/connected ONLY to the ground return connection right at the CDI.

Just as a lark connect the O'scope to the 12 volts at the CDI connector and see if the 12 volts is intermittent, maybe the same with the CDI connector ground return.

But would you remind first removing the v-belt before I abandon my theory completely?

Sure, I'll try removing the belt. We tried pulling the alternator light in the dash last week, and it still did it's sparky thing.

The scope I have is an old Heathkit without a lot of features, but I'll see what I can find on the other connections.

[OsoMoore]

Originally Posted by hsftyh

How do your points look? I had a similar situation but mine would drop off all together. I found the points were shot.

It has a magnetic pickup - no points.

[timmy2]

PartsKlassic has a rebuild kit for your distributor. Bushings, shims etc.
Call them if you can't find it in their site.

[OsoMoore]

I'm seeing some people comment on running an MSD coil on their normal stock CDI boxes. Is that generally considered OK? They are a lot cheaper...

[OsoMoore]

Originally Posted by OsoMoore

I'm seeing some people comment on running an MSD coil on their normal stock CDI boxes. Is that generally considered OK? They are a lot cheaper...

UncleEnzo confirms he is running the MSD coil and stock rotor on his SC, without any issues. Assuming some other tests don't eliminate the coil as a possible culprit, I'm planning to get this one 1979 Porsche 911 SC Targa - Ignition - Page 3

[timmy2]

I have been running the MSD Blaster 2 high vibration coil on my stock CDI system for 3.5 years no problem.

[wwest]

Originally Posted by OsoMoore

UncleEnzo confirms he is running the MSD coil and stock rotor on his SC, without any issues. Assuming some other tests don't eliminate the coil as a possible culprit, I'm planning to get this one 1979 Porsche 911 SC Targa - Ignition - Page 3

Inductive power storage type coils like the one linked should only be used with a Kettering type ignition system, mechanical point or solid state substitute.

Transformer type coils, E & L core laminations, would provide the best use of the capacitor charge of a CDI systems.

http://www.streetsideauto.com/p/accel-remote-mount-super-140011/?utm_source=googlepepla&utm_medium=adword&gclid=CJKHjpKB9MQCFY-TfgodlKoAMA

[OsoMoore]

I've now got new Beru factory spec wires (with shields) on the way and a new green wire as well. Unfortunately, PP reports that the spark plug wires are a specialty item and don't ship until Monday. So this weekend will be a time of pining away for the open road.

The wealth of advice is a little overwhelming, so I am going to try to slow down and work through the maintenance items first before I do something crazy like take the alternator apart.

[OsoMoore]

New Beru wires did not address the issue.

I just finished getting the new green wire rigged. I hate crimping!!!

Before I put the distributor back in and try it (always seems I have to rotate 710 degrees to get back to TDC) I thought I'd remove the vacuum part of the distributor via those 2 little screws.

It seems connected somehow internally, and while it can swing away, it can't come away as one piece and I can't really see in inside. I think I saw a little bit of wire, but can't see it now. I do see lots of what looks like magnetized metal dust, arranged in the little magnetized patterns you see in such circumstances. Is this OK?

Should I be able to remove the vacuum unit on a stock SC distributor? Or should I just put it all back together and see how it goes?

[tirwin]

You shouldn't have to remove the vacuum part of the dizzy. Maybe I'm confused. Pics might help us see what you're saying better.

[wwest]

Originally Posted by OsoMoore

New Beru wires did not address the issue.

I just finished getting the new green wire rigged. I hate crimping!!!

Before I put the distributor back in and try it (always seems I have to rotate 710 degrees to get back to TDC) I thought I'd remove the vacuum part of the distributor via those 2 little screws.

It seems connected somehow internally, and while it can swing away, it can't come away as one piece and I can't really see in inside. I think I saw a little bit of wire, but can't see it now. I do see lots of what looks like magnetized metal dust, arranged in the little magnetized patterns you see in such circumstances. Is this OK?

Should I be able to remove the vacuum unit on a stock SC distributor? Or should I just put it all back together and see how it goes?

The vacuum motor bellows is attached to the timing "swing plate".

" metal dust..." " is this okay.?"

No, most definitely NOT.

Metal particles in the magnetic field of the pickup can cause all kinds of random signals.

Have a professional have look.

[OsoMoore]

Originally Posted by wwest

The vacuum motor bellows is attached to the timing "swing plate".

" metal dust..." " is this okay.?"

No, most definitely NOT.

Metal particles in the magnetic field of the pickup can cause all kinds of random signals.

Have a professional have look.

Yikes! I'll post some pictures and ask around for a local expert.

[OsoMoore]

Here are some shots from the side. You can see the little metal bits that are aligned with the magnetic field inside. At least, that is what I suppose.

[timmy2]

Originally Posted by timmy2

PartsKlassic has a rebuild kit for your distributor. Bushings, shims etc.
Call them if you can't find it in their site.

As I posted earlier..
And:
83 SC Ignition Distributor Bushing Replacement

Distributor service (Clean and lube) real easy without removing the pinion gear!

[Turpin]

Subscribed...
Having the same issue with the bouncing tach...

Russ

[OsoMoore]

Originally Posted by timmy2

As I posted earlier..
And:
83 SC Ignition Distributor Bushing Replacement

Distributor service (Clean and lube) real easy without removing the pinion gear!

I called them last week and they can build me a rebuild kit. Their guy suggested I replace my spark wires and green wire first (which I have now done, with parts from Pelican).

Looks like I'll be calling him back!

[wwest]

Originally Posted by OsoMoore

I called them last week and they can build me a rebuild kit. Their guy suggested I replace my spark wires and green wire first (which I have now done, with parts from Pelican).

Looks like I'll be calling him back!

I would suggest disassembling yours first just to be sure it's rebuildable.