67 Barracuda Ignition Issue
Here are some of my amateur electrician observations:
1. The 12.5 volts at all 4 poles of the ballast seems correct. Guessing the top 2 poles would likely drop due to the ballast once current is applied.
No it is not correct, if the system is connected.
DO NOT troubleshoot willy nilly. When you make measurements with connectors separated, you can lead yourself down "the path." Taking a measurement is useless if you don't know what it means.
Start at the coil. Turn key to run, take a voltmeter reading from coil + to ground. That reading SHOULD be somewhere between 6 and maybe 10V. THAT IS BECAUSE the key provides power to one side of the ballast, through the ballast, through the coil, and then the coil NEG is grounded through the box circuitry and the BOX GROUND meaning the BOX CASE. That is your current functional path
THE CURRENT through the coil DROPS the ballast voltage which is why the coil should read BELOW battery. That is "normal."
If that reading is quite high, AKA near battery, it means the box is ungrounded, the box is bad, the box connector is iffy, the coil is bad, or a loose / bad connection in that path.
The box MUST BE GROUNDED. Unbolt, clean, scrape, use star lock washers
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Start/ crank/ ballast bypass function:
When you crank the engine WITH THE KEY (and not jumpering the starter relay) you have an entirely DIFFERENT setup. Now you have the IGN2 circuit from the key in play. This is a separate contact in the ignition switch designed to bypass the ballast for starting, to give a good hot spark. BUT IT IS A TRICK
Clip meter to coil and ground, crank engine WITH KEY, and take reading. Coil + should be at or near "same as battery."
The RUN LINE GOES DEAD during cranking. HOW DOES the box get power for starting? The power from the coil + bypass circuit BACKFEEDS through the resistor and to the box, meaning, yes, you got it, the box sees LOW voltage during start. Don't ask me, I did not design it.
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Separate distributor connector. "Rig" a spark gap at coil tower USING A PIECE OF WIRE, and NOT the coil radio resistive wire. Rig the gap to 3/8 or so, and take the engine bay side of the distributor connector. "Tap" the exposed terminal to ground and each time you do that, should produce one single "snap" hot blue spark
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Pull distributor cap. Examine for carbon tracking junk, water, etc, and examine pickup and rotor for excessive rust, debri, and strike damage. "Feel" for shaft play. Consider checking reluctor to pickup gap
Check distributor pickup for continuity. There is some argument as to acceptable resistance readings. If it is continuous, that is good.
BE VERY SUSPICIOUS of the distributor connector. Examine for corrosion, "work" in/ out several times to scrub the terminals. I sometimes use a .177 caliber brass rifle brush to clean the female terminals.
Attach your voltmeter to the dist. connector on low AC (NOT DC) volts. Crank engine, and dist. pickup should produce about 1V AC
Check the box connector. Examine for corrosion, "work" in/ out several times to scrub connections.
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INTERMITTENTS Maybe I don't have to tell you this, but they are the MOST difficult. I HATE THROWING MONEY at a problem, but intermittents are different. Sometimes you just have to close your eyes and gamble.