Why Is My Engine Misfiring?

An engine misfiring happens when the combustion breaks down. What are the signs of an engine misfire and the cause, lets find out.

Misfiring is more common with newer or modern engines. If you believe your engine is misfiring, it’s not usually an easy thing to investigate if you don’t know where to start or what you are looking for.

With our guide, we will go over some possibilities that might be causing the problem. To start with, you should know what signs to keep an eye out for.

The most common signs of your engine misfiring are rough acceleration or rough idle. Other signs include a “check engine” light and poor engine performance. In some cases, you will notice the check engine light will blink while the engine is misfiring.

Here is a detailed list of the most common symptoms or signs when an engine misfires:

1- Rough Acceleration

As we briefly touched on. You might experience a strong or light jerking coming from the engine. Misfiring often happens under load from the engine such as when you are accelerating hard. The most common occurrence of misfiring is in high gear, low RPM, or the accelerator is pushed to the floor. This is referred to as Rough Acceleration.

2- Rough Idle

Car Shaking

Sometimes when idling, the engine will misfire caused by the engine sensors that will receive defective values and the air-fuel mixture is messed up. These issues can lead to a very uneven idle which will jump up and down causing a rough idle and in some cases, the engine may literally shut off.

Your engine is most vulnerable when there are small air-fuel mixture problems while idling, so that’s probably the first place you should look into.

3- Vibrations

Your car’s engine is balanced during manufacturing and usually has balanced axles but there are some techniques to get as few vibrations as possible.

When one or more of the cylinders are not firing correctly, the engine will become unbalanced. This can lead to heavy vibrations inside the cabin when accelerating or when idling.

4- Check The Engine Light

Newer cars have excellent monitoring devices for the different sensors on the engine. If a sensor fails or picks up a signal that something is not right with the engine, it will send information to the engine control unit.

After the engine control unit gets the data, it will analyze if the problem is serious or not. If the problem happens several times, the engine control unit will light up the check engine light to let you know that something is not right. That’s when it’s time to get it checked out and fixed.

5- Slow Acceleration

Misfiring can cause the O2 sensors to get incorrect information and generate a mixture that is too rich or overly diluted. A rich or diluted mixture can lower the acceleration making your car seem weak. Your car will not rev over 3500 RPMs and could shut off the boost pressure from the turbocharge.

6- A Change In The Engine’s Sound

Even if you only know very little about cars, you probably have heard a difference in sound from one engine to another. V8 engines have a completely different sound from that of a four-cylinder engine.

If a 4-cylinder engine is misfiring on one cylinder, it could sound like a three-cylinder engine. If the sound is extraordinary, it is probably misfiring on every cycle possible.

The Most Common Reasons Why An Engine Will Misfire

The first reason for a car misfiring is a bad ignition coil or bad spark plug. Another leading problem could be fuel-related such as a poor fuel injector or fuel pump. In some rare cases, it could be a low engine compression.

The following is a list of the most common reasons for engine misfiring starting with the most common reason:

1- A Bad Ignition Coil or Distributor In Older Cars

Bad Ignition Coil

The most common problem is usually the ignition coil. Some cars have a separate ignition coil for each spark plug while other cars have one coil with a sparking cable for each spark plug.

Older cars have a distributor and in some cases an ignition coil. If you have separated spark plugs, unplug each coil and see if you can find any cylinders that are not responsive.

If you find a defective ignition coil, replace it or have a trouble code stored for one ignition coil.

2- A Defective Spark Plug

This is the second leading cause for misfiring. The spark plugs fire up the cylinders and they can get worn out over time. In general, spark plugs are cheap and very easy to replace.

3- Intake Manifold Gasket Leaks

Intake leaks near the cylinder heads are quite common when it comes to spark plugs. This particular problem was a lot more common in older cars without steel gaskets for the intake.

If you do have an older car, you should check for leaks. If you have a newer car, it’s probably worth your time to check other signs of leaks around the intake manifold gasket or the intake. You can also check for broken vacuum hoses.

4- Low Fuel Pressure

Low fuel pressure could be the reason for a faulty fuel pressure regulator, a defective fuel pump, or a clogged fuel filter. Low fuel pressure can lead to a thin mixture in your engine which can lead to misfiring on all cylinders.

If you have trouble codes for misfires on all cylinders, you should definitely check out your fuel pressure.

5- Injector Issues

Car Engine Injector

This was a problem approximately around 2017. A defective fuel injector can cause your engine to misfire and can be rather difficult to diagnose without flow testing them.

Injector issues are not particularly common in newer cars. You should check out other possible issues first then check the injector if needed.

6- Low Compression Or Damage Inside The Engine

If you have checked everything, there is always a chance your engine has low compression or other damage inside it.

A defective timing belt adjustment could cause low compression resulting in misfiring. If you know the timing belt was recently replaced, you should double-check with the technician who installed it.

7- The Wrong Air-Fuel Mixture

Car Air Fuel Mix

If you have an incorrect air-fuel mixture it can cause misfiring. Many different sensors can also cause a poor air-fuel mixture in your car such as the MAF sensor, O2 sensor, Coolant Temperature sensor, or other problems.

What Is A Misfire?

To understand what a misfire is takes going through the car engine basics first and foremost. You need to get a good picture of your pistons and crankshaft to ensure they are moving inside the cylinder when your engine is running. The pistons are pushed down by the explosion inside the cylinder.

When the crankshaft is spinning the piston is pushed down. The engine is working in four steps which is why that engine type is called a four-stroke engine.

This is how it works:

The piston goes down filling the cylinder with an air-fuel mixture and the explosion is pushing the piston down and rotating the crankshaft. The piston goes back up, emptying the burned air-fuel mixture through the exhaust pipe.

That’s how a four-stroke engine works that is found in almost all modern car engines today.

A misfire happens when one or more of these stages are wrong or missing –

A rich or thin air-fuel mixture
Bad ignition spark or wrong timing of the ignition spark
Low compression or the air-fuel mixture is leaking
The timing of the inlet/outlet of the air-fuel mixture is not right

Knowing all this makes it a lot easier to find the culprit that is causing a misfire. In theory, there are not a whole lot of things that could cause misfiring.

When you start diagnosing your car, you will understand that is not always as easy as you might think when looking for the problem.


Understanding how components and devices work in your car gives you the upper hand to fix the problem in a timely manner. If you are not mechanically minded or inclined, contact your technician to get misfire issues investigated , repaired or replaced in order to avoid the issue escalating.

For engine misfire problems in and around Manchester city centre and North Manchester, you can count on Servicing Master. You can get a quick repair quote from a local premium garage close to you by using our simple car repair quote form. We also offer a collection and drop off service. A convenient, friendly and affordable service, try Servicing Master once and you’ll never go back. Give us a call now on 0161 302 0201.

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