How Do I Know Whether My Engine is Misfiring?

Engines can misfire at any point. There isn’t always any warning, and it doesn’t only happen when you turn your engine on.

You could be driving smoothly at any speed when engine misfiring kicks in.

While some engine misfires are easy to diagnose, others are notoriously challenging, especially if the misfiring is intermittent.

The Importance of Understanding Engine Misfiring

An engine cylinder misfires when it can’t burn the air-fuel mixture in the combustion chamber. As the engine loses power, it jerks aggressively, dramatically raising your fuel consumption and emissions output.

Misfiring usually occurs when an engine component is excessively worn or damaged. The good news is that most of these parts are easily accessible and can be self-serviced with a little know-how.

If your engine is misfiring, it’s important to diagnose the fault as soon as possible. The longer you leave it, the more fuel you will waste, the more toxic emissions you will release into the atmosphere and the more likely it is that the damage will spread to core engine components.

Note: it’s not safe to drive long distances with a misfiring engine.

Symptoms of Engine Misfiring

These are the signs of a misfiring engine that you need to look out for:

• The engine loses power
• It is difficult to start the engine
• Fuel consumption rises
• Emissions increase
• The engine makes popping sounds
• The intake or exhaust manifold backfires
• The engine jerks, vibrates or stalls

Diagnosing Engine Misfiring

You can use a scan tool or code reader to diagnose engine misfiring. These tools retrieve data from your vehicle to identify the cause of the misfires. Scan tools and code readers identify:

• The cylinder(s) where the misfires are occurring
• Whether the cylinder(s) has fired since the misfires were detected
• How many misfires have occurred within a recent number of cycles
• The engine RPM when the misfire was identified
• The misfire history

Answering the following questions will also help you to identify the cause of the engine misfiring:

• Does the engine only misfire when it is cold/warm?
• Does the engine only misfire when you are accelerating?
• Does the engine only misfire when it rains?
• Does the engine misfire randomly?

What Causes a Cylinder to Misfire?

Engine misfiring is typically the result of one of three issues: loss of spark, an improperly balanced air-fuel ratio or loss of compression. In each of these instances, one or more of the cylinders fails to fire, stunting the combustion process.

A misfire can happen as a result of:

• A component failing in the ignition system
• A problem in the fuel system
• Vacuum leaks
• A compression drop in at least one of the compression cylinders
• Damaged valves and/or sensors that calculate air-fuel ratio
• Damaged spark plugs

Engine Misfiring and Spark Plugs

Misfires due to lack of spark are especially problematic as unburned fuel can enter the exhaust system and destroy the catalytic converter. Look out for the engine light or malfunction indicator light on your dashboard – at least one of these will flash if your catalytic converter is at risk of damage.

A diagnosis can often be made quickly if the cause of the misfiring is the spark plugs. Worn spark plugs can be replaced easily at a low cost. Check that you have the right spark plugs for your car, that the plug gaps line up with the recommended gaps in your vehicle handbook and that the spark plugs are in good condition.

Our blog post, ‘How to Know What Your Spark Plugs are Telling You’ shows you how you can determine the condition of your spark plugs. Find it here.

If you need new spark plugs, you can enter your number plate into our car look-up tool to access all the spark plugs that will fit your vehicle.

DIY Car Service Parts stocks spark plugs from an array of reliable OEM and aftermarket brands, offering the best prices on the spark plug market.

Engine Misfiring and Other Car Parts

Aside from your spark plugs, your spark plug wires, ignition coil, ignition control module, distributor or ignition timing could also be faulty. These are the car parts that are affected when the spark plug can’t produce enough spark for combustion.

If the engine misfiring is the result of fuel supply problems, a clogged fuel filter, contaminated fuel, leaking fuel injector or faulty fuel pressure regulator could alternatively be the cause of your engine misfiring.

If loss of compression is causing the engine misfiring, the damage could be the result of a damaged vacuum hose, PCV valve, EGR valve, the pistons or the sensors.

Avoiding Engine Misfiring

Servicing your car vastly reduces your risk of engine misfiring.

Luckily, with the help of DIY Car Service Parts, you can maintain your car, troubleshooting and performing small maintenance jobs easily and at a low price. Regular checks on your filters, spark plugs and other service parts will help to keep your car healthy long-term.

To build your service parts kit, enter your number plate into our car lookup tool to find all the car service parts that will fit your vehicle.

All DIY car service parts are manufactured by trusted, high-quality brands. Here are just a few of the brands that we stock.