LB7 Injector Cups
Out of the four Duramax motor types: LB7, LLY, LBZ, LMM (and LML now) the LB7 was the only model that came equipped with injector nozzle sleeves c
ommonly referred to as injector cups. The injector cups are seated tightly into the cylinder head and held in by the injector via the injector hold down. The problem that is associated with these sleeves is when they lift up out of the head slightly and begin to leak compression, causing pressurization of the cooling system. This is commonly mistaken for blown head gaskets, and end up in costly and unnecessary repairs.
The largest symptom of a pushed injector cup is coolant system pressurization, usually resulting in "coolant puking" from the coolant reservoir after hard
acceleration runs. This is usually and early symptom and is the first thing that will get your attention. If not taken care of, the leak can progress until the coolant will puke from the reservoir even at idle and can even allow coolant to start entering the cylinders after the motor has been shut down, causing much more potential damage to a motor through hydro locking, cylinder wall rust and pitting. But if you notice coolant in your oil or excessive crank case pressure, chances are you have a blown head gasket and will require removal of the heads and replacement of the gaskets.
Injector cups can be repaired in most cases by resealing the injector nozzle with red hi-temp 271 loctite. In some cases the injector cup will have excessive heat damage and will need to be replaced and resealed with red loctite.