When is the coil-pack going bad?

Hesitation when accelerating, and for some vehicles the check engine light or MIL lamp may blink on and off when the misfire occurs. The best way to check for this problem is to get a diagnostics check for misfires on the cylinders, once this is determined and the cylinders are isolated-it is possible to switch the coil pack to different plug wires to be sure the coil is the problem.