ISC, ISCe, QSC8.3, ISL, ISLe3, ISLe4 and QSL9 Engines – Air Compressor Air Pressure Rises Slowly

Air intake system restriction to air compressor is excessive

Replace the air compressor air cleaner (if installed). Check the air intake piping. Check engine air intake restriction if the air compressor inlet is plumbed to the vehicle or equipment intake system. Refer to
Procedure 010-031 (Air Intake Restriction) in Section 10.

Air system leaks

Block the vehicle wheels and check the air system for leaks with spring brakes applied and released. Check for leaks from the air compressor gaskets and the air system hoses, fittings, tanks, and valves. Refer to the OEM service manual. For applications fitted with selective catalytic reduction exhaust systems, check the air supply line to the dosing control unit.

Air governor is malfunctioning or not set correctly

Check the air governor for correct operation. Refer to
Procedure 012-016 (Air Governor) in Section 12 and the OEM service manual.

Carbon buildup is excessive in the air discharge line, check valve, or cylinder head

Check for carbon buildup. Replace the air compressor discharge line, if necessary. Refer to
Procedure 012-003 (Air Compressor Carbon Buildup) in Section 12 and
Procedure 012-007 (Air Compressor Cylinder Head, Single Cylinder) in Section 12.

Air system component is malfunctioning

Check the operation of check valves, alcohol evaporators, air dryers, and other OEM-installed air system components. Refer to the manufacturer’s instructions.

Unloader valve is malfunctioning

Check the unloader valve and unloader body seal. Refer to
Procedure 012-014 (Air Compressor) in Section 12 and the OEM service manual.

Air compressor intake or exhaust valve leaks air

Inspect the air compressor intake and exhaust valve assemblies. Refer to
Procedure 012-007 (Air Compressor Cylinder Head, Single Cylinder) in Section 12. If the air compressor head is
not serviceable, replace the air compressor head.
Refer to Procedure 012-014 (Air Compressor) in Section 12.