The 1983 Chevy Pickup straight-6 (likely a 250 cubic inch or a 4.1L, or possibly a 292 cubic inch or 4.8L) uses a
1-5-3-6-2-4 firing order. This is standard for most inline-six engines of that era.
However, verifying this with your specific engine's casting number or a workshop manual is always recommended. The firing order might be stamped on the engine block itself, near the distributor.
