'72 240Z sudden engine stalling

[vtdds71]

I was unable to find a previous post on this issue, so I will try posting a new thread.  My '72 240Z has been suddenly stalling, sometimes within 5 minutes of driving, and other times after 40 minutes, or more.  It sometimes re-starts itself immediately (i.e. the engine just "stumbles" badly), and other times I have to crank the starter.  I have not ruled out a fuel-delivery issue, but I feel the issue is electrical, due to the suddenness of the episode, and the rapid recovery.  I had installed a Crane XR700 breakerless ignition system on the car, along with a Crane PS40 "performance" coil and new ballast resistor, about 5 years (and 4000 miles) ago.  The distributor cap, rotor, and all ignition wires are similarly "new".

 

When I removed the dizzy cap today, I found the center electrode inside to be completely deteriorated, and it no longer had any spring action downward to keep it in constant contact with the rotor.  I removed the center electrode, and found it to have worn down to maybe half its original length, and there was NO sign of a spring remaining above it, inside the center electrode receptacle.  I have attached a pic below showing what was left of the center electrode (on the left) next to the same electrode I removed from an older dizzy cap (on the right).  The rotor shows tracks of carbon deposits, and a roughened center contact spot.

 

Obviously, I will need a new dizzy cap and rotor, but I'm wondering what happened to cause this rapid deterioration of the center contact.  I've never before seen such dramatic wear inside a cap.  Does this indicate the XR700 is producing way too "hot" of a spark?  Maybe the dizzy cap was of poor quality from the beginning?  Could the ballast resistor be defective?  Or, maybe the PS40 coil is defective, as indicated by being hot to the touch while running?  If anyone has any thoughts or ideas, I'd really appreciate it.  I hate to install just a new cap and rotor, only to see this happen again in short order.  Thanks to all.

[NewZed]

The XR700 is just an electronic version of points.  That's why you still need the ballast resistor.  The PS40 has 1.4 ohms primary circuit resistance which is very close to the 1.5 to 1.7 ohm range of the stock coil.  Lower primary circuit resistance is how they "up" the performance, so yours is on the barely improved end of the performance range.  The coil should only be running hot if the new ballast resistor is lower resistance than the stock one.  Or if you wired it backward and have the resistance bypassed.

 

None of those should cause your distributor cap to self-destruct though.  Looks like you just got a low quality or defective distributor cap.  The current that passes through the cap is very short time frame and very high voltage.  They're designed to take huge voltage.  Your problem looks mechanical.

 

Good work though on the troubleshooting.  A new high quality cap should get you right back on the road.  Everything else looks pretty good.

[vtdds71]

Thanks for your feedback, NewZed.  I just checked the resistance on the "new" ballast resistor, and it measured 1.5-1.6 ohms, whereas the old ballast that came off the car years ago measured 1.8 ohms.  So, I guess this means there is a bit more juice hitting this coil than was sent to the previous coil.  I'm not sure how one can wire this resistor backward, to be honest.  Can't the leads be swapped, and still have the same resistance produced going to the coil?  Can this lower resistance cause the coil to overheat?  Basically, I've been using the ballast that came with the PS40 coil when it was new, so I assume it must be acceptable.

 

I'd like to believe that I just had a poorly-made distributor cap installed, but I can't help thinking there must be something else at play here.  It just seems very odd to me that the central electrode would literally burn up over time, especially since it has only been in place about 4000 miles altogether.  There is no sign of any burning on the individual six contacts sending the spark to each cylinder, but I know they are made of an entirely different material, too.  I've tried calling the Crane helpline, but that number is no longer valid.  Attempts to call Summit Racing, which pops up first on my Google search as a Crane supplier, have been met with a busy signal all day.  Somewhere, there has to be some technical person who is familiar with this equipment, and who can explain to me what is happening.

 

As an alternative, I've wondered if I could expect better luck if I switched over to a Pertronix Ignitor system altogether.  They seem to offer a Type I and a Type II that will fit the '72 Z.  And, they still seem to be in business, whereas Crane products have been taken over by someone else, and they seem to have renamed their products as FAST.  I would welcome any comments from anyone re: their experiences with any of these products.

[Miles]

Confirm that the connections on the ballast resistor, coil and distributor are clean and snug.

[NewZed]

23 hours ago, vtdds71 said:

When I removed the dizzy cap today, I found the center electrode inside to be completely deteriorated, and it no longer had any spring action downward to keep it in constant contact with the rotor

 

If the spring was bad or stuck the coil spark would have been jumping the gap all of this time.  That would cause more heat and ozone and wear on the electrodes.

 

My mistake on the ballast resistor.  Later cars have an extra terminal to bypass the resistor for hotter spark.  Apparently 1972 does not.

 

Since the engine's not blowing up your best option might be to just buy two of a higher quality cap and keep the extra in the car as a spare.  Good luck.

[vtdds71]

What amazed me was that the spring above the carbon electrode in the center of the distributor cap had completely disappeared!  When I pushed up on what was left of the electrode, it just went up inside the center receptacle, and stayed there!  I was able to knock out what was left of the carbon element, but there was no sign of a spring left.  Pretty amazing that I was even able to start and drive the car, given this level of deterioration.  I would say that this entire Crane system has less than 3000 miles on it.

 

In Googling around the internet, I came across an article and video that discussed the importance of getting near-perfect "phasing" of the optical disc of the system.  Apparently, if it isn't perfectly adjusted relative to the spark plug wire contact, it can force the system to generate a hotter spark (?) in order to leap across the wider air gap between the rotor tip and the plug wire contact, and this can generate more internal heat, and wear.  I thought I had adjusted the trigger mechanism exactly as described in the Crane instructions, but maybe not.  Some have talked about drilling a "viewing hole" into the top of an older dist. cap so that you can see exactly what kind of spark transfer is occurring as the engine runs, distributor mechanically advances back and forth, etc.  Does this sound plausible?

 

The new cap and rotor have been ordered, and will arrive soon.  But, I guess there remains the question of parts quality, too.  So much aftermarket stuff seems to be coming from low-cost Asian sources that you have to wonder just how good any of this stuff really is.  Even parts bought through reputable sources stateside seem of questionable origin in many cases.  And, when I've called some of them lately to ask about the products they have sold me in the past, they oftentimes take the attitude that "We don't know.  We just sell parts here".  Not encouraging.

 

Thanks for any further thoughts or ideas that anyone may have to offer.