What happens when you flood an engine

Sunday 17th September 2023

Flooding an engine happens when there is an excessive amount of fuel in the engine's combustion chamber. This guide will explain what a flooded engine means, along with the reasons why this could happen and how to fix it. Here at Formula One Autocentres, our expert team are ready to help diagnose and repair almost any vehicle issue.   

What does a flooded engine mean?

In simple terms, a flooded engine means that there's too much fuel in the engine's combustion chamber, making it hard to start the engine. The excess fuel prevents the mixture of fuel and air needed for ignition, meaning, if the engine is flooded, you’ll have trouble getting the engine to run smoothly or even start at all. 

Can you flood a diesel engine?

Yes, you can flood a diesel engine. Even though diesel engines are built differently compared to petrol engines. If the combustion chamber has been overfilled with diesel fuel it will struggle to ignite causing the same issues with starting your engine or keeping it running as you would with a petrol car. 

How does an engine get flooded?

There are several reasons that can cause an engine to flood, from the way you start the car, to several underlying issues. Some of the main causes of engine flooding include: 

• Pumping the accelerator: Pumping the accelerator pedal when starting the car can introduce too much fuel into the combustion chamber, making it difficult for the engine to ignite properly. 
• Cold weather: Starting your car in freezing temperatures can affect the fuel’s ability to turn into vapour, causing more liquid to pool in the combustion chamber, making it harder to start the engine.  
• Sensor issues: A faulty oxygen sensor can cause the engine control unit to deliver more fuel into the combustion chamber than necessary.  
• Leaky fuel injector: If your fuel injector is leaking it can end up continuously dripping fuel into the combustion chamber, even when the engine is off which can cause flooding.  
• Ignition system issues: Faulty spark plugs, ignition coils, or other ignition system components can lead to unburned fuel accumulating in the combustion chamber. 
• Clogged Air Filters: Clogged air filters restrict airflow, potentially stopping the air from reaching the fuel and flooding the engine. 
• Fuel System Problems: Issues with the fuel pump, fuel pressure regulator, or fuel lines can result in excessive fuel entering the combustion chamber. 
• Stalling and Restarting: Sometimes, when an engine stalls and is immediately restarted, the combustion chamber can still be full of fuel, causing flooding. 

How to fix a flooded engine

To fix a flooded engine the excess fuel needs to be cleared from the combustion chamber to allow your car to reset. Follow these simple steps to fix a flooded engine. 

1. Turn off the ignition 
2. Let the engine sit for a few minutes 
3. Fully depress the accelerator to clear the flood 
4. Start the engine with the accelerator pedal down 
5. Let the engine run for a few minutes to burn off the remaining excess fuel 

Prevent flooding your engine with a regular service

Booking your car in for a regular service, either every 12,000 miles or 12 months, whichever comes first, can help to prevent some of the issues that cause engine flooding. Our full service includes checking and replacing the air filter if it’s clogged as well as providing a full inspection of your exhaust system, fuel system and making sure all fluids are at the correct level.  

Our professional mechanics are trained to identify any early signs of potential issues that could lead to flooding and help the problem from escalating. Ready to book your car in for a service? Book now. Or for more information, contact a member of our specialist team today.