Hi Changing the injectors is very easy, as Martin will testify it only takes about 10 minutes to change the whole lot, they simply pop out of the head and then they have one nut to undo. You can test the spray pattern by pulling one out, covering the whole where it came from and then try to start the engine (point the injector into a jam jar) and watch the spray. It should atomise about 2 inches from the injector nozzle i.e. turn into a mist/gas. If there is a stream pissing from the end or if they dribble they are knackered. They are pretty pricey at £31 each but they certainly made a difference to my cars performance. I did incidentally change all of the spark plugs at the same time. The injectors are of the mechanical type and so can unfortunately not be serviced though me and Martin did have a few comical attempts at cleaning them involving a lathe a peanut butter jar and a load of injector cleaner alas it did nothing. Good luck. James RG