Why Is My Car Misfiring – What To Do

What is an engine misfire?

In an engine with ignition initiated via spark plugs, the mixture of fuel and air inside each cylinder is ignited by a spark from the spark plug. The resulting explosion drives the piston downward, turning the crankshaft and ultimately powering the vehicle’s wheels. A car misfire is when the engine doesn’t fire on all cylinders. It occurs when the air-fuel mixture in the cylinders fails to ignite. This can cause the engine to run rough and may even cause it to stall.

A misfire can be caused by a variety of things, such as a spark plug that is not firing, a fuel injector that is not working, or a problem with the timing belt. When an engine misfires, it can cause a number of problems. The most obvious is a decrease in power and performance. An engine that is misfiring will often feel “rough” and may hesitate or stall when accelerating. Misfires can also cause increased emissions and decreased fuel economy.

In some cases, an engine misfire can also cause damage to the catalytic converter. The converter is a device that helps to reduce emissions by converting pollutants into less harmful substances. A misfire can cause unburned fuel to enter the converter, which can then overheat and get damaged.

Why is my car misfiring? Common causes:

1. Ignition system problems

Worn-out spark plugs can cause an engine to misfire because the spark plugs are not igniting the fuel in the cylinders. This causes the engine to run rough and can eventually lead to engine damage. Other ignition components that can fail and can result in a misfire include ignition coil packs, wiring and sensors.

2. Fuel system problems

Dirty or clogged fuel filters can limit the flow of fuel causing a misfire. A failed fuel injector is mostly due to build-up of contaminants which can prevent the injector from opening or closing all the way thus resulting in a car misfire.

Sometimes, if there is an issue with the fuel pump where it’s not able to maintain the required pressure for the fuel injectors, it can also lead to a misfire.

3. Compression problems

Low compression in the cylinders can be caused by holes in pistons, leaky valves and even a leaky head gasket. When this happens in one or more cylinders it can affect engine performance as you’re driving and if it happens to all cylinders it can cause the engine not to start.

4. Exhaust system problems

An exhaust leak or blockage is a major cause of misfires. If there is an exhaust blockage, then the engine is not able to expel all of the exhaust gases. An exhaust leak can cause the engine to run rich because there is too much oxygen being drawn into the mixture. A rich or lean mixture can cause misfires.

5. Vacuum leaks

An air intake vacuum leak can cause an engine misfire because it allows air to enter the engine, which throws off the air-fuel ratio. This can cause the engine to run lean, which can cause misfires.

What are the symptoms of an engine misfire?

Loss of power

One reason is that if an engine is misfiring, it is not operating at peak efficiency. This means that the engine is not able to produce as much power as it would if it were operating correctly. Additionally, a misfire can cause damage to the engine itself, which can lead to a loss of power.

Illuminated Check engine light

There are many sensors on modern vehicles that are constantly monitoring the performance of the vehicle. The engine control unit (ECU) is notified if a sensor detects a problem with the engine. Whenever a serious problem is detected such as an engine misfire, the Check Engine light will illuminate or flash, informing you that action needs to be taken to fix the problem.

Decrease in fuel efficiency

When an engine misfires, it is not able to convert all of the fuel into energy. That means there is wasted fuel that does not get used. When there is wasted fuel, the fuel efficiency of the engine decreases.

Increase in emissions

An engine misfire can result in increased emissions due to the incomplete combustion of fuel in the cylinders. This can cause an increase in hydrocarbon and carbon monoxide emissions.

Black smoke from tailpipe

When your engine misfires, it might produce a cloud of black exhaust, which indicates that fuel and air are not being passed properly. You may be experiencing a misfire if your vehicle emits exhaust in this manner.

Engine noises

A misfire can cause unique and distinct engine noises because the engine is not firing on all cylinders. This can cause the engine to run rough and make a knocking, sputtering or backfiring sound.

What does an engine misfire sound like?

An engine misfire will often sound like a choppy, dull thudding or a backfiring noise. The car will shut off the fuel injectors when it senses a misfire and the check engine light will typically illuminate.

You do not have to be an expert to realise your car may be misfiring. It’s likely that your engine sounds different than normal if you listen closely. You may notice that the car is accelerating rougher or slower than usual, as if it’s lost power. The engine may feel like it’s jerking or vibrating for a few seconds before going back to normal.

This YouTube video will give you a rough idea of what an engine misfire feels and sounds like.

My car keeps misfiring, what can I do?

If your car is misfiring while driving and goes into limp mode, you will find that the car is still driveable but will feel “impossible” to handle. This is a sign that something is wrong with one of the many elements that contribute to the smooth running of the engine and cylinders. The best thing to do is get in touch with a local mechanic as soon as possible to carry out a diagnostic to avoid any further damage to the engine.

A qualified mechanic will carry out a diagnostic test to identify the cause for the misfire. In most cases, you will need to get spark plugs replaced, clean fuel filters or replace the fuel injectors, replace the ignition coil or just fix wiring issues.

Is it safe to continue driving with an engine misfire?

While the vehicle may still be drivable, continuing to drive with an engine misfire will cause further strain on the engine causing irreversible damage. It is also a safety hazard because if the second or third cylinder fails while driving, the car will lose power which can cause serious accidents in addition to engine damage.

Diagnosing an engine misfire

You can run a diagnostics tool or a mechanic will use a code reader or OBD-II scan tool to run diagnostics. These codes can help to narrow down the possible causes of the problem.

mechanic doing a diagnsotic


Diagnostic trouble codes P0301 through P0312 are common codes that show up on the plug-in diagnostic tool. The most severe code is the P0300 (it means that one or more engine cylinders are misfiring) where the vehicle should not continue to be driven at any cost as the engine could shut down and the catalytic converter can get damaged without warning. The mechanic will need to inspect the vehicle and find the source of what is causing the misfire and get it fixed.

Another way to diagnose an engine misfire is to have a qualified mechanic perform a compression test. This test can help to identify issues with the cylinders, valves, or pistons.

Book Engine Misfire Diagnsotic