May as well ask how many different engines are there? How many different uses can they be put to?
That's how you used to find which cylinder was missfiring. Remove one plug cap at a time. The one that had no effect was the faulty one. These days with electronic ignition this is not a good idea, the spark has to find a way to earth and it can destroy the electronics if it goes though them. So the test now is to dissconnect each fuel injector in turn.
-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!