Intermittent spark is a symptom of?

[gbhumphrey]

Hi, again on my 1971 911E. I get no spark off the coil when I turn the key, but get ONE spark when the key is released. Anyone have any idea what this means? bad coil? It was replaced as well as the ignition control unit 2 years ago. It looks old, the work order ( always keep your receipts and work orders!) says it's new, so it they have bamboozled me and now it's just worn out.
So, the problem, no spark off the coil when I turn the key, but get ONE spark when the key is released. Any ideas?

thanks

[JohnJL]

Hows your battery strength? I saw a similar result when I had a weak battery, it didnt have enough juice to spark AND turn the starter at the same time so I'd only get a spark when the motor was turning but the starter was off.

Try charging up your battery fully and cleaning all your plugs.

[tctnd]

That is normal. When you turn it on current flows through the coils primary windings and creates a magnetic field. When you turn it off the field collapses and induction into the secondary (high voltage) windings discharges across the plug gap. When the engine is running the points close then open (3 times per rev) providing ignition. If the engine happens to have come to rest with the points in the open position, switching the key on and off will have no effect.
regards,
Phil

[gbhumphrey]

So how do I test for spark coming out of the coil then?
When I turn the key, the ignition is on, the starter motor is going, the fuel is pumping. Isn't the rotor shaft turning, opening and closing the point?
I had been disconnecting the lead from the coil to the distributor cap and holding near the block, looking for a spark to jump.
Should'nt I be getting !SPARK!, !SPARK!, !SPARK! coming out of the coil as the engine cranks?

[tctnd]

Sounds like the coil might be grounded all the time. Be sure the points are opening and the coil to point wire is not shorted to ground.
regards,
Phil

[T77911S]

Originally Posted by gbhumphrey

So how do I test for spark coming out of the coil then?
When I turn the key, the ignition is on, the starter motor is going, the fuel is pumping. Isn't the rotor shaft turning, opening and closing the point?
I had been disconnecting the lead from the coil to the distributor cap and holding near the block, looking for a spark to jump.
Should'nt I be getting !SPARK!, !SPARK!, !SPARK! coming out of the coil as the engine cranks?

WOW. be thankfull it is not working. that will knock you on your a$$. i got hit by mine once, one of THE worst shocks o have ever gotten.
its better to either use and old good plug, connect it to a plug wire and lay it against the motor, have someone start the car and watch for the spark. or, use a timing light connected to one of the plug wires.
make sure cap and rotor are good and points are set to correct gap first.

[gbhumphrey]

Thanks but that didnt answer my question.
Should'nt I be getting !SPARK!, !SPARK!, !SPARK! coming out of the coil as the engine cranks?

[jmohn]

Originally Posted by gbhumphrey

Thanks but that didnt answer my question.
Should'nt I be getting !SPARK!, !SPARK!, !SPARK! coming out of the coil as the engine cranks?

At first I said YES, but I re-read your description of what your doing and the answer is No, if your really trying to get a spark jump from just the coil/dist. cap wire. Properly re-connect that portion of the system and check for the "spark, spark, spark" at a spark plug wire (use an old plug as described previously).

Jerry M
'78 SC

[ischmitz]

Correct me if I am wrong: The 71 uses a CDI ignition (Bosch). It is the dull silver box on the relay panel with the cooling fins. If that is the case your box is likely damaged. It probably charges up the coil and makes it act like a Kettering ignition. Be carefull. If the box is damaged it can put out a steady 400V at the coil terminal and that will do damage to YOU if you touch it. Be really careful.

It is NOT normal to get one spark with a CDI ignition since the coil is used as a tranformer. A traditional Kettering ignition uses the coil as a means to store energy. That is why you might see one spark when you turn off the key (points closed).

And as others said best use an old spark plug when testing for spark. Else wear a thick leather glove when handling the spark wire or you can get a nasty shock. The shock of a secondary ignition system is very unpleasant to say the least. Somehow like getting tasered (not that I know how that feels). However, it is of very short duration and only makes your heart rate go up

But the 400 volts out of a damaged CDI unit are outright life-threatening. Do not touch the primary of the ignition coil while the ignition is on and the box is whining. It can be very dangerous.

[T77911S]

Originally Posted by gbhumphrey

Thanks but that didnt answer my question.
Should'nt I be getting !SPARK!, !SPARK!, !SPARK! coming out of the coil as the engine cranks?

yes you are. but your last post asked how to test for spark coming out of the coil.

but i just noticed something. you asked if the rotor shaft sould be turning and the answer to that one is yes. check to make sure the dizzy is properly seated. check that the points open and close. check the wire from the points to the CD unit. it sounds like you may jusrt be missing the trigger from the points to fire the CD unit.

[gbhumphrey]

YEah I had done all that. I'll double check the wiring from the distro to the cd unit. If the PermaTune (2 years old) CD unit was bad would I get any spark? I'm really only get ONE spark, not a consistent pulse. I came across some other posts from people with seemingly the same issue. Many blamed it on the PermaTune. I'm not quite ready to believe that's the culprit yet. Well, I am, my wallet isn't.

[ischmitz]

Unfortunately, Permatunes have a less than stellar track record when it comes to reliability. And to add insult to this some are fully filled with epoxy and not serviceable. This is why many recommend a Bosch as the better alternative.

I think your unit might be the culprit. And as I explained if it is shorted it will energize the coil just like in a Kettering ignition. And when you switch the ignition key off the collapsing field in the coil gives you exactly one spark regardless of where the dizzy is.

Ingo

[T77911S]

permatune, go get an MSD.

[gbhumphrey]

OK, so, i'd like to take the PermaTune unit and coil out of the car and test them. Does anyone know of any instruction on this?