Electronic ignition - Revisited after I gave up!

[Arne]

Interesting... you have a capacitor between the negative side of the coil and the frame? Is that shown in the FSM?

I find no mention of it in the FSM, but it does appear to be in the parts drawing, but has no separate number listed.

I tried disconnecting it, but the car was obviously not at all happy without it, missing and coughing badly even at idle.

Edited June 15, 2011 by Arne

[240dkw]

Arne: That's Odd, mine is on the positive side. The sticker on it reads "ncc nc-47ct-a2 150v.47m" I bought this car in a non-running state so I can not tell you if mine is correct.

Walter: There are a total of three on my car, + coil, points & voltage regulator.

Dan

[Arne]

My car has the same three, but the one at the coil has always been on the negative side to the best of my knowledge. It has the exact same label as yours, Dan. As I said, it doesn't like to run w/o it.

[Zed Head]

I have seen where people have attached the HEI module to the bottom of the distributor. Maybe this is an option for retaining the stock appearance, but getting the advantages of electronic ignition. It would require a ZX distributor with a VR, but might be worth the effort. The more I read of the HEI module's design and function, the more impressed I am. They really packed a lot of function and durability in to a small, simple package.

[240dkw]

Arne: I did some quick reading as to what the Capacitor/condenser (same thing) is for on the coil and it looks like it is used to boost the voltage of the primary windings. I wonder if the newer hi-output coil would work without it?

[Arne]

I wonder if the newer hi-output coil would work without it?

The Crane PS20 does not.

Did your reading confirm whether the negative or positive side?

Edited June 15, 2011 by Arne

[Zed Head]

I mis-wrote in my previous post. A 280Z distributor would give the VR, that would work with the GM HEI module, and more stock appearance without the big box of the ZX on the side.

My 280Z has an inline capacitor that runs back to ground at the distributor. I don't know where the other end goes. Otherwise the coil does not have one attached to either post, and nothing is shown in the wiring diagram for the ignition circuit. I think that for EMF noise reduction the capacitor just needs to be attached to the line that's being protected from the noise. But I don't think that the electronic ignition coil uses one because the "dwell" and coil charging is controlled by the ignition module.

And I just took a quick look at the ignition circuit in the Engine Electrical section for 1972 (because I need to know now) and it shows the condenser connected to coil (-) along with the points.

[Arne]

1.) I don't think trying yet a third type of EI is worth pursuing at this point. Both the Pertronix and ZX ignitions are well-known quantities and work fine on many (most?) 240Zs. Trying something else without discovering the root issue seems like a waste of time and money to me.

2.) My '71 FSM shows a single condenser connected to the points as well. But I can find no documentation on the OTHER condenser mounted with the coil. Since the car does not even want to run at all without the one at the coil, and both condensers appear to be original to the car (and therefore ~40 years old), I think it'd be prudent to replace them. If I could only find the one by the coil listed somewhere....

I still have to assume that I'm missing something here, something quite basic. So I'm going to leave the Crane coil in place for now and replace all the rest of the points ignition parts. I need to start fresh.

Edited June 15, 2011 by Arne

[240dkw]

Well, apparently the condenser/capacitor/whatever that connects to the negative terminal of the coil is a required part. The car will barely run w/o it. And since it is original, I'd like to replace it. It does not show separately in the factory parts book, appears to come only as part of the "Ignition coil assy." Any ideas on where to source the correct part?

Arne: I measured a couple of capacitors that I have and they are a .47 uF , so the part number ncc nc-47ct-a2 150v.47m equates to a 150V dc, .47 uF capacitor. (.47M, .47 uF, .47 micro Farad are all the same thing) If you want see if it is the cause of any of your problems you can this size of capacitor at any electronics store. It would not look correct, but will work for troubleshooting. As well, I was wrong about what the cap is used for. as near as I can tell, it is there for the reason you first eluded to, noise suppression for the radio. Which does not explain why it will not run without it? I dug through my part boxes and found 6 coils and 4 have it on the + terminal and 2 have it on the - terminal. Dan

[Arne]

Time for systematic testing.

Baseline config:

• Points (~12k miles)
  
• Condenser at dizzy (unknown age)
  
• Cap and rotor (~12k miles)
  
• Wires (~1k miles)
  
• NGK BP6ES-8 plugs, ~3k miles, great shape, 0.8mm gap (.032")
  
• Original coil
  
• Original resistor connected
  
• Original condensor at coil connected to negative terminal on coil
  
• Timing 5° BTDC (factory spec)
  
• Dwell angle 38° (factory spec 36-41°)
  

Results and notes:

• In this config, the car runs fine throughout the rev range.
  

Edited June 17, 2011 by Arne

[Arne]

Test #1

Changes from Baseline:

• Replaced original coil with Crane PS20 (1.4Ω)
  

Results and notes:

• With no changes other than the (presumably higher output) coil, the car runs as before until over 5000 RPM, where the spark appears to begin to break up and miss.
  
• Car will not run well at all if the condenser at the coil is disconnected. Hard to start, very bad idle, won't rev. Since I believe this condenser was intended only for radio noise suppression, this seems wrong to me.
  

Edited June 16, 2011 by Arne

[Arne]

Test #2

Changes from Baseline:

• Crane PS20 (1.4Ω) from Test #1
  
• Installed fresh points and condenser at dizzy
  
• Dwell angle 40°
  
• Disconnected condenser at coil
  

Results and notes:

• Car runs fine throughout the rev range again.
  
• Car would not even start with the coil condenser connected to negative terminal, but started immediately when I disconnected it. I wonder if the correct connection to suppress interference may be to the positive terminal of the coil. Connecting it to the negative terminal may have been a stopgap to compensate for a bad condenser at the dizzy?
  

Hmmm. I wonder if that condenser at the coil may have been the root cause of all my issues. I'm not going to jump the gun, will continue to step through this sytematically.

Edited June 16, 2011 by Arne