The firing order of a Chevy V-6 engine varies. On rear-wheel-drive cars and trucks, one version of the engine has the firing order 1-5-3-6-2-4, while the alternate version has the firing order 1-2-3-4-5-6. On front-wheel-drive cars and minivans, the firing order is either 1-6-5-4-3-2 or 1-2-3-4-5-6.
An engine's firing order refers to the sequence in which its spark plugs fire. The sequence is established by the way the spark plug wires are routed from the distributor cap to the spark plugs in each engine cylinder. If the spark plugs are set properly, the rotor inside the distributor cap aligns with the number 1 spark plug terminal when the piston is at top dead center on the compression stroke of the cylinder.