8 Causes of Car Engine Sputter

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.

8 Causes of a Sputtering Car Engine

  1. Faulty spark plugs
  2. Clogged fuel filter
  3. Faulty Fuel Pump
  4. Vacuum or intake leak
  5. Dirty or damaged mass airflow sensor
  6. Dirty fuel injectors
  7. Faulty catalytic converter
  8. Faulty oxygen sensors

These are the different reasons which could cause a sputtering engine.

Here is a more detailed list of the most common causes of car engine sputter.

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 with 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.

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 services, it may need a replacement. Fuel filters are most often easy to replace and do not cost too much.

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.

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.

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.

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 clean it with electronic cleaner.

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.

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 come parts lose inside of it which will block the exhaust 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.

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 are no longer can 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.

Written by: Magnus Sellén

Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.