Originally Posted by Beagle

The most common faults with the DN pintle nozzles are blocked, partially blocked or intermittently blocking jets and that should be the first thing you check when you have an injector problem. The centre hole in the SD 240/ pintle is 0,20mm dia, the average dia of a human hair is 0.10dia, a VERY small hole and all the fuel going into your engine must pass through it. The only way to check and clear these holes is with the special cleaning needles available from Bosch. Two are available:
0,18mm dia for SD 240/ (KDEP 2900/5) and 0,15mm dia for SD 240 (KDEP 2900/3).
They are expensive and you need sharp eyes, a VERY steady hand and a feather touch. We use a microscope but a 5x magnifying will suffice. Break the needle in the hole and you can throw away the nozzle! The cross hole is cleared with the same needle.

If the Jet becomes blocked the needle will over-lift giving a poor quality cone shaped spray (see sketch). A good injector will have a narrow parallel +/- 5mm dia jet that is well atomized.

Hope that helps Have a nice day.