* Defective Upper Seal On Unit Injector
* Porosity In Cylinder Head
* Porosity In Fuel Filter Base
* Defective Seal In The Fuel Transfer Pump
1. Defective upper seal on unit injector:
Check for a defective O-ring seal on the top of the unit injector. Remove the fuel supply line at the front of the cylinder head and pressurize the cylinder head (the return to fuel tank line will have to be blocked). Look for fuel leaking from the unit injectors where they seal with the cylinder head. If fuel is leaking from an unit injector, remove the unit injector and replace the upper O-ring seal. Also depending on the amount of leakage an oil sample should be taken and checked for fuel dilution. Change oil and oil filter if necessary.
NOTE: Refer to Disassembly And Assembly, SENR6553, for the proper procedure for unit injector removal and installation.
2. Porosity in the cylinder head:
Pressurize the fuel gallery and check for porosity around the oil drain back holes. If porosity is found, replace the cylinder head.
3. Porosity in fuel filter base:
Check the fuel filter base for porosity or defects. Fuel can be transferred to the crankcase through a defective fuel filter base.
4. Defective seal in the fuel transfer pump:
Check for a defective O-ring seal between the fuel transfer pump and the hydraulic pump. Refer to Disassembly & Assembly, in this service manual.