Category Archives: Diesel Engines

Testing of Fuel Injector

Testing of fuel injector is carried out as follows. Mount the fuel injector in its test rig and connect up the oil supply. Under no circumstances should hands be placed under the injector spray. The high velocity oil jet can penetrate the skin and cause blood poisoning. With the injector priming valve open, operate the hand pump to prime the injector. Once the fuel flows from the priming valve it can be closed.



  1. Oil Container
  2. Pressure Gauge
  3. Shut off valve
  4. Pump lever
  5. Test pump
  6. Injector
  7. High Pressure fuel pump

Operate the pump rapidly for several strokes. The injector should open with a high pitched chatter and fuel should be emitted in a fine cloud. After the injector opens, check to make sure the pressure does not fall off too quickly.

To test for the tightness between the nozzle needle and seat, operate the hand pump slowly to gradually increase the pressure until it is just below opening pressure. Maintain the pressure for a few seconds and ensure injector is not dripping.

To test for tightness between needle and guide, operate the hand pump to increase pressure until it is just below opening pressure. See how long it takes the pressure to fall off. If the pressure falls quickly the needle and guide should be replaced.

Where nozzles are cooled internally, these spaces should be pressure tested to check for tightness. Blank off one of the fuel valve cooling connections and fill the injector cooling space with water or fuel, depending upon the cooling medium. Then connect a low pressure air supply to the other connection. Leave the air on for a short period of time and test for internal or external leakage. Testing of fuel injector is usually carried out at an interval of 2000 running hours for marine diesel engines.

Following points to be remembered while testing of fuel injector:

  1. Visually examine the injector just after taken from cylinder head. Pressure test and find opening pressure in service.
  2. Check injector setting pressure, formation of trumpets and carbon accumulation, corrosion at the nozzle, etc.
  3. Spray pattern assessment and prompt re-seating.
  4. Drip proof. No droplet formation at set pressure minus 10 bar, held steady and also upon closing.
  5. Injector lift diagram may be taken.
  6. Recommended assembly procedure to be followed (Like tightening torque, etc.) and handle parts carefully.