What is the difference between odd firing order and even firing order?

Answer 1

Many V6 engines have been based on V8 designs. One characteristic of these engines is a notorious odd-firing behavior.

Purpose-built V6 engines use one crankpin per cylinder for a smooth ignition 120 degree ignition pattern. Most V8 engines share a common crankpin between opposite cylinders in each bank. That is, the crankshaft has just four pins for eight cylinders, and a cylinder fires every 90 degree for smooth operation.

When two cylinders are "removed" for a V6 variant, the firing order becomes uneven. One 90 degree ignition is removed, so the engine fires at 90 degree, 90 degree, 90 degree, and skips one 90 degree. This leads to a rough idle and increased stress on the engine mounts and chassis.