Duramax LB7 Fuel Injector Sleeve

2001-2004 Duramax LB7 Fuel Injector Sleeve. 

The injector sleeve acts as a barrier between the fuel injector and the cylinder head, preventing the escape of combustion gases and coolant. If the seal is bad, it can lead to engine misfire and damage to the injectors. To maintain the proper functioning of the injectors and prevent these issues, it is recommended to replace the injector sleeve whenever the injectors are being serviced or replaced.

What is the Difference Between an Injector Cup and Injector Sleeve?

The short answer is... nothing. They're one and the same.