Technical Why no or weak spark?

What am I doing wrong on his old little Willy four banger? This one has me stumped.
The key is just a new universal switch (tested and good). The distributor has a Pertronix (which is new and tested), the coil is the correct ohm rating for the application (3.0), no ballast needed with coil. I think maybe it is voltage drop at cranking, but not really sure. Battery is fully charged. Wiring is all new. I don't think I really need that jumper from the I on the solenoid, but don't think it is hurting. Help!

 

As for suspected voltage drop while cranking. Did you also test solenoid to see if by pass is working?

 

As Johnny Gee says, that "I" terminal is designed to provide full 12 volts and bypass the ballast resistor if you have one in place. That should provide whatever battery voltage is available while cranking as it also bypasses the ignition switch as well. I have always used a lower resistance coil with a ballast resistor just so I could get the hotter spark while cranking, just make sure the pertronix unit is getting full 12 volts and the red wire is not being fed by the ballast resistance wire. I have seen many times the ballast resistor is in the "IGN" wire (correct) and the red wire from the pertronix will be connected to the coil + after the ballast resistor (incorrect) and cause issues.

 

You need to see what your battery voltage is while cranking. A starter that draws too much current will lower battery voltage enough to make the ignition system weak or no spark at all.

Have you got NO SPARK or WEAK SPARK?

 

I am not getting spark but on one attempted start it did backfire out the exhaust which leads me to believe I have some sort of fire (spark).
I am getting 10.4 at the positive on the coil at cranking, but nothing on - side.
Battery is 12.7 at rest.

 

Did you have the Pertronic system before this issue?

 

Seems the OP is basing weak/no spark off of a backfire and the engine not starting. Timing might be the issue.
I’d verify spark or lack of it, from the coil wire and work from there.

 

Only told it ran before, but that was sometime ago. With points, different electrical wiring, and fuel tanks.
95% sure it is a spark issue.

 

Cleaning solenoid base now. Ground may be suspect.

 

I’m guessing you don’t have a timing light? If not, pull the coil wire from the cap, slide the boot back and have someone try to start it while you hold the end of the wire about 1/4inch from the block. See if it jumps spark from the wire to the engine block/head.

 

Yeah, my light is broken, but I checked by hand. Nada.

 

Assuming the coil is good, and based on the info no spark from the coil, I’d suspect the conversion is the issue. I’ve never worked on a conversion before, so have to bow out now.
Good luck!

 

I ohm'd out the resistance on the coil primary and secondary and that checked out. Pertronix bench test is good too. I think it is my wiring somehow or weird resistance somewhere. I don't know.

 

Did I read that right.... you have 10.4v cranking but none with just key on?

 

Key on I have 12.7 at the + on the coil, but nothing on - side.
Cranking it goes down to 10.4 at + on coil, but still nothing on - side.

 

It also backfired when I keyed off, if that has something that might shine some light.

 

You do not use the I terminal on your solenoid with elecronic ignition. Whatever voltage is going to your ignition when the car is running is what it gets while cranking. The ignition circuit built into your solenoid is to offer 12V to the ignition when cranking a points ignition which does not normally run on 12V. A 6V vehicle does not use this cranking system.

If you are getting a major voltage drop to the ignition system when cranking I am going to suggest that you have a wiring problem or a problem with your starter or your battery does not supply enough cranking amps for your application. Lots of things to check here.

First off dump the I circuit and then crank it. Check your voltage to the line side of the coil (normally the + side on a 12v ignition system). If you are suffereing a major voltage drop while cranking then start trouble shooting your electrical system.

 

The only reason I brought up by pass is because I'm unsure if OP has his terminals correct. What if he's on ACC (which is not shown) instead? Never seen a universal switch without 4 terminals.

 

Thanks guys. Wondering if the problem is in the main battery wires.
I'll ditch the I term. I didn't think I would be using it.
Ignition switch does have ACC too. I just forgot to put that in the crude drawing. The Coil + line is coming from the IGN on the ignition switch.

 

This system was converted to 12 volt with a GM alternator, but it still has the big boy 6V starter, which I heard is not an issue, but maybe it is drawing too much.

 

The 6V starter running at higher voltage should not be a problem at all. Your lower voltage uses more amps to turn an electric motor. When you up the voltage the amp draw should change accordingly. of course the old starter could be worn out that is also an option.

 

That sounds correct you have good cranking voltage and a good battery. The fact that you read zero volts on the - terminal means that the coil is being grounded by the pertronix unit.

The only things causing a weak or no spark would be the coil itself, or a bad pertronix unit. The pertronix unit has to turn the coil primary off to get a spark in the secondary. If it doesn't do that or doesn't do that well you get a weak/no spark.

 

Also, if you didn't have a good ground for the pertronix unit, the - post would read a voltage. The zero reading means that your distributor ground is good.

 

The backfire when turning the key off sort of illustrates that the pertronix unit isn't turning the coil off like it should. Turning the key off shut off the current in the coil primary winding causing a high voltage in the secondary. I sparked a plug when you did that causing your backfire.

 

So here’s something to think about. Was the Willys originally 6 volt and was it positive or negative ground? Did you purchase a conversion unit for the original application that may not now be correct for a 12 neg(assume) ground system?

 

When cranking you should see a "pulsing" voltage on the - side of the coil, as the Pertronix charges and discharges the coil.

 

Do this test again with the Dist - side of the coil disconnected.
And ground the multimeter [or use a test light]

This will test for voltage through the primary windings

 

It should be negative ground. My 48 CJ2A has run and cranked fine with the original points distributor for 73 years. Mine is 12 volt changeover with original 6 volt starter. Grinding on the starter too long will toast it.

 

Unless you have a graphing meter, I don't think you will see the pulses. The pulses happen pretty rapidly and DVOM's tend to average everything. A scope would be a great way to see this.

 

But would a conversion based on a 6v system work on the 12 volt? Not arguing just speculating.