Why Are Misfires So Hard To Diagnose?

Even if you're not a car enthusiast, you can probably recognize a misfire when one happens to you. These annoying problems tend to feel like stuttering or hesitation, either at idle or while accelerating. Depending on the severity of the problem, you might feel your engine stumbling or vibrating or even notice that the car wants to stall.

In technical terms, a misfire occurs when one or more engine cylinders fail to produce complete production. These events can cause your car to lose power and fuel efficiency, and they may even result in internal damage. Repairing misfires is critical to keeping your car on the road, but why do they happen, and why isn't there always an easy solution?

What Causes a Misfire? 

A complete combustion cycle requires fuel, air, spark (or timing), and compression. Your engine won't run without the proper gasoline and oxygen mix, and that mixture won't ignite without a spark at the right moment. Compression can be a more complex topic, but it's enough to understand that your engine will run poorly if one or more cylinders cannot maintain the correct compression ratio.

Misfires typically occur when one (or more!) of these elements is missing. For example, a weak or poorly timed spark may prevent the air-fuel mixture from igniting. Low compression in one cylinder can also cause a misfire by reducing the density of the mixture and ultimately allowing your engine to extract less power from combustion.

Your engine relies on precise combustion timing in each cylinder to provide smooth, even power delivery. As a result, it's usually easy to notice when a cylinder is misfiring since the car will run poorly. Even an intermittent misfiring problem can cause noticeable drivability issues, and your check engine light will usually illuminate.

How Do Mechanics Diagnose Misfires?

Unfortunately, a check engine light or noticeable symptoms aren't enough to narrow down the issue. Misfires can occur for reasons as simple as worn spark plugs and faulty ignition coils or as complex and costly as fuel injection issues and internal engine damage. Your car's computer may store additional error codes to help the diagnostic process, but this extra information is not always available.

Mechanics will typically start by scanning for additional codes and, if nothing else pops up, move on to check your spark plugs and ignition coils. These two components are often the easiest to check and replace, making them a good starting point. Following these diagnostics, performing compression tests or looking for fuel system problems, such as fouled injectors or a faulty fuel pump, may be necessary.

Ultimately, the issue is that misfires are a symptom rather than a problem in and of themselves. Diagnosing the underlying cause of a misfire often requires extensive detective work, experience, and sophisticated scanning tools. 

For help with your car problems, contact a car repair service.