What is the firing order for a 4 cylinder engine?

Learn the most common firing order for a 4-cylinder engine

A firing order is the sequence in which the spark plugs fire in an internal combustion engine. It is determined by the engine manufacturer and is designed to optimize engine performance, balance, and efficiency. The most common firing order for a 4-cylinder in-line engine is f 1-3-4-2.

However, some “boxer” (opposed) and British engines have a different firing order. The Subaru EJ20 2.0L, for example, has a firing order of 1-3-2-4, while the Subaru EJ22 2.2L has a different firing order of 1-2 3-4.

Why you may need to know the firing order or the engine layout

Knowing the firing order is most important on older engines that have a distributor or distributorless (DIS) ignition system, or any engine that uses spark plug wires. If you’re replacing spark plugs and don’t pay attention to which wires go to which plugs, you’ll need the firing order to get them back into the right place.

Here’s how that works:

Here’s the engine layout diagram for a Ford 302 engine.

The cylinder layout of the Ford 302 engine

If you mix up the spark plug wires all you have to do is locate the distributor tower for cylinder number one. In this example the distributor rotates in a counterclockwise fashion, so we can figure out the firing order is following the distributor layout. In this case, the firing order is 1-5-4-2-6-3-7-8. Based on that order we can tell that this 302 engine is not Ford’s 302 “Boss” high output engine because the firing order for that engine is 1-3-7-2-6-5-4-8.

The firing order can help you diagnose a misfire problem

Here’s an example of how to use the firing order to diagnose a misfire code on the Subaru Boxer engine.

This Subaru 4-cylinder engine has distributorless ignition. This is also known as a waist spark ignition system when a coil fires from the center electrode to the side electrode on the power cylinder and from the side electrode to the center electrode on the partner cylinder that’s on its exhaust stroke. If I were to see a trouble code P0301 along with a P0302, I would immediately suspect a bad ignition coil rather than a spark plug issue. That’s because both plugs share a single coil within the DIS coil pack.

Subaru engine layout

In summary, If you know the firing order you can replace spark plug wires in the proper order, locate the problem cylinder by it’s trouble code, and help diagnose a bad DIS coil pack.

©, 2024 Rick Muscoplat