Re: 1982 Johnson 7.5 Spark 1 Cylinder

[Don]

Hopefully, bencraschal is correct, always check the grounds/amphenol connections first. Use a good ohm meter that reads low ohm readings clearly. You may want to eliminate the stop switch from the circuit as well, this is done by pushing the stop switch amphenol pin out of the coil 3 pin connector and retesting. You really DO need the expensive amphenol pin tools when working on these systems, please do NOT cut the leads and patch them with butt connectors. Sometimes the pins/sockets get pushed back in the rubber connectors causing a bad/no connection as well. Don’t forget to check the coil primary plug connectors (your motor may not have these), bad/corroded connections here are a big problem that is easily fixed. The spark plug leads are another problem area, the boots/spring clips get rusty/corroded and lose connections to the plug wire.
You can do a little basic troubleshooting by swapping coil connections as well. Let’s just assume that cylinder #1 has no spark and you have checked all grounds/connections/stop switch/leads. Using the amphenol tools, you could swap the coil pins around in the rubber connector. Check for spark again. Now, lets assume that now #1 cylinder fires, but #2 does not. This would indicate that both coils are good, but there is no output to cylinder #1 from the powerpack, you may have a problem with the powerpack/sensor/charge coil. On this engine, there is only one sensor, so it seems unlikely that a sensor problem would affect only one cylinder. But, you could do the same lead swap test with the sensors just to be sure.
It seems unlikely that a bad charge coil would affect just one cylinder on this engine as well. So, in my quick down/dirty test, it seems likely that the powerpack is to blame.
Let’s assume that cylinder #1 still refuses to fire after swapping the coil leads in the rubber connector. Well, this would indicate that the #1 coil/leads are bad.
Let me finish by saying that all components should be completely tested anytime there is an ignition problem and components are replaced. I realize this does not always happen, but it is the best way to be sure that marginal parts/connections don’t eventually damage new components that have been installed.