Diesel Engine Hard Start When Hot - keywords 04 05 06 07 08 6.6 air API crank filter fuel heat LBZ LLY LMM operate operating P0087 pressure prime pump restart soak stall temp temperature warm

This PI was superceded to update Model Years. Please discard PIP3504A.

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

The hard start described in this PI may occur when the customer tries to restart a warm engine. The vehicle will start fine when cold. There may be no other drivability concerns noticed, and no DTCs will be found. Hand priming the fuel filter may help the vehicle to start.

Complete the current SI diagnostics for any trouble codes or symptoms found. 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 API(specific gravity) 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 may be 39 to 44 or higher.

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