Triumph Repair: 77 Spitfire Ignition problem, ballast resistor, answer mark

Question
QUESTION: Hi Jim,
  I have been chasing sparks on my 77 Spit for a while.  I'll break this down to make it easier to diagnose or confirm my suspicions. 45DE4 Dist and Piranha Electronic Ignition Box(probably from dealership).New Accel 8140 12volt coil(problem existed before changing to new coil).

All ground connections have been cleaned and tightened.

Problem: Car just quits without warning.  Loses spark at coil. Tach drops to 0 and engine just shuts off.

Test 1:
  Coil + hooked to ignition -- 6.06 volts
  Coil - hooked to ground on engine -- .25 volts

Test 2:
  Coil + hooked to ignition -- 12.45 volts
  Coil - not connected -- 12.43 volts

Test 3:
  Coil + hooked to ignition -- 6.57 volts
  Coil - hooked to Piranha box -- 1.21 volts

Test 4: Cranking Test
  Coil + hooked to ignition -- 12 - 13 volts
  Coil - hooked to Piranha box -- 2.5 - 3.5 volts

Test 5: Running Test
  Coil + hooked to ignition -- 8.3 volts
  Coil - hooked to Piranha box -- 3.35 volts

 What I have found out is that when the engine quits that the voltage on the coil negative goes from 1.2 ignition on to 12 volts ignition on.  
 I also noticed that while the coil negative is disconnected, the volts are 12 or more but when you connect the Piranha that it volts drop to 1.2 volts.

  So my assumption is that the Piranha box is starting to go bad.

  And I have one question: Should change the coil back to a 6 volts coil?

Thanks for you help,
Mark

ANSWER: Mark,

There should a ballast resistor in the system.  Typically they were mounted near the alternator at the lower back bracket.   If so, you should definitely be running with a 6V coil, not the 12V coil.  That may be one problem.

It's possible the Piranha unit is going bad, but typically with the electronic setups they either work or they're dead.  

A slight possiblility is that something in the electronics pack is heating up and causing a connection to be broken.  Once it cools down it works again.

Another good idea is to look into the wiring, especially the lead for the tachometer.  If it's shorting out inside the dash area it'll also kill the engine.

And with a 30 year old car, it's not a bad idea to give the rest of the wiring a good look over too.  A loose or corroded connector can also give intermittant problems.


Cheers,

Jim

---------- FOLLOW-UP ----------

QUESTION: The ballast resistor is located on the back on the alternator but it is no longer used. From what I understand the Lucas electronic ignition systems from the factory where junk and where replaced with the Piranha or Allison system by warranty.  When they did this they bypassed the ballast resistor but according to the website a lot of the mechanics left them in place(lazy I guess)such is the case here.  With that being out of the loop do I still need a 6v coil or will the 12v be okay to use?
Lastly, the firing problem doesn't happen just when it has been running. I have had it sit overnight and then not fire or have driven it 200 miles and then have it not fire.  Sometimes I can drive down the road and have it quit and then coast a bit and then sputter back to life.  This is really weird.  I have traced all wires and checked all grounds. I'll keep looking and if you don't mind keep running it through your head.
 The part that gets me is that when it quits, the voltage on the negative side jumps from 1.2 volts up to 12 or more.  When I see this I know it want crank. I keep trying everything and moving wires and such until I see 1.2 volts and then it fires right off.
 Oh well, when I get this one figured out it will be one for the books.
Thanks again and I look forward to hearing from you about the 6v or 12v coil.

Answer
Mark,

The electronic ignition unit replaced the points in the old style ignition setup.  In the points setup, with the points closed the negative side of the coil is grounded and charge builds up in the coil.  When the points open, the charge is released via the high tension lead to the distributor.

All the electronic unit is doing is replacing the points with a transistor, eliminating the need to clean/adjust the points every couple of months as used to be the case.

When you see 12V at the negative side of the coil its the equivalent of having the points "open".  If you have an old needle type voltmeter you could probably crank the car and watch the needle jump as the Piranha unit goes through it's cycles of "open" and "closed".

I'll be honest and admit that when the Lucas unit finally died on my '78 Spitfire I went back to a points distributor.   

As to the coil, I'll take a peek at the Piranha website to see if they recommend a change on the coil.  

Cheers,

Jim