No Spark...

[kjohnson2444]

OK. I'm stumped and I have searched the forums and and tried everything that I've found, but I cannot get my car to start. It is a 1970 240z with the stock ignition. I recently pulled it into the garage, running rough, shut it off, and now it won't start. I first checked for spark at the plug, but there was no spark, so I checked at the main wire from the ignition coil. No spark there either. I do have 12v to the coil when the car is switched on and when cranking. BTW, it cranks over strongly. I have replaced the coil, points, condenser, ballast resistor, rotor, wires, and plugs. (Not the distributor cap. Couldn't find one locally.) I even purchased a second coil in the event I had a bad one out of the box. No luck. With power to the coil, I don't understand why I would not get a spark out of the coil. Any thoughts?

[beermanpete]

You verified half of the circuit, how about the other half? Ground, that is.

Is there voltage at the negative side of the coil when the points are open? Does the voltage fall to 0 when the points close? Can you see any arcing across the points while cranking the engine?

The ground path for the coil is through the negative coil wire to the distributor, feed-though terminal, lead wire moving point contact, stationary point contact, points mounting frame, mounting screws, advance plate, ground wire, more screws, distributor body, and then the engine block. To much dirt or corrosion (or over zealous painting) at any of the connection points could prevent a good ground connection. Check the wires for loose or damaged terminal, broken conductors inside the insulation and cracked or worn insulation. Replace or repair as needed.

[robftw]

Check the terminal under the coil, my one wire was broken inside the rubber caps and was giving me the same problems. Also check your grounds, that was my 2nd problem

[kjohnson2444]

Thanks guys. Knowing the complete ground path was helpful, and I did not know that when the points were closed I should get 12v to the negative terminal of the coil. I discovered that I was getting 12 volts to the negative terminal continually. I watched the points and they never closed! I adjusted the gap all the way down to get it closed (there is no more adjustment possible). Put the rotor and cap back on, and bingo! The car started on the first tap of the starter and purred like a kitten. I guess I should have been more careful when I replaced those points.