ENGINE DIAGNOSTIC TEST PROCEDURESSection 6•TEST INJECTION NOZZLES (Continued)Figure 25. Typical Nozzle Spray Patterns (For Orifice Type Nozzles.)SPECIFIED VALVE OPENING PRESSURECHART•400 Series On-Highway and OEM RobertBosch "MW" Pumps"MW" PumpsNew or rebuilt . . 25,337 kPa + 517 kPa(3675 psi + 75 psi)Minimum Permissible . . . . . 20,000 kPa(Used)(2,900 psi)g.CHECK FOR TIP LEAKAGE. Blow nozzle tipdry using filtered compressed air. Operate testpump to maintain pressure at about 689 kPa(100 psi) below opening pressure. Nozzle tipshould remain dry without an accumulation offluid drops at spray holes. A slight wetting afterabout 5 seconds is permissible if no dropletsare formed. Refer to Figure 26.IMPORTANTDO NOT WIPE TIP WITH FINGERS AS THISWILL TEND TO DRAW THE FLUID PRESENTIN THE SAC HOLE THROUGH THE ORIFICESAND FALSELY INDICATE A LEAK ANDREJECTION OF A GOOD VALVE.h.CHECK FUEL LEAK-OFF. Operate test pumpin quick strokes and observe for flow of fluidfrom leak-off part of nozzle. A very slight leak-off is normal. If an excessive amount of fluid isexpelled or if fluid surges from leak-off portwhen test pump is operated, nozzle is faulty.Conversely, if no fluid is present at the leak-offport the nozzle is faulty.Figure 26. Unacceptable Nozzle Tip LeakageIf nozzle passes above tests, it is suitable for furtherservice in the engine following cleaning and removal ofaccumulated carbon. Nozzles showing irregular spraypattern, leakage at nozzle tip spray holes, excessive fluidleak-off or opening pressure below minimum permissiblelimit should be replaced or serviced (disassembled,cleaned and rebuilt).CGES-240-4Printed in United States of AmericaPage 35
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