BMW E46 ignition coil and misfires
How do you identify a faulty E46 ignition coil?
Swap two coils with each other. If the fault moves to the other cylinder, the coil is faulty. Cylinders are counted from front to back. A multimeter is not enough, because the secondary winding cannot be measured, even though a burnt coil shows zero.
Do the coils and spark plugs all need replacing at once?
It is worth replacing all the spark plugs at the same time. Coils are often replaced as a set, because the failure of one can strain the others. An old or damaged spark plug can also cause the same misfire code as a coil. Also replace the spark plug boot.
What causes a misfire even though the coils and spark plugs have been replaced?
The cause can be an intake leak (a cracked hose or a bad gasket), the fuel pump or fuel pressure, the front lambda sensor or oil in the coil well. On the N42, Valvetronic can also cause the same symptom. Leave the diagnosis to a workshop if your own measurements are not enough.