Remove the injectors.
Give them a good clean externally with fuel and a lint free cloth in order to get the worst off.
Injector before.
Using Spanner and socket to unscrew injector body
Using a spanner (18 mm I think) and the same socket used to remove the injector (21 mm double depth), carefully loosen the injector body from the union housing. Unscrew them over a white sheet/piece of paper and noting the order and orientation of assembly remove the:
Shim
Spring
Top-hat
Slotted Disc
Needle
Injector Head
Complete assembly reduced to components
Again, using fuel and a lint free cloth, make sure everything is perfectly clean. I used a pin, a scalpel, a parts washer, a plastic scourer and an airline to remove any carbon from the needle tip and injector head. Be careful not to score or scuff any parts, particularly the sides of the needle as this is a moving part. Give the whole lot a wash out and blast with an air line before reassembly.
Note: Do them one at a time as you don’t want to muddle any parts. The shim is matched to the injector assembly. The injectors work on fine tolerances, so keep everything clean.
Put everything back together in the correct order and do up again with the spanner/socket combination. Don’t strip the threads! I didn’t use a torque wrench, I just tightened to about two white knuckles!
Refit, crank until engine starts and then be pleased you have saved yourself £15 per injector.
) We used to have ultrasonic cleaning kit, heavy duty chemicals & proper pressure testing cabinets, half the time you'd have to redo them if the spray pattern isn't quite right, doesn't lift at the right pressure etc. 
