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The 'Prince" has struck

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Jim_Newman

Jim_Newman

Jedi Hopeful
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The 'Prince" has struck

Hi Gang:
This one is for the automotive electrically unimpaired in the group (of which I not a member).
The BN7 will not start. There is no spark at the plugs. Every electrical component (lights, horns, wipers, starter motor, etc.) works fine. In the process of trying to diagnose the problem, I removed the distributor cap(new) and disconnected the high tension wire to the coil(new). When I turn the ignition switch OFF, a lovely hot spark jumps from the centre post of the coil to the nearest ground. This happens each time I turn the switch on then off.
I have checked the continuity of wires wherever I can, have checked the connections under the dash, and scratched my head quite a bit.
Can somebody pleeeease tell me what is going on. I assume there must be a short somewhere, or something that should be grounded isn't but how do I find what and where it is and fix it. The car was converted to negative ground years ago and has a Pertronix ignitor set up.
As always, any help or guidance is greatly appreciated
 
Re: The 'Prince" has struck

Spark when energising then de-energising means coil works, power to coil is correct.
Now.
What did you change last?
Points or some other system?

If points, did you just change anything, and get the ground isolators wrong?

If not, we could have a bad condensor or points closed. Crank the engine with cap and rotor off, watch the points, do they open and close?

Questions, and something to check.
 
Re: The 'Prince" has struck

No points, no coil, Pertronix ignitor.
 
Re: The 'Prince" has struck

The usual reason for not having spark at the plugs when you have it at the coil is a bad rotor or cap. If you have spark at some plugs, but not all, it would be a bad spark plug wire or bad cap.

Some rotors have had high failure rates.

I have also heard that installing the Pertronix disk under the rotor pushes the rotor up so that the carbon brush in the center of the cap is crushed.
 
Re: The 'Prince" has struck

Thanks John
I had not considered the rotor itself. I'll check it out tomorrow. The carbon brush was duly ground down in order to fit properly over the rotor and it makes good contact with the rotor.
Cheers
 
Re: The 'Prince" has struck

There are only a few components between the disti cap and the plugs.

I would check the cap, rotor and if any doubt, simply replace. Next check the connections to the pertronix. If it still doesn't start, run a jumper from the battery to the +12V line (I'm looking at the pertronix trouble shooting guide from the one I recently installed), as the pertronix will not operate with a low voltage condition. If all that fails, I would bet on the pertronix unit went south.
 
Re: The 'Prince" has struck

There should have been no reason to grind the center brush down unless the magnet assembly is not fully seated.Remove it and try a different location to install it on the cam>-Fwiw--Keoke
 
Re: The 'Prince" has struck

If you've got a Pertronix and there's a spark on switch on or off, but t no other time, it is probably faulty. Try another.

Ash
 
Re: The 'Prince" has struck

The rotor seems OK. The concensus is a faulty Pertronix. Before buying a new one, is there some independent test I could run on the Ignitor unit itself to verify that it is indeed defective? This whole process started when the engine fired up and then quit after 20seconds and hasn't run since.
Happy Thanksgiving to all our US friends.
Cheers
 
Re: The 'Prince" has struck

I will do that t.h., but I'm getting this spark to ground from the coil when the rotor is out of the game. That is, the high tension wire to the distributor is disconnected. The only connection to the coil are the usual low tension wires plus the black and red wires from the Pertronix unit. Since the coil is producing this high energy spark, it appears to be receiving the required 12V. What I'm having the most trouble understanding is why the coil discharges this way (right to the ground terminal on the coil)when the ignition is turned OFF.
Cheers
 
Re: The 'Prince" has struck

Did your check/replace the cap and rotor? A quick google (not mine, but makes sense knowing how it operates) netted this to test your pertronix with a simple multi-meter.

Connect a wire from the ignitor base plate to the battery earth terminal; Connect the red wire from the ignitor to the battery live terminal; Connect the -ve wire from a multimeter/voltmeter to the ignitor black wire; Connect the +ve wire from the multimeter/voltmeter to the ignitor red wire; Turn or briefly crank the engine to rotate the magnetic sleeve - volts should fluctuate between battery voltage and 0v; Constant voltage indicates the ignitor is faulty.
 
Re: The 'Prince" has struck

yeah, I would replace your cap and rotor before fiddling with the pertronix. The Pertronix units are far more reliable than the rotors especially. I always carry spare rotors in my cars.
 
Re: The 'Prince" has struck

I had a Pertronix installed in my bj8. I got soon problem with ignition. When investigating I found out that the center plasic part over the cam lifts the rotor from its original position and distributor cap connector seat to rotor gets damaged. By grinding the lower face of the rotor this lift can be compensated. Measure the installation height of the rotor to a reference point of distributor house, with and without the center part of Pertronox to eliminate same problem.
 
Re: The 'Prince" has struck

For my TR6 the frist Pertronix failed and would discharge a spark each time the ignition switch was cycled on and off. The second Pertronix failed when the magnets seperated from the mounting on the point cam. I understand the later Petronix ignitions are improved but after being twice bitten...

After the second failure with the Petronix ignition I installed a Crane Fireball with the optical sensor trigger. That was about fourteen years ago and have not had ignition failure issues since.
 
Re: The 'Prince" has struck

You're absolutely correct Bustren. The alternative approach is to grind down the carbon element at the centre of the distributor cap above the rotor (which is what I did) to compensate for this mismatch.
Cheers
 
Re: The 'Prince" has struck

One spark from a Pertronix on shut-off is generally a sign of failure. That would be my initial guess on diagnosis, and I deal with these problems daily.

I find that RFI noise from the solid core spark plug wires in the AH 3000 will actually wreak havoc with the Pertronix ignitions. RFI can actually "blind" from the module reading its own magnetic signal if there is a lot of noise from the solid core ignition wires. later BJ8 distributors can run modern carbon-core wires which eliminate the problem. If you use carbon core wires in the 3000's DM6 distributor, The wires will fail relatively quickly from puncturing them with the hold-down screws.
 
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