Fuel Injection System - 6.9L Diesel: Testing: Injectors

1. Remove injection nozzles from engine. Test injectors using calibration fluid at room temperature. Bleed air out of tester by opening tester valve slightly and pumping handle several times. Close valve.
2. Install injection nozzle on tester. Open tester valve and pump tester handle quickly 8-10 times to bleed air from nozzle. Slowly lower tester handle and note pressure shown on gauge as injector nozzle opens. Repeat several times to obtain accurate reading.
3. Normal injection starting pressure should be 1800-1950 psi (126-137 kg/cm² ). If injection starting pressure is below 1425 psi (100 kg/cm² ), replace injector.
4. Using injector tester, maintain pressure at about 200 psi (14 kg/cm² ) below nozzle opening pressure. No fuel leakage should occur. Slight wetting of tip after 5 seconds is OK. DO NOT  wipe tip of nozzle with fingers. If leakage does occur, injector must be replaced.
5. Operate tester using quick strokes while observing flow from injector return ports. A slight leak-off of 1 or 2 drops per stroke is normal. If a solid stream is expelled from return port, injector must be replaced.
6. Build up pressure in the injector tester to just below injection starting pressure. Quickly lower handle on tester and observe fuel spray pattern. Fuel should be uniformly atomized. Droplets or a solid stream of fuel indicates a faulty nozzle. See Fig 1 .

Fig 1: Injector Spray Patterns Injector must not drip when needle valve is closed.