Service Manual

Lubricating Oil Contamination ISB, ISBe and QSB (Common Rail [...]
Page 7-46 Section 7 - Lubricating Oil System - Group 07
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Use the following logic to determine the source of the oil
dilution with fuel:
A worn or damaged fuel injection pump shaft seal will
allow fuel to leak into the gear housing and then into the
lubricating oil pan.
The seal is designed to provide increased sealing as the
pump case pressure increases. Pressure forces the lip (1)
tighter around the shaft.
A worn seal could leak during start-up and shutdown
when case pressure is low. A worn seal can not easily be
detected by pressurizing the pump.
The bushing (2) in the Bosch® VE fuel injection pump can
cause a seal leak. If the bushing is loose in the housing, it
will move toward the seal raising the lip (1) and providing
a leak path for fuel.