Chapter 18 Injection Nozzles 377 Copyright Goodheart-Willcox Co., Inc. slightly open the fuel supply valve. Rapidly pump the tester hand pump for several strokes to purge any air from the injector. Open the tester pressure gauge valve approxi- mately one-eighth turn and slowly operate the hand pump to raise the fuel pressure until the needle valve lifts off its valve seat and fuel sprays from the nozzle. Allow the pressure to bleed off and observe when the needle valve reseats. Check the opening and closing pres- sures noted on the pressure gauge against service manual specifications. In general, the closing pressure should be no more that 200 psi (1375 kPa) less than the opening pres- sure. If the difference in opening and closing pressure is greater than 200 psi (1375 kPa), the valve may be sticking and will require service. Valve Seat Test Test the valve seat seal next. Dry the nozzle tip with a clean, lint-free cloth. Adjust the tester fuel pressure to 100 psi less than closing pressure. Check the nozzle tip. A slight wetting after five seconds is permissible, but a droplet of fuel must not form. If a droplet forms after five seconds, the valve seat is leaking. Back Leakage Test Checking the amount of leak-off, or back leakage, will indicate any problems with the nozzle fit in the bore or the lapped surfaces of the nozzle body and holder. Set the test pressure to within 100 psi (690 kPa) of the opening pres- sure and time the pressure drop. An average pressure drop of no more than 875 psi (6000 kPa) in six seconds indicates that the mating surfaces are not leaking excessively and that the needle valve is being properly lubricated. If the pressure drop is higher, the needle valve may fit too loosely in its bore, or the lapped surfaces may not be sealing properly. If the pressure drop is less than 300 psi (2070 kPa) over a six second period, the needle valve is not receiving proper lubrication. Lubricating passages and seams may be clogged with dirt or sulfur deposits. Spray Pattern Test To check the spray pattern of the injector, close the pressure gauge and operate the hand pump to simulate normal injector operation. On multi-hole nozzles, use long full strokes at a rate of approximately 15 strokes per minute. The spray pattern on multi-hole nozzles should be sharp with a somewhat solid pattern. The angles formed by the individual sprays should be uniform. Usually the spray of a hole type nozzle will be good if the valve seat is tight, the valve free to move, and all spray openings clear. If the spray pattern is poor, Figure 18-17A, and cannot be cor- rected by cleaning, the nozzle should be replaced. Pintle nozzles should be checked at the stroke rate of about 25 strokes per minute. If the spray is symmetrical and there are no large drops of fuel visible, the nozzle is good. If flags or streamers are visible, Figure 18-17B, the unit must be replaced. Pentaux nozzles should be checked at a stroke rate of 1–2 strokes per second. These should be short, quick strokes as opposed to the long, full strokes used with hole and standard pintle nozzles. The spray pat- tern or cone of each injector used in an engine should be similar in shape, size, and length. Chatter Test A slight chatter is normally heard as the injector nozzle opens and closes during this test. If there is no audible chatter, the injector valve may be sticking. With a Pentaux nozzle, chatter may or may not occur even though the nozzle is in good operating condition. Injectors that pass all of the above tests can be rein- stalled in the engine, unless it is time for their regularly scheduled cleaning. Before reinstalling any injector, the opening pressure must be adjusted to match service manual specifications as closely as possible. Injectors that fail any of the above tests must be disassembled, cleaned, inspected, serviced with replacement parts as needed, reassembled, and adjusted. The following section outlines a typical disas- sembly, inspection, and reassembly procedure. Disassembly Complete disassembly of the nozzle holder and nozzle is recommended for inspection of all components. Many nozzle holders require the use of special fixtures and fixture holding plates for safe disassembly. Use the manufacturer’s recommended fixtures and tools to prevent damage to components such as the nozzle locating pins. The following sections outline procedures performed by fuel injection service shops: 1. Wash all external dirt, grease, and carbon deposits from the holder assembly with a suitable cleaning agent. 2. Remove the nozzle gasket from the nozzle. 3. Use a brass wire hand brush to remove hardened deposits of dirt or carbon. Do not allow the wire brush to come into contact with the nozzle spray holes. A B Figure 18-17. Operate the tester and check the spray pattern. A—Bad hole-nozzle spray pattern. B—Bad pintle-nozzle spray pattern.