This is not always the case-if you remove the lead to the cylinder 3 and nothing happens that means that there isn't enough spark!However,if there is a faulty spark plug this would be the problem.
By removing each lead to one cylinder at a time there should be a noticeable running difference once the lead is removed,hence no spark and poor performance from that cylinder.
If you do this on leads 1,2&4 and there is runnning fault these leads are fine!If on lead 3 there is no difference the lead is worn or the spark to that lead isn't strong enough.(more likely the lead is faulty).
Any 4 cylinder can sustain combustion on 3 cylinders but there should be a noticeable running difference.My advice is to check the leads one by one as i wrote earlier.
