Duramax Diesel Hard Start Hot - keywords crank filter fuel pressure prime pump

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Hard start hot only after the engine has reached operating temperature and then shut off.

The hard start will occur when the customer tries to restart a hot engine. The vehicle will start fine when cold. There may be no other driveability concerns noticed and no DTCs will be found. Hand priming the fuel filter manager may help the vehicle to start.

Get a large fuel sample from the fuel filter drain.

If excessive contamination is found, complete current SI repairs for Contaminants in Fuel.

Check the fuel specific gravity/API with the Kent Moore diesel fuel hydrometer. (Tool number J-38641-B)

If the vehicle has a number 1 diesel fuel, or the diesel fuel is contaminated with gasoline, the fuel API reading will be 39 to 44 or higher.

If a number 1 diesel fuel (39 API or higher) is used during high ambient temperatures it may cause a hard restart.

Get a known good sample of fuel from a nearby fuel station to verify what the normal API would be in your location.

If the fuel found in the vehicle has an API reading of 39-44, (number 1 fuel) and the fuel sample you compared to has an API reading of 30-39 (number 2 fuel) , drain the fuel system and refill with a known good number 2 diesel fuel. Evaluate the hard start hot with a known good number 2 diesel fuel.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.