How do you set timing on a 4.3 Chevy s10 pickup?

It all depends on what year the truck is. If it is the older version with the round distributer cap, you need a timing light. Connect the timing light to the number 1 cylinder, which is the front one on the drivers side. next you have to put the computer in base timing mode. To do this you need to locate the timing connector, which is usually located

in the passenger side under the carpet ,below the hvac unit. Unplug the connector and start the engine, then shine the timing light on the timing marks and loosen the distributor and turn it unill the marks line up .Then tighten the distributor, and reconnect the connector. If it has the flat cap , the timing is set with a scanner .