Home » Duramax LLY » Duramax LLY – ENGINE DIAGNOSIS – High Fuel Consumption

Duramax LLY – ENGINE DIAGNOSIS – High Fuel Consumption


1. Prolonged high speed – high load operation.

2. Air cleaner/filter partially plugged.

3. Fuel leaks in lines, hoses at connections.

4. Restriction in exhaust system (should also be accompanied by drop in power).

5. Decrease in boost on turbocharged models, caused by vacuum leak at actuator, manifold leak, or turbo damage.

6. Brake drag

7. Converter one way clutch failure.

8. Injection pump internal problem.

9. Power loss due to worn rings, valve guides, cylinder bores, valves, etc.


1. Normal with this type of operation. Have driver reduce speed or load if possible.

2. Remove and clean air horn, intake hose, air cleaner. Replace filter.

3. Locate and repair as needed.

4. Inspect and replace bent, kinked, damaged components.
5. Correct leaks. Replace actuator or turbocharger if inoperative.

6. Repair stuck/seized calipers.

7. Replace converter.

8. Diagnose and replace as necessary.

9. Overhaul engine.


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