The 2002 GMC Envoy, depending on the engine, has one of two firing orders:
* 4.2L I6 engine: 1-5-3-6-2-4
* 5.3L V8 engine: 1-8-7-2-6-5-4-3
You need to know which engine is in your specific Envoy to determine the correct firing order. Check your vehicle's documentation or the engine bay for the engine size designation.