There are three different types of injectors and one of these is not serviceable. If you find yourself in possession of the type that cannot be reconditioned, please try to obtain one which can be for exchange purposes. The two serviceable types are identifiable by a wire ‘c’ clip fitted to the nozzle end of the injector. The non-serviceable type has the nozzle end held into the body by crimping. All injectors, after installation need to be bled to expel any air from them. This will ensure that they work satisfactorily. If any of the fuel lines to the injectors is disconnected, they too will need bleeding to purge them of air.
If your engine starts on less than 6 cylinders, the fault may be trace to wither numbers 2 or 5 fuel injector. Often the misfiring of one of these two cylinders is caused by a faulty banjo bolt part number 518630, not a failed injector. Substitution of another injector that is known to be working will pin point these banjo bolts that include a non return valve, to be a fault.