12 Fuel Injection Nozzle Maintenance Procedure

Fuel Injection Nozzle Maintenance is a very important factor to make the vehicle engine burn the fuel better in every situation. If the nozzle is clean then it can operate very effectively to spray the fuel. In this article, I will discuss the 12 fuel injection nozzle maintenance procedure.


Fuel Injection Nozzle Maintenance

The performance of a modem high-speed oil engine depends largely upon the proper functioning of its fuel injection system. For maximum efficiency in operation, the engine must be not only provided with fuel in quantities exactly timed and proportional to the amount of work it is required to do but al o that it should receive each charge of fuel in a condition such that it can be completely consumed, without causing smoke in the exhaust.

This briefly, is the function of the nozzle, which is held in position in the cylinder head by the nozzle holder. As the nozzle may have to deal with many hundreds of fuel charges per minute, with widely varying conditions of pressure and temperature, the unerring precision necessary in the production of these parts will be appreciated.

All nozzles, irrespective of type, should be moved from the engine for examination at regular intervals. Just how long this interval should be, however, is difficult to generalize, because of the widely different conditions under which the engine operates. On certain installations, such as generating plant or pumping station sets, where operating conditions of the engine are good and the tank fuel and filtering systems are maintained in first-class order it is often sufficient that nozzles are tested as that infrequently yearly.

12 Fuel Injection Nozzle Maintenance Procedure


The most suitable bench for nozzle maintenance is the zinc, linoleum of plastic covered free from dust, dirt fillings, grease, or acids where no other work is done and where the use of cotton waste and fluffy rags is useless. It should also be provided with a small space.

So the procedure is-

1. Check the complete injector on the nozzle setting outfit for the nozzle pressure setting and seating.

2. If the nozzle is faulty, clean it.

3. Examine the nozzle for carbon and whether the vale lifts out freely. Brush all carbon from the outside with a brass wire brush. Place body and valve in clean petrol, fuel, or an approved alternative to soften carbon.

Note- The nozzle should be free from all damage, and it mustn’t be “blued” due to overheating All polished surfaces should be relatively bright without scratches or dull patches. It is essential that the pressure surfaces.

4. Clean out small feed channels bores “G” dift or wire of 1.70 mm diameter. These bores are rarely choke inserted of drill or wire by hand will be sufficient.

5. Insert a special groove scraper until the nose is located in fuel gallery “H”. Press hard against the side of the cavity and rotate to clear all carbon deposits from this area.

6. Insert the appropriate dome cavity scraper according to nozzle type and in the same manner as operation 5, remove any carbon deposit adhering inside of the dome.

7. With the appropriate seat scrapper according to nozzle type, clean all carbon from valve seating “J” by rotating and pressing the tool onto the seating.


(a) Hole-type nozzles- Clear spray holes by using of probing tool fitted with appropriate size cleaning wire. All kits are supplied with the most popular sizes of cleaning wire, but if the correct size is not known, it can be ascertained by a careful trial of wires in holes.

Extreme care must be taken, however, to obviate the danger of wires breaking in holes, as such particles are almost impossible to remove. The cleaning wire should be fitted in the tool chucks so that it produces for only about 1.5-2 mm thus giving maximum resistance to bending.

Enter wire into hole pushing and rotating gently until hole is cleared. The auxiliary hole of a pintaux nozzle may be cleaned in the same manner.

(b) Pintle-type nozzles- For cleaning the orifice of a (DN) pintle-type nozzle, select the appropriate size probe from the cleaning head and insert this in the nozzle body pintle hole. Pass the probe down the bore orifice nozzle until it protrudes through the. orifice then turn with a rotary motion until all carbon is cleared.

To clean the pintle end of a pintle valve, use the wire brush, dislodging any hard pieces of carbon with a piece of wood or brass strip. Care must be exercised with the nozzle valve, and in particular the pintle, to prevent damage to either, as a scratch or burr may cause valve leakage or spray distortion.

9. Assemble the nozzle into a suitable flushing tool, with the nozzle end towards the smaller thread connector which should be coupled to the nozzle setting outfit. The flushing tool should be arranged with the open end pointing downwards to facilitate particles being washed out.

10. Clean the needle valve tip carefully by brushing away carbon with a brass wire brush. To assemble the valve into the nozzle, immerse both items in clean fuel oil, or an approved alternative and fit them together under the surface, to prevent the closely fitting lapped surfaces from being touched by hand.

Note- If the nozzle is blued or the seating has a dull circumferential ring indicating wear or pitting, the complete unit should be set aside for special attention by a servicing center. In no circumstances must an attempt be made to lap the nozzle valve and body unless specialized knowledge and equipment are available.

11. Ensure that the lapped pressure faces “B” on the nozzle and “D” on the holder are clean and free from dirt or metallic particles. If the holder has been dismantled, all parts should be thoroughly washed in petrol, fuel, or an approved alternative before re-assembly, and particular care should be given to the pressure face.

12. Place the nozzle on the pressure face of its holder and secure it in position by the cap nut. It is important to remove the tension of the nozzle holder spring during this process, particularly where the holder carries locating dowels, as otherwise false locations may be obtained and damage sustained by the pressure faces.

Finally, tighten the cap nut with a spanner taking care not to over­ tighten, as this may cause distortion and lead to seizure of the nozzle valve. Fit the assembled unit to the nozzle setting valve and adjust the pressure to the engine maker’s recommended setting. If the nozzle is to be stored, smear lightly with a baseline before packing away.

Adjusting and Testing of Nozzle

Remove the injector from the cylinder head and clean the carbon deposits, if any, by washing them thoroughly in petrol. Remove the nozzle and dip it in the clean fuel and the nozzle needle too. After cleaning the needle, insert it into the nozzle body. Nozzle needle and body are lapped together and must not be exchanged.

So the tests are-

Initial Test

Initial tests are of two types. Visual tests and Slide tests.

Visual Test-  After cleaning, the used nozzle should be visually inspected. Look on the nozzle needle for damaged or rough needle seat, for worn or damaged or carboned seat, and for round needle holes.

Slide Test- After the visual test all nozzles should be given a slide test. First, dip the nozzle needle in clean fuel and insert it into the nozzle body. Holding the body almost vertically, pull up the needle by one-third of its engaged length. When released, the needle should slide down by its height.

Testing with Nozzle Tester

The following is tested on the nozzle tester :

  • Opening pressure
  • Leakage
  • Chattering characteristics and spray pattern.

Use clean test oil for testing. The oil must be cleaner The nozzles are adjusted by their respective nozzle holders.

When clamping the nozzle into the nozzle holder, ensure the sealing surface is clean and unplugged. Place nozzle on sealing surface of nozzle holder, tighten cap nut first by hand and then with a well-fitting wrench to torque 6 -8 kg-m.

Connect the nozzle holder with its respective delivery pipe to the outfit. To test for nozzle jamming, press the hand lever of the nozzle tester down vigorously a few times (approximately 6 -8 downward movements per second) with a pressure gauge bypass. With the nozzle moving properly, the nozzle should chatter with a shrill whistling buzz.

Opening Pressure

The opening pressure is specified under the description and operation for individual engines and should be adjusted correspondingly. With the pressure gauge open to pressure slowly depress the hand lever until the nozzle ejects with slight chattering. Take a reading on the pressure gauge, if this pressure differs from the specified opening pressure, it is necessary to change the total shim thickness.

Caution. When the pressure gauge is open to pressure, increase and decrease pressure slowly otherwise the gauge may be damaged.

Leakage Test

Operate the hand lever of the nozzle tester until the pointer on the pressure gauge indicates 20 kg/cm2 (285 p.s.i.) below the specified opening pressure. The nozzle is considered leak-proof if no drop of fuel emerges at the end of the nozzle within 10 seconds.

Chatter and Spray Pattern Test

For these tests, the pressure gauge must be by­ passed. Testing speed range: 1 stroke in approx. 0.2 to 2 sec (5 to 112 downward movements per sec).

Chatter test- These types of nozzles chatter in the entire range of attainable lever velocity (lowest test velocity: One downward movement per second). Single non-chattering in the intermediate range is of no significance.

Spray pattern- At low test velocity, atomization is course. In the non-chattering ranges, non-atomized streams are formed.

Nozzle Setting Outfit-Hand Lever Type



The nozzle setting outfit (Fig. P16-14) is a necessity when it is desired to adjust the opening pressures of nozzles and to inspect their spray qualities. The model described is suitable for “S” type nozzles and holders that is, for those normally fitted to commercial vehicles, tractors, and smaller marine engines, but an adaptor is available for use when it is desired to test the “T”, or any other types as fitted to larger stationary and marine installations.

Note- The injection pump incorporated in the outfit has been specially designed for its particular function, and is not intended to be used for other purposes.

When assembling the handle to the nozzle setting outfit, the adjusting screw on the base casting which limits the downward travel of the handle should be screwed in until the screw is secured by tightening the horizontal locking screw.

The fuel tank has a capacity of approximately 1 liter and contains a paper filter element to ensure the cleanliness of fuel delivered through the pumping element to the nozzle under test. Never connect the unfiltered fuel supply directly to the pump inlet. This will cause dirt and foreign matter to be pumped through the nozzle under test, entirely negative any cleansing which has been carried out and damage the valve faces.


The fuel injector nozzle is a small device but has a big impact on the Internal combustion engine combustion process. All the nozzle ports must be correct and perfect to throw the fuel into the hot air. Also, the nozzle hole is important to atomize the fuel properly.

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