ENGINE DIAGNOSTIC TEST PROCEDURES
SUPPLY PUMP PRESSURE
400 Series On-Highway
(with Robert Bosch MW Pumps) (Continued)
INLET RESTRICTION TEST
Connect a tee fitting at the outlet of the primary fuel
filter and connect the line to a vacuum gauge (Figure
Run engine at full load and rated speed.
Measure and record the restriction in the 1st check
If restriction exceeds 6 in. Hg., locate the restriction
in the fuel lines to the fuel tank.
NOTE: The supply pump is very reliable and seldom
the cause of low supply pump pressure. Verify that
the specified fuel return hose with orificed fitting is
Figure 19. Fuel Inlet Restriction Test
Printed In United States of America