Troubleshooting and notes

Had another failure out of the blue with the same symptoms.  I verified the ERS was closing the relay and when closed manually you could hear the pump running. Use a spark tool to verify no spark at the plug or into the distributor.

When i got it towed home it was still failing.  I saw low voltage on the coil and no spark. I replaced the DuraSpark but it failed again later in the day. Need to go through the wiring in detail now that I'm home. I saw 4.5V on the coil in run which is wrong but I'm second guessing myself.  Suspecting the resistor or ignition is bad since i should see closer to 10v during run and 12v at start (I saw 12V at start).

I've spent some time looking over the wiring diagrams and will go poke at them again this weekend.  I suspecting the resistor is bad but that doesn't really explain why it doesn't start,  it would explain why it won't run.  

I put my spark gauge on the coil output so I know its not the distributor at fault but I did notice the arm and contacts are corroded so i figured I would replace it anyway. The most expensive part was the f@$# tariff to get it from the UK (thanks DJT).  I don't see any cracks in the plastic which I've heard is an issue for others.

10/8/25

I've still not found an obvious issue.  I was expecting to see ~10V on the coil when the key is on but I see 4.2v unless the engine is running than i see fluctuating around 10v.

I've been wondering if my coil or resistor is failing so I purchased a new coil and resistor.  I took voltage measurements before and after and the voltage went up a bit.  I was seeing 4.2V with the engine off and now i see 5.6v.  I measured it jumping around with the old (i dont know what) and 10.4v with the new when the engine is running.  I saw 12V during start on both.  I also measured the voltage at the original ballast resistor. When open I see 11.7V coming from the ignition relay (via fuse2?) with the resistor removed.  With the resistor in I see 10.8V on one side and 6.3V on the other. 

I found a post on piston heads (https://www.pistonheads.com/gassing/topic.asp?h=0&f=12&t=17926) pointing to 8203 coil as a replacement but I'm getting second thoughts after installing it since I'm noticing that its It's 45kv vs 40kv, and has less resistance than the old one.   It comes with a new resistor so swapped that too since i figured they need to go together.  https://www.jegs.com/i/MSD-Ignition/121/8203/10002/-1

Alternate coil specs

Duraspark module ECM

How to Test Your DuraSpark II Ignition System Parts With a Volt / Ohm Meter

The DuraSpark II Stock System Parts

Note that the only differance in 4, 6, or V8 engine's DuraSpark II parts are mainly the just the Distributor that is engine specific, plus it's Cap, Rotor, and Spark Plug Wire Set most all the other ignition system parts used are usually the same. I.E. The Coil and Blue Strain Relief ICM, Wire harness is the same except it might be longer for a Inline Six over that used on a 4 or V8 engine.

1. First thing is to test is the condition of the battery and its charge, clean the battery posts and the cable terminals. The battery charge needs to be at least 12.5 volts (Write down your voltage reading result for reference) if its not at minimum voltage then try charging the battery up and retest. Now you need to do a cranking voltage test on the battery (again Write this result down for reference), if when your cranking the engine over the battery voltage drops to less than 9 volts the battery will need to be replaced. Again these are the first things to do and is very important to check out that the battery voltage is at the minimum voltage or higher, plus the battery cables condition, cleanliness of all of their connections at each end and need they need to be tight before you can accurately do any other voltage reading tests.

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2. The voltage to the ignition coil positive terminal should be at the same voltage reading as when your were cranking the engine over. If its not then clean any corrosion, repair or replace damaged wire coming from the ignition switch (Usually this was a Pink Wire for many years), or if there's no damage then it’s time to replace that worn out ignition switch if you get a lower voltage reading. Next with the power switched off use your Volt / Ohm Meter to test the DS II coils primary resistance at its two terminals. Replace the ignition coil if this reading exceeds 3 ohms resistance.​

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3. Next with your Volt / Ohm Meter check the resistance of the distributors pickup coil with the ignition switch Off, by unplugging the distributor from its wire harness. Test the pickup coil resistance between the two parallel blades of the distributor plug, According to wsa111 (see below post). The resistance in the pickup coil should be in the 400-800 range. Most check out close to 600. If not than you will need to replace the pick up coil. Also test the resistance between each of the two parallel blades in the distributor plug (one at a time) together with the single perpendicular blade. Replace the pickup coil if its reading is below 70,000 ohms.​

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4. Plug back in the distributor wire harness again, test the cranking voltage to the ICM (Ignition Control Module). Probe the White wire to read its voltage at the ICM while you are cranking the engine over. If the voltage is weak (below the cranking voltage) or there isn't any voltage at all, examine the White wire for any type looseness at terminal connections, clean any corrosion, check for any external wire damage, or internal wire breaks from the starter solenoids S terminal and repair as needed. If the White wire checks out as in good condition then you will need to replace the starter solenoid.​

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5. Next Probe the Red wire at the ICM with the ignition switch in the Run position, the voltage should be the same as it is at the battery. If voltage is less then at the battery check the condition of the Red wire for looseness at terminal connections, clean any corrosion, check for any external damage, or internal wire breaks repair as needed. Next check the Ground wire resistance by probing the Black wire at the ICM and Distributor Plug. clean or repair the Black wire if a Volt / Ohm test shows more than 0.3 ohms resistance. If the trouble still continues and all other ignition system parts have checked out as good then it is time to replace the ICM. ​