TAKEN FROM AUTO WORKSHOP MANUAL
venum wrote:^^^ neither do I
Mitsu do one of your great posts on COPs nah dude
Though coils are very reliable, they sometimes fail. Coils run hot because of the voltage that is constantly surging through them. Over time, the combination of heat and voltage may break down the insulation between the windings, coil housing or tower. If a coil problem is suspected, the coilâ€™s primary and secondary resistance can be measured with an ohmmeter. If either is out of specifications, the coil needs to be replaced.
A short or lower-than-normal resistance in the primary windings allows excessive current to flow through the coil, which can quickly damage the ignition module. This also may reduce the coilâ€™s voltage output resulting in a weak spark, hard starting and hesitation or misfire under load or when accelerating.
An open or high resistance in the coil primary windings will not usually damage the ignition module or PCM driver circuit right away, but it may cause the module to run hot and shorten its life. With this condition, coil output will be low or non-existent (weak spark or no spark).
A short or low resistance in the coilâ€™s secondary windings will result in a weak spark, but will not damage the module or PCM driver circuit. An open or high resistance in the coilâ€™s secondary windings will also cause a weak spark or no spark, and it may also damage the ignition module due to feedback induction through the primary circuit.
An important point to keep in mind with respect to all types of ignition coils is that when the magnetic field collapses, the high-voltage surge has to go someplace. If it canâ€™t go to the spark plug, it will find another path to ground - which may be back through the ignition module, PCM driver circuit or through the insulation inside the coil itself. This can be very damaging to these parts. So never disconnect a plug wire or COP coil while the engine is running. It can be very damaging as well as dangerous to you should you become the path to ground.
When a coil failure occurs on a distributor ignition system, it affects all of the cylinders. The engine may not start, or it may misfire badly when under load. But with multi-coil ignition systems, a single coil failure will only affect one cylinder (or paired cylinders in the case of waste spark DIS systems).
NOTE: YOUR SPARK PLUG IS PART OR THE COIL SECONDARY CIRCUIT
HAVING READ THE ABOVE IT WOULD BE A GOOD PRACTICE TO HAVE A SPARE PLUG TO PLUGIN THE COIL PACK AND GROUND IT TO THE ENGINE LEAVING THE ORIGINAL ONE ON THE CYLINDER. THIS IS IF YOU WANT TO CHECK YOUR CYLINDERS FOR MISFIRE OR FOULING.BY DOING THIS YOU WOULD NOT HAVE AN OPEN CIRCUIT ON THE COIL SECONDARY.THIS IS MY METHOD OF CHECKING WITHOUT CREATING DAMAGE.