Weak spark and hesitation

[CP951]

Hello,
I'm new here and hope to get some advise. My car has developed alot of hesitation & black smoke whenever on a highish level of boost (around >7psi). It runs well otherwise. Fuel delivery and pressure are fine. There's no boost leakage. All fuel injection components checked out ok. The only fault is a weak spark noted with cylinder 5. The other sparks seems OK. I've check the plug holder resistance, which is ok. The power input to all ignition coils and ignition amplifier seems fine. I then switched the 3 pin plugs to the 2 ignition amplifiers around and spark now seems like normal with cylinder number 5. However there is now NO spark with cylinder number 3. The pin number corresponds at the same position for cylinders 3 and 5 of the 2 plugs. I understand what might have happened is the weak spark of cylinder 5 gets blown out whenever on highish boost, hence no combustion and the rich exhaust. My question is this, I know I have to replace the ignition amplifier on the left, but how about the ignition coil for cylinder three. I'm thinking this because with the same pin output I got at least some spark though weak with cylinder 5 coil but nothing when plugged into cylinder 3 coil. Does that mean my cylinder 3 coil is weaker and failing? Are there any other tests I could do? Any advise appreciated. Thanks.

[audiman]

Right then, if the amp was the problem you would have no spark what so ever. If the spark is being blown out, then suspect the coil to be dying. The 2 amps both have 3 channels, but on one only 2 are used. You can rewire the plug so that the unused channel is now in action, If it is that. Coils are quite a common failure on the cars now, as they are all getting old.

[CP951]

OK thanks. But then if the cylinder 5 coil is defective, surely the spark would have remained weak after I swapped the plugs around. My problem lies with cylinder 3 coil, which went from having a good spark to NO spark after swapping the plugs around. I know the amp is failing and its signal is weak. Is it correct to say that just because the cylinder 3 coil did not spark with a weak amp signal, it is then assumed failing? (Knowing cylinder 5 coil did at least produce a weak spark with the same weak signal)