I have a 03 2500 duramax with 250,000+ miles. When at idle, the exhaust is thick with blue smoke and smells like unburned diesel. Fuel mileage is still great, I can see no loss of power, and can not see any water in the oil, I took the truck to the dealer asking for the air flow censor to be replaced. Dealer said motor is almost gone and needs replacing. Any advice?
I doubt the engine is almost gone. Did they perform a compression test? I would almost bet that the injectors are faulty. I would suggest taking the vehicle to a different dealer if possible and have them check the cylinder balance rates and perform a fuel pressure regulator test and max fuel pressure test.