Description: All models. 8.1l. Express, savana. 8.1l. 8.1L, 8 cyl gas. This part requires programming and/or special setup procedures GM Service Information describes the procedures and special tools needed to ensure proper operation in the vehicle Helps keep engine timing and fuel injection running in sync Helps provide proper alignment, positioning, and spacing for easy installation Synchronizes engine valves and pistons for excellent engine performance