I started a short drive, in one mile I noticed the tachometer was bouncing around, especially on acceleration. At four miles I hear a lot of backfiring on engine braking. I stopped at an intersection, then the engine cut out and couldn't be restarted.

I had full pressure, but no spark. It was flatbedded back home and now the fun begins.

I'm confused where to start since the ignition has undergone an electronic upgrade using a Mallory coil and distributor. There are two ballast resistors one with three contacts and the one with two contact just below it. One wire from the upper (three contact) resistor connects to the lower resistor. The other end of the lower resistor connects to the positive side of the coil. The resistance across the lower resistor is 1.7 ohms.  With the ignition on, I get 3.3 volts to the coil from the ballast resistor. 

I think the resistance is high and the voltage low (then again, what do I know) so I'm wondering if there is a problem with one or both resistors. I am also confused if a ballast resistor(s) is even needed with an electronic distributor.

I was hoping to get in one more Solo event this year, so please point me in the right direction.

Jeff

260z with many old performance upgrades.

280 engine/5-sp transmission

Edit - plus I think that you're measuring voltage incorrectly for what you're trying to do.  But still, there should be no voltage drop unless current is flowing.

Voltage should be battery voltage unless current is flowing.  There shouldn't be any current flowing unless the engine is running.  3.3 volts implies that your ignition module is shorted out.  The bouncing tach needle is another sign.

There are some threads on the site about the Unilite modules.  You can get replacements.  And here is a test procedure for the Unilite.  Not exactly your model but they're all the same.

http://documents.holley.com/605_v2.pdf

Edited September 24, 20186 yr by Zed Head

Thanks for the input. Am I correct in my understanding that the ignition module and coil are one in the same?

The ignition module is under the distributor cap.  The coil would be the cylindrical object with two wires attached, and a center wire that attaches to the distributor cap.

This is a coil.

Actually, I just read the Unilite instructions, and depending on where your probes were placed and how fast you moved, you might have been close to the proper test procedure.  I think that the module times out after a short time though, so you have to have it open as shown, and use the optics blocking technique to get consistent results.

To elaborate on Zed Head's response on coil vs ignition module, the coil is an energy storage device/transformer. It can take 9 (ballast resistor present) or 14 (operating voltage when the alternator is turning) volts DC and step it up to 20,000 to 40,000 volts DC depending upon the number of windings in the coil. The lower voltage side of the coil is an open circuit. The negative post has no direct path to ground. This is where the ignition module comes in. The ignition module detects the position of the distributor, usually with an optical trigger or magnetic reluctor. At the appropriate time, the ignition module closes the path to ground for the coil. With the completed path to ground, you have current flow through the low voltage side of the coil and a spark at the spark plug.

 It’s beginning to come back to me from my auto shop class in the early 1970s when only Chrysler had pointless ignitions  

 When the breaker points open or in this case When the  electronic switch  opens the circuit, that cuts the power to the coil causing the magnetic field to collapse and generate a very high voltage. 

 I think we used to observe this on a Sun oscilloscope in auto class.  

Craigs list has a Snap On oscilloscope for $150 nearby me that I’m tempted to get but I’m not too sure I can figure out how to use it. 

That's right.  The test described in that pdf file I linked to will tell you a lot though, for much less money than a $150 scope..

Can you take a picture of your distributor and engine bay?  Might be some clues there.

 

Coincidentally, one of the old Unilite threads just popped back up.  It's a floater.

https://www.classiczcars.com/forums/topic/60072-misfiring-while-cruising/?page=2

I ran through the Unilite test procedure and

There is 12 volts coming off the negative side of the coil.

The voltage drops drops to 1 volt when a card blocks the LED.

I think that means the ignition module is working.

I remember that thread. I commented on it related to the availability of the Mallory cap and rotor.

I've attached photographs of the distributor with the cap/rotor removed, the cap & rotor to show their condition, and the coil.

 

 

Edited September 25, 20186 yr by Jeff Berk

Just going through the basics, the next question might be "why would a functioning module not create a spark?".  Does the distributor shaft turn when you crank the engine?  Does the bottom of the rotor have the optics blocking part intact?  Was there anything loose under the cap when you took it apart that might have been blocking the optics?

Another common ignition module problem is that they overheat, fail, then come back to life when they cool down.  You might find that the engine starts now if you put it all back together.  Your testing shows that it should work.

Edit - forgot to say...other parts can overheat also.  Coils, wire connections, maybe the ballast resistor.  If it starts then dies again you'll be farther down the troubleshooting path.

 

Edited September 25, 20186 yr by Zed Head