Is there timing on 1991 Chevy S-10?

Yes, the 1991 Chevy S-10 has a distributor and therefore requires timing adjustment. The specific timing will depend on the engine (2.5L 4-cylinder, 2.8L V6, or 4.3L V6) and whether it's a TBI (Throttle Body Injection) or other fuel injection system. You'll need to consult your owner's manual or a repair manual specific to your engine for the correct timing specifications.