Most of the time the coils either work or they don't. Much like a fuel pump.
I'd be willing to bet that the issue is in one of your plug wires. Check the resistance of each plug wire. If it'* out of the specs (as detailed in a Chilton'*) then replace the faulty wire. Or, to make things simple, replace them all.
Are you getting a check engine light? If so, scan the codes.