COVER AS-SOUND SUPPRESSION 3727674 - Caterpillar

Probable Causes
Faulty upper seal on unit injector
Porosity in the cylinder head
Porosity in fuel filter base
Faulty seal in the fuel transfer pump
Excessive internal clearances in the fuel transfer pump
Faulty unit injectorRecommended Repairs
Faulty Upper Seal on the Unit Injector
Check for a faulty O-ring seal on the top of the unit injector. Remove the fuel supply line at the front of the cylinder head. Plug the return line to the fuel tank. Pressurize the cylinder head. Look for fuel that is leaking between the unit injectors and the cylinder head. If fuel is leaking from an unit injector, remove the unit injector and replace the upper O-ring seal. If necessary, change the oil and the engine oil filter.Note: For the proper procedure for the removal and for the installation of unit injectors, refer to Disassembly And Assembly.Porosity in the Cylinder Head
Pressurize the fuel gallery and check for porosity around the oil drain holes. If porosity is found, replace the cylinder head.Porosity in the Fuel Filter Base
Check the fuel filter base for porosity or defects. Fuel can be transferred to the crankcase through a faulty fuel filter base.Faulty Seal in the Fuel Transfer Pump
Check for a faulty O-ring seal at the bottom of the sleeve in the fuel transfer pump. Refer to the Disassembly And Assembly Manual.Excessive Internal Clearances in the Fuel Transfer Pump
Check for excessive clearance between the tappet and the sleeve in the fuel transfer pump. Refer to Troubleshooting, "Fuel Transfer Pump".Faulty Unit Injector
Faulty unit injectors will normally cause the engine to misfire which will cause the engine to run rough. Faulty unit injectors may also provide a path for fuel leakage into the engine oil. Remove the unit injectors. Use the 1U-6661 Pop Tester Group to check the injectors for proper operation. Refer to Special Instruction, SEHS8867 for additional information. Refer to Tool Operating Manual, NEHS0738, "Using the Injector Seating Tool " and Tool Operating Manual, NEHS0610, "Using the 128-8822 Tool Group on 3114, 3116, and 3126 Engines with Mechanical Unit Injectors (MUI)" whenever an injector needs to be replaced. Also, refer to Video Tape, LEVN4032, "Troubleshooting Guide for the 3100 Family of Diesel Engines" and Video Tape, LEVN4732, "Injector Seating Procedure".