Duramax engines are eight-cylinder, 6.6-liter engines manufactured by General Motors. The LLY version was in production from 2004 to 2005, and is a common engine for full-size Chevrolet pickups. The fuel system for the Duramax LLY engine is highly-pressurized, and requires a regulator to maintain the correct pressure. The replacement procedure for the fuel pressure regulator is the same for all vehicles with a Duramax LLY engine.
Disconnect the air intake pipe and alternator with a socket wrench. Detach the electrical connectors for the air conditioning clutch and air conditioning cut-out switch. Remove the mounting bolts for the air conditioning compressor, and push the compressor to the right of the engine.
Lift up the latches on the connectors for the main wiring harness on the engine, and release the clip on the harness to detach the connectors. Disconnect the connector from the barometric pressure sensor. Remove the mounting bolts on the bracket for the engine wiring harness with a socket wrench, and disconnect the bracket.
Disconnect the electrical connectors from the engine coolant temperature sensor, fuel temperature sensor, oil level sensor and fuel pressure regulator. Detach the water outlet tube from the engine. Release the clamps for the distribution block hoses, and disconnect the hoses. Disconnect the retaining bolts for the Exhaust Gas Recirculation (EGR) hose, and release the clamp on the hose so you can push it aside.
Clean the fuel pressure regulator and injection pump with solvent 12377981 and compressed air. Disconnect the screws on the fuel pressure regulator with a T25 TORX tool, and detach the fuel pressure regulator.
Coat the new O-rings for the fuel pressure regulator with clean engine oil, and mount them to the new fuel pressure regulator. Install the new fuel pressure regulator, and tighten its screws to 35 inch-pounds, with a T25 TORX tool. Tighten the screws for the fuel pressure regulator again to 62 inch-pounds.
Install the remaining components by performing steps 1 through 3 in reverse order. Tighten the mounting bolts for the EGR hose and the main engine wiring harness to 15 foot-pounds with a torque wrench. Tighten the bolts for the air conditioning compressor to 37 foot-pounds.
Crank the engine until it starts to prime the fuel system. Allow the engine to idle and check for fuel leaks.
