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Bad coil??? I hope!!!

29K views 32 replies 10 participants last post by  kd5cqt 
#1 ·
Had a problem last week getting fire in both cylinders. I changed the plugs, and everything ran good. THIS week, I started it a couple of times, and it ran great. I went home today, and tried to fire it up, and nothing. I mean NOTHING. Can anybody tell me how to test for a bad coil? I can't really afford any expensive fixes right now, so I'd like to try and isolate the problem, and try to fix myself. Problem is that I don't have very much equipment. An ohm meter, and new plug wires, and relatively new plugs.

Any suggestions?
 
#30 · (Edited)
Quick note here. The spark plugs will not fire if you pull the plugs from the motor to test them. The ECM knows when to fire the plugs because the CKP signal senses the slowdown of the flywheels due to the cylinder compression. No plug in hole=no spark. Strange but true. The coil has positive 12 volts at one lead, switched negative at the other two leads. You test the ignition system by checking for voltage between the positive lead and both of the switched negative leads. One at a time. Also, the CKP is an AC pickup coil, or AC generator. Won't find that in any manuals. Should put out about 4 volts AC at crankover speed, if memory serves me. Which it occasionally does. There is also a way to definitely test that coil with that test light and a condenser. A coil can have the correct primary and secondary resistance when cold and short one of coils to itself when voltage is applied, causing a no fire condition. Good luck on the problem
 
#33 ·
Just got to reading through this thread and recalll a similar problem with my old FB with the evo. It started firing on one cylinder intermittently and shutting down. Turned out that the coil had a crack in one of the towers where the plug wire connected and would occasionally fire to the frame instead of through the wire. Replaced the coil and no more problems.
 
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