ENGINE DIAGNOSTIC TEST PROCEDURES
TEST INJECTION NOZZLES (Continued)
Figure 25. Typical Nozzle Spray Patterns (For Orifice Type Nozzles.)
SPECIFIED VALVE OPENING PRESSURE
400 Series On-Highway and OEM Robert
Bosch "MW" Pumps
New or rebuilt . . 25,337 kPa + 517 kPa
(3675 psi + 75 psi)
Minimum Permissible . . . . . 20,000 kPa
CHECK FOR TIP LEAKAGE. Blow nozzle tip
dry using filtered compressed air. Operate test
pump to maintain pressure at about 689 kPa
(100 psi) below opening pressure. Nozzle tip
should remain dry without an accumulation of
fluid drops at spray holes. A slight wetting after
about 5 seconds is permissible if no droplets
are formed. Refer to Figure 26.
DO NOT WIPE TIP WITH FINGERS AS THIS
WILL TEND TO DRAW THE FLUID PRESENT
IN THE SAC HOLE THROUGH THE ORIFICES
AND FALSELY INDICATE A LEAK AND
REJECTION OF A GOOD VALVE.
CHECK FUEL LEAK-OFF. Operate test pump
in quick strokes and observe for flow of fluid
from leak-off part of nozzle. A very slight leak-
off is normal. If an excessive amount of fluid is
expelled or if fluid surges from leak-off port
when test pump is operated, nozzle is faulty.
Conversely, if no fluid is present at the leak-off
port the nozzle is faulty.
Figure 26. Unacceptable Nozzle Tip Leakage
If nozzle passes above tests, it is suitable for further
service in the engine following cleaning and removal of
accumulated carbon. Nozzles showing irregular spray
pattern, leakage at nozzle tip spray holes, excessive fluid
leak-off or opening pressure below minimum permissible
limit should be replaced or serviced (disassembled,
cleaned and rebuilt).
Printed in United States of America