Alex, you should be able to do a continuity check on the secondary wiring inside the coils. Take a VOM and ohm out the two spark plug wire terminals on each coil. I think these coils (being the secondary) should read continuity between the terminals. I had a 6 cyl GM 3.8L that used the waste gate method of burning excess fuel on the exhaust stroke so each cylinder fired twice on each crank rotation (once to ignite and once during exhaust). Anyway, the coils are just a step-up transformer and you should be able to check the high voltage side in each coil. Note this is done with the car OFF, and the coil wires removed from that coil your testing. As you do each ciol, replace the wires then go to the next one. All the coils should read close to each other. If you get one (or more) with no reading, that secondary is 'open'. Your only testing one coil at a time and only those two spark plug wire outputs. That 3.8L I had had two oif three coils open. It ran great but when a heavy load (hard accell and A/C) it would cut out like someone was turning off the iggy.