8 Reasons Why Your Car Engine Is Sputtering And How To Fix It

A sputtering engine when stopped or during acceleration can be really annoying. Here's what causes it and how you can fix it

Car Engine Sputter

Driving should be smooth, but if you drive and your car’s engine starts sputtering, the first cause of concern may be low fuel.

However, if your fuel gauge is full, it could be a symptom of further engine problems. For example, a blocked fuel filter could prevent fuel from reaching the combustion chambers.

If the problem is not corrected immediately, it can lead to further engine damage. But, what are the causes of a sputtering car engine?

8 Causes of a Sputtering Car Engine

The most common reason why your car engine is sputtering is because of an issue with the fuel system. This can be caused by a bad fuel filter, fuel pump, or fuel injector. It can also be caused by spark issues from bad spark plugs or ignition coils.

While these are not all possible causes, it’s a good start. Here is a more detailed list of the most common causes of car engine sputter.

1. Faulty spark plugs

Wet Spark Plug

Spark plugs are vital to providing the necessary ignition for the air/fuel mixture. However, plugs wear out and can no longer function as intended.

In this case, you will have lots of unburnt fuel, which causes misfires and the engine to sputter. The spark plugs should most often be replaced after a fixed schedule to prevent things like this from happening. However, if you haven’t replaced them at the time, they should be – faulty spark plugs can cause your engine to sputter.

Remove and visually inspect your spark plugs; if they look ancient and dirty, it may be time to replace them. You should also consider checking the ignition coils, which could cause the same issues.

2. Clogged fuel filter

Dirty Fuel Filter

The fuel filter‘s job is to filter the fuel going to the fuel injectors and then enter the engine. A clogged fuel filter can cause the engine to get too low fuel pressure or cause a clogged fuel injector.

Low fuel pressure will cause the engine to run very leanly, and therefore, it may cause the engine to sputter.

The fuel filter should be replaced after a schedule, and if you haven’t done so during the last service, it may need a replacement. Fuel filters are most often easy to replace and do not cost too much.

3. Faulty Fuel Pump

Cars Fuel Pump

The same thing applies to the fuel pump as the fuel filter. If the fuel pump gets bad, it will cause the fuel pressure to drop very low, which can cause the engine to run too lean.

The easiest way to determine this is to install a temporary manual fuel pressure gauge to the fuel pressure rail and check the fuel pressure on idle and when you rev up.

If your fuel pressure is too low, there is definitely something wrong with either the fuel filter or the fuel pump.

4. Vacuum or intake leak

Cracked Engine Vacuum Hose

If there is a leak around the intake manifold or at the hoses from the intake manifold, it may cause a too lean mixture, which will cause your car engine to sputter on idle.

The easiest way to find this is to use an EVAP smoke machine. However, it is doubtful that you have one at home, so you can also try to find leaks by listening to high-pitched noises around the engine bay when the engine runs on idle.

You can also spray soap around the intake hoses to see if you can notice any leaks.

5. Dirty or damaged mass airflow sensor

Cleaning Maf Sensor

The combustion chamber requires the right amount of fuel and air. Modern engines have an onboard computer that monitors the flow of these components. The mass air flow sensors ensure that the right amount of air is supplied to the combustion chambers.

When the sensors get saturated with dirt particles, they can no longer relay the ECU’s right information. This will cause the engine control unit to spray too much or too little fuel into the cylinders, which will cause the engine to sputter.

You can clean the mass airflow sensor by removing it and carefully cleaning it with an electronic cleaner.

6. Dirty fuel injectors

Fuel Injectors

The fuel injectors play the role of spraying fuel into the combustion chambers on each cylinder. This is then mixed with air and ignited by the spark plugs.

The fuel injectors have small filters inside them, getting clogged if the fuel filter is not doing its job properly. This can cause the fuel injector to spray too little fuel into the combustion chamber, which will cause the cylinder to misfire and may cause the engine to sputter.

These small filters are replaceable, and any workshop should be able to replace them for you.

7. Faulty catalytic converter

Clogged Catalytic Converter

The catalytic converter plays a vital role in removing harmful gases from the exhaust. The catalytic converter gets clogged if it is too old, and it can also happen that parts come loose inside of it, which will block the exhaust’s way.

This will cause too high backpressure to your engine, which will cause the engine to start sputter.

You can use a catalytic converter cleaner to try to clean the catalytic converter.

When your catalytic converter is not working well, you will notice a strong smell of rotten eggs.

8. Faulty oxygen sensors

Oxygen Sensor

Most modern cars have an onboard computer that monitors all the engine components. Connected to this are oxygen sensors that are responsible for the regulation of fuel into the combustion chambers. A faulty oxygen sensor will cause a rich or lean mixture.

With time, the oxygen sensors become contaminated with dirt, and they can no longer relay the correct information to the onboard computer. This causes them to release too much fuel or too little fuel.

To diagnose the oxygen sensors, you need a diagnostic scanner.

Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.

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