One grotty injector, covered in grit, oil and tired old seals
Place into an ultrasonic cleaner with some decent parts cleaner fluid.
Press start and the dirt begins to fall off.
A few mins later and you have a nice clean injector.
Check inside to see how clean the outlet hole is.
Fit new gaskets and seals.
Job done, 4 ultrasonically cleaned injectors ready to be fitted.