chevy van engine losing power

Give it a tune up. For an engine to work it needs spark at the plugs and the proper air-fuel mixture. So make sure you have fuel delivery and at the proper pressure, spark at the proper timing, and air. Clean or replace filters, dirty sensors, clean throttle body, replace plugs if needed, check/replace plug wires, coil/coil packs, fuel filter, injectors... That is about all anyone can suggest given the info in your question.

everthing is ok but power is not coming

what should i do