Ignition question
in 912 / 914 Technical Questions
11 years ago
So I'm new but well versed in mechanics...that being said here goes.
I recently noticed a formerly non-existent mild vibration while flying throughout all rpm ranges. I landed...checked carb sync, spark plugs, prop etc. (without going through all the details.) Then ah-ha found it....when doing ignition (mag) checks the "A" circuit runs rough while the "B" circuit purrs like a kitten. I isolated this (various troubleshooting) to the #3 cylinder bottom spark plug circuit. (Which is part of the "A" circuit.) Running on the #3 top spark plug only...it is smooth. It is only when you put the #3 bottom spark plug boot on that it gets a little rough. At idle it is the most observable. Merely switch which circuit you're on and it appears. So I do the usual...check the spark plug again...change it...gap it ...thermal paste etc. As well as ohm the boot and swap it with another cylinder. Same problem. So I clip the top and bottom of the spark plug cable lead from coil to boot. Same problem.
So now it's time to go deeper. So I suspect the ignition coil. Here's why. I can switch Ducati ign. Modules and make the problem appear or disappear on either one...hence not Ducati's fault! Isolated trigger coils by swapping connectors and running...and ohmed. All within specs.
So I decided to make the "B" circuit Ducati ign module, charging coil & trigger coils fire the "A" circuit dual ignition coils. The problem remained on the #3 bottom spark plug. This means that the "A" dual ignition coil that fires both the 3B & 4B (3 bottom & 4 bottom) spark plugs has successfully been deduced as the culprit.
Here's the question.....or two? #1-Am I right? (Before I spend $350+ and can't return it) #2-Can a dual ignition coil firing two spark plugs (3B & 4B) fire one well and the other not so well. It is after all a dual ignition coil. The two circuits within the coil must work independently because they do not fire simultaneously. Ok so thought of a third question ...if it is the dual ignition coil, is the circuit for the #3 cylinder bottom plug firing too weak? Can that make it a little rough? I think so. What say you?
I recently noticed a formerly non-existent mild vibration while flying throughout all rpm ranges. I landed...checked carb sync, spark plugs, prop etc. (without going through all the details.) Then ah-ha found it....when doing ignition (mag) checks the "A" circuit runs rough while the "B" circuit purrs like a kitten. I isolated this (various troubleshooting) to the #3 cylinder bottom spark plug circuit. (Which is part of the "A" circuit.) Running on the #3 top spark plug only...it is smooth. It is only when you put the #3 bottom spark plug boot on that it gets a little rough. At idle it is the most observable. Merely switch which circuit you're on and it appears. So I do the usual...check the spark plug again...change it...gap it ...thermal paste etc. As well as ohm the boot and swap it with another cylinder. Same problem. So I clip the top and bottom of the spark plug cable lead from coil to boot. Same problem.
So now it's time to go deeper. So I suspect the ignition coil. Here's why. I can switch Ducati ign. Modules and make the problem appear or disappear on either one...hence not Ducati's fault! Isolated trigger coils by swapping connectors and running...and ohmed. All within specs.
So I decided to make the "B" circuit Ducati ign module, charging coil & trigger coils fire the "A" circuit dual ignition coils. The problem remained on the #3 bottom spark plug. This means that the "A" dual ignition coil that fires both the 3B & 4B (3 bottom & 4 bottom) spark plugs has successfully been deduced as the culprit.
Here's the question.....or two? #1-Am I right? (Before I spend $350+ and can't return it) #2-Can a dual ignition coil firing two spark plugs (3B & 4B) fire one well and the other not so well. It is after all a dual ignition coil. The two circuits within the coil must work independently because they do not fire simultaneously. Ok so thought of a third question ...if it is the dual ignition coil, is the circuit for the #3 cylinder bottom plug firing too weak? Can that make it a little rough? I think so. What say you?
