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Spark plug coil

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brian evans

New member
I have been working on a Mercury 4 hp 4 stroke which had an oil pressure problem. This turned out to be a totally plugged intake screen.
Ok now I get the motor back together and cannot get a spark.
I have checked the wiring connectors they are all connected and I get good numbers on everything ( trigger coil 133 ohms, capacator charge coil 100 ohms,), except the ignition coil. The book says .02 to .38 on the primary I have 1.0 ohm. It says 3000 to 4400 ohms on the secondary without boots, I have 7000 ohms.
Spark plug boot checks out at 5000 Ohms , I have 12000 ohms at the plug. This thing was running before I stripped it down. I have checked out the Kill switch ( P lead) no shorts to ground. Volt meter in the plug lead shows some voltage when the engine is pulled over , but not enough to generate a spark. Is the obvious thing, the ignition coil it, or am I missing something?
Brian Evans.
 
It has an oil lamp and an oil pressure switch, but according to the circuit diagram, all the switch does is light the lamp. it is driven from the Ignition charge coil ( capacator charging coil.) The oil light goes out at 3.5 psi.
Since this is a parallel circuit, I can pull that lead and see if that makes a difference.
Brian Evans.
 
You've missed something....if it had spark before, then it should have spark now...no change with cleaning out the intake screen. If you connected everything together the way it came off...then you should have spark. You did a cleaning job and now measure all those ignition system components (for?) due to no spark is a lot of free time to spend. I admire that.
 
Ok now I got a spark, The high resistance on the coil was due to crud on the ground connections. Apparently when I put the ground leads back in I did not get them in exactly the same spot and trapped corrosion between them.
I took it all apart again, cleaned everything up and got the secondary coil resistance down to 4000 ohms and the primary coil down to .03 of an ohm , Put it back together again and got a nice fat spark on the plug.
I still do not have it running yet, but that is a fuel issue now, I did get a pop out of it so I know its alive.
Brian Evans.
 
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