Is Your Engine Misfiring? Here are 6 Possible Causes

An engine misfire results from incomplete combustion (or zero combustion) inside one or more cylinders.

But to you, the problem will usually feel like hesitation or shaking when the car is running. In modern vehicles, the Check Engine Light will also pop on when there’s a misfire.

But what exactly causes an engine misfire? And how do you fix it?

Why Is My Engine Misfiring? (6 Common Causes)

There are many reasons why your engine might be misfiring — ranging from a defective sensor to a fuel injector malfunction.

Here are some likely culprits behind a misfiring engine:

1. Ignition System Problems

When most people hear the term ignition misfire, they think of worn-out ignition spark plugs. However, spark plugs are just one part of the ignition system.

A typical modern ignition system contains various components, including the control module, crankshaft position sensor, ignition coil packs, spark plug boot, spark plug wire, and spark plug.

Each engine combustion cylinder has an ignition coil pack (or coil packs that serve two cylinders) that sends electricity to the spark plug, which then ignites the air-fuel mixture.

Issues with any of these components can result in an ignition misfire.

2. Air and Fuel Delivery Problems

The fuel system stores and supplies fuel to the engine, which is ignited by the spark plugs.

The fuel pump draws gasoline from the fuel tank and supplies it to the fuel injectors. The gasoline passes through fuel lines and the fuel filter before reaching the fuel injectors.

Air and fuel mix inside the combustion chamber and are ignited by the plug. The resulting explosion sets the engine in motion, creating the rotational force needed to propel your car.

But, sometimes, a clogged fuel injector, fuel pump, fuel filter, or a vacuum leak in the fuel lines can throw off the air-fuel mixture. This could lead to low fuel pressure — resulting in a misfiring engine.

3. Emissions Equipment Problems

In addition to the catalytic converter, modern cars have an array of emissions equipment to minimize the amount of pollution released into the atmosphere.

These include oxygen sensors, the exhaust gas recirculation (EGR) system, and the positive crankcase ventilation (PCV) system. In some cases, issues with one of these emissions equipment can alter the engine’s air-fuel mixture enough to cause a misfire.

4. Engine Mechanical Problems

Sometimes an engine mechanical problem can cause a mechanical misfire.

Each cylinder inside the combustion chamber contains a piston that compresses the airfuel mixture for complete combustion. When the piston moves upward, the cylinder must remain completely sealed off to create adequate compression.

Internal engine problems that prevent the cylinder from sealing properly could lead to a loss of compression and cause a mechanical misfire.

5. Sensor and Module Problems

Modern vehicles contain several sensors, which the PCM (Powertrain Control Module) uses to control critical functions, such as fuel delivery, fuel pressure, spark timing, etc.

As such, sensor problems can easily contribute to an engine misfire. Also, a problem with the PCM itself can cause a misfire.

6. Control Circuit Problems

All input and output engine management devices (i.e., sensors, ignition coil packs, etc.) are connected via electrical circuits. Problems within these circuits, such as damaged wiring or a loose connection, can cause engine misfires.

You now know what could cause your engine to misfire.

But knowing what an engine misfire feels like can alert you to the problem quickly.

What Does An Engine Misfire Feel Like?

Firstly, remember that you could be driving at any speed when a misfire kicks in, and what your engine misfire feels like depends on what’s causing it.

Here are some common signs you might notice:

A. Loss of Power

As you drive, a misfire can cause the engine to lose power intermittently, or you’ll feel a brief hesitation in acceleration on pressing the throttle.

The engine may also feel like it’s stumbling for a few seconds before regaining pace. This can be the result of an incorrect air fuel mix or low fuel pressure due to a faulty O2 sensor.

B. Jerks or Vibrations

A misfiring cylinder can unbalance the engine, causing a shaking sensation. As the engine misfires and loses power, it may jerk or vibrate aggressively.

Your vehicle may seem to run normally most of the time, but it can struggle to idle when you stop at a stoplight or as soon as you start your car. Any sign of a rough idle is a fair indicator that your vehicle’s fuel system is causing a misfiring engine.

C. Engine Stalls

Stalling can occur more frequently with misfires if you use the air conditioner or headlights. Some misfires will allow you to keep driving (albeit with a fair degree of difficulty), while others will cause your engine to stall completely.

In addition to these sensations, an engine misfire can cause some unique and noticeable sounds in your engine.

What Does An Engine Misfire Sound Like?

When a misfire occurs, you may notice a distinct sound from the engine. It can come either from inside or outside the vehicle, or from the exhaust.

The most common descriptions of an engine misfire are a sound like a popping, sneezing, banging, chuffing, or a backfire, usually when the engine is anywhere between 1,500 – 2,500 rpm.

The sound happens when unburnt fuel exits a misfiring cylinder and is pushed out during the exhaust stroke before being ignited by the spark of the next cylinder. This causes it to explode out through the exhaust system.

You can also identify an engine misfire if it sounds like your car is struggling. An overall change in engine sound can be an indication that one cylinder is not working.

Are there other obvious symptoms of an engine misfire?

Other Symptoms of a Misfire

Besides the obvious sound, you can confirm a misfire if your vehicle has:

• A Flashing Check Engine Light: A flashing engine light is much more serious than an illuminated Check Engine Light, and you shouldn’t keep driving if you spot one. When a flashing or blinking engine light shows up on your dashboard, it’s almost always related to engine misfires. If you ignore the Check Engine Light, it could damage the catalytic converter or, in the worse case, start a fire.

• Black Smoke From Exhaust: When your engine misfires, you might notice a cloud of thick, black smoke from the exhaust. This is often a sign that your engine is not passing fuel and air correctly and could be misfiring.

Next, let’s find out how to diagnose and fix engine misfire troubles.

How to Diagnose and Fix an Engine Misfire?

Since engine misfires are a serious concern and several factors could cause one, it’s best to have a professional mechanic diagnose and fix the underlying issue.

One of the first things a mechanic will do is to check for Diagnostic Trouble Codes (DTCs).

When your car misfires, the ECU (Engine Control Unit) registers a related DTC code and triggers the Check Engine Light. While the engine light and these codes won’t tell the mechanic exactly what’s wrong with the vehicle, they can point them toward the problem causing the misfire.

For example, an engine misfire code might indicate a problem with a specific cylinder or that the engine is running lean (lean misfire). Depending on the diagnostic tool being used, it may show how many misfires occurred within a certain number of cycles or the engine RPM when the misfire occurs.

Here are some of the codes that may indicate a potential misfire:

• P0100 – P0104: Mass airflow sensor

• P0171 – P0172: Lean or rich fuel mixture

• P0200: Fuel injector circuit malfunction

• P0300: Random misfire that’s not isolated to one or two cylinders.

• P0301: Misfire in engine cylinder 1

• P0302: Misfire in engine cylinder 2

• P0303: Misfire in engine cylinder 3

• P0304: Misfire in engine cylinder 4

• P0305: Misfire in engine cylinder 5

• P0306: Misfire in engine cylinder 6

• P0307: Misfire in engine cylinder 7

• P0308: Misfire in engine cylinder 8

However, not all misfires will cause a DTC to be logged, particularly if there’s an intermittent misfire. If a misfire code doesn’t help, your mechanic will typically begin by inspecting the spark plugs. If a plug appears damaged or if the spark plug is old, replacing it may solve the issue.

Next, the mechanic will perform a compression test to check if your air, fuel, and spark systems are all in order. If the issue is related to compression, they may perform a repair, such as replacing the head gasket.

Note: Replacing the head gasket is a complex job and is best left to expert technicians.

Finally, if there are no compression issues, the issue could be the coil pack. They’ll use a multimeter to test the coil pack resistance and replace it if needed.

With the misfire diagnosis and fixes under your belt, let’s answer some common queries.

4 FAQs on Engine Misfires

1. What Is an Engine Misfire, and When Does It Occur?

For your engine to fire its cylinder, it needs fuel to burn, oxygen to facilitate the burn reaction, and an ignition spark to get things going. If any of those elements are not present at the perfect time, the cylinder won’t combust, causing a misfire.

Misfires are of three types:

• Dead-miss: A complete misfire with no combustion taking place at all.

• Partial misfire: When there’s some kind of a burn but significantly incomplete combustion.

• Intermittent misfire: Occurs only sometimes, under certain conditions or indiscriminately.

Misfires can occur both during engine startup and while accelerating.

A. Misfire During Acceleration

Misfires can happen when a vehicle is under load while accelerating. The most common cause of rough acceleration due to misfires is worn-out spark plugs, a cracked distributor cap, a bad spark plug wire, or a failing throttle position sensor (TPS.)

In addition to the engine misfire, the Check Engine Light will come on, and the vehicle may even go into ‘limp mode.’

B. Misfire at Idle Only

Your car may drive perfectly fine but display signs of little hiccups or small misfires at idle.

Generally, the cause of a misfire at idle is an incorrect air-fuel mixture. This can be caused by a faulty O2 sensor, a fuel injector that needs cleaning, or even vacuum leaks.

2. What Should I Do If My Engine Misfires?

If you suspect your engine is misfiring and you aren’t driving your vehicle, make an appointment with a technician ASAP. Get your vehicle inspected and repaired to prevent further damage.

If you experience an engine misfire while you are on the road, slowly get to safety first and try to cruise your vehicle to the roadside. Turn off the engine and get your car towed to a repair shop or call a mobile mechanic.

Before the mechanic takes a look at your vehicle, try to collect as much information as you can, including any peculiar sounds or unusual behavior. Also, note under what circumstances the engine misfired and how frequently you notice the signs. The more information you have, the easier it will be for your mechanic to find the cause of the misfire.

3. Is It Safe to Continue Driving with an Engine Misfire?

Technically, yes. But it’s strongly advised that you don’t.

Instead, you should get your car inspected at the earliest.

However, if your engine misfires and you notice a blinking Check Engine Light, stop driving immediately and call for roadside assistance.

If your engine misfires and you continue driving, not only is it a potential safety hazard, but you can also damage a costly engine component, like the catalytic converter. The heat generated by a misfire can also warp or crack valves and the cylinder head.