I have a somewhat normal spark at the coil secondary wire, where it enters the distributor cap. I have intermittent spark at the plugs. I have changed cap, rotor, and condenser without affecting any change. When I say intermittent, I mean no spark, then for no known reason, it starts to spark again and runs fine. In both instances, I drove the truck, shut it off, went back 3 minutes later and wouldn't start again until considerable checking, cranking, cursing, crying, cursing, crying...you get the picture. When it finally decides to start and run, everything seems normal until I shut it off. 3 caps, 3 rotors, 2 condensers, no change. Help, please.
You always have a hot spark at the end of the coil wire (secondary side), even when the engine refuses to start. It just isn't making it's way through the rotor and cap and down to the plugs... right?
Just want to be sure everyone understands this. :-)
My 31 had a similar problem. Turned out that it was a wire occasionally shorting in the electrolock. Of course it never happened at home, only when I was out somewhere.
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Ole, Yes, you have it right. I always have a spark at the cap end of the coil secondary wire, even when the engine will not start. The spark appears to be adequate to run the engine. The truck sat overnight then had a new cap and rotor installed and did not start. Fire as previously described but no spark at spark plug. I pulled a different plug wire and got a single spark. AH-HAH, I said to myself. I have a bad condenser. I changed it out, with a used one from a spare engine. (I was not at home with access to my spare parts) Nothing changed. While cranking the engine and looking for a spark to the #1 plug, I decided to look for another ground and when I moved the wire to to a nearby bolt, I got a spark and the truck started, running on 5 cylinders. It started and ran normally a few more times and then failed again for several attempts (same symptoms) until it started suddenly and brought me home. My plug wires have copper wire core. I don't think they would all fail together.
Verify the distributor number and that the cap and rotor are correct . I had a similar problem after doing a tune-up on my 51 not knowing that someone had installed a 53 distributor. The rotor was shorter causing the coil to max out and overheat and fail. Fortunately I had saved the old parts and discovered the rotor was 1/8" shorter .
One thing that would change once the engine is started... and then stays the same until you shut it off.. is the primary voltage once the generator is charging.
That's probably a clue, and the reason it never stops once you have it running.
You never mentioned the points though. My dad used to always say "suspect the points first". If you haven't already, I'd polish the points with a point file first (no need to remove them or disturb the setting). I've seen that cure a slightly weak spark. I probably had primary current, but enough resistance to reduce the amperage.
Another thought... if it is a voltage thing (and the resultant primary amperage)... try jumping a fresh, or even charging, battery across to yours while trying to start. I just had some really weird things happening on a 2018 car (including an engine warning light that wouldn't go out). The battery was just beginning to fail, and apparently the voltage was dropping just a little low while starting. After starting, the battery would back up enough voltage that the alternator warning light would go out and everything seemed otherwise normal. Maybe your battery voltage is dropping more than it used to?
The battery is a couple of years old. It cranks good and spins the engine easily and fast. I gave the points a few strokes with a file and thought the spark improved a little, but the engine did not start, as a result. I have a NOS distributor which has been robbed of several parts. I will probably re-construct it and install it to see what happens. It just seems to me that if I have a spark at the coil secondary wire, there is nothing between there and the spark plug except the cap, rotor, and plug wire. I have replaced the cap and rotor. My wires work fine when the engine runs and they wouldn't all decide to act up at the same time, causing it to not start. Thanks everyone for thinking about and weighing in on my problem.
After re-reading the original post you mentioned everything runs fine until after you shut it off. You might try hot wiring to bypass the switch to see if the problem goes away.
Interesting theory Steve. Maybe the contacts in the switch has some oxidation/corrosion. When things are cold they do not have much resistance so there is enough primary voltage to the coil for the engine to start.
As the engine runs the contacts heat up due to the resistance which actually creates more resistance.
One test would be to check the primary voltage at the coil when things are cold compared to the no-start condition.
The contacts in the electrolock wear over time so it's possible that is the issue. When I reconditioned mine on the 38 I found that the rotating contacts don't always line up perfectly and do tend to wear. You can see the grooves in the stationary block and that one rotating contact had worn down. I put a buildup of solder on the rotating contact where the most wear was.
Last edited by Tiny; 01/29/2308:53 AM.
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