Modern car engines don’t flood very often and so your car may be telling you it has a problem.
So how do you fix a car flooded with gas? The best way to fix a gas-flooded engine is to open the hood and wait ten minutes before cranking over the engine with the gas pedal flat to the floor until the engine starts.
When I was learning to drive, flooding an engine was a real day-to-day common hazard, once you smelled that raw gas you knew you were in trouble.
In this post, I’ll show you how to diagnose a flooded engine and how to fix it fast. We’ll also take a look at what can cause the flooding.
What Is “Car Engine Flooded”?
For an engine to run smoothly it needs a fine balance of gas to air, the ratio is known as stoichiometric – 14.7 parts air to 1 part gas, known as AFR (Air Fuel Ratio).
This ratio is the optimum balance and means the engine is burning the fuel completely, which is better for the environment and your fuel economy.
A modern car ECU is constantly adjusting the amount of fuel, so the car engine goes from lean to rich to lean and so you might say the average is 14.7 to 1.
Older cars use a mechanical carburetor to measure and maintain the ratio and modern cars rely on sensors, a computer, and injectors to get the balance just right.
So what is flooding? Flooding is when the ratio gets way out of line – more gas than air, a lot more. So much gas that in really bad cases of flooding, the cylinders can fill causing the engine to hydro-lock (Pistons locked).
Hydro-locked with gas isn’t serious when it happens while only attempting to start the engine – rpm’s (engine speed) is low.
However, you may have heard of hydro-locking in reference to a car being driven through flood water, this, unfortunately, is serious and usually results in bent con-rods (Expensive).
How Can You Tell If A Car Is Flooded With Gas?
The symptoms will vary slightly depending on how badly it’s flooding and why it’s flooding. (more on this later). Generally, flooding occurs on start-up, not when an engine is running. Common gas flooding symptoms include:
- Strong smell of raw gas in the air, you won’t miss it
- Engine won’t start
- Wet spark plugs
- Engine almost starts, and belches a cloud of black smoke from the tail pipe
- Engine starts but misfires for a while when cold
- Engine won’t crank over but battery is OK
- Gas dripping from the engine
- Oil level too high and stinks of gas
If you have a plug socket and ratchet, you can remove the spark plugs and check if they’re wet, then you know for sure the engine is flooded.
Why Do Car Engines Flood?
I was a gear-head from the beginning, as a kid of about nine my father would let me start the car in the mornings (different times). You had to pull out the choke (I can still remember the weight of the Citroen doors) and back it off a 1/4 after the motor started, then back to half, the time it took all depended on how cold it was.
On a frosty morning, I could be out there for fifteen-twenty minutes. I flooded the old Citroen many times, but I eventually got a handle on it.
That was old cars, modern cars have automated choke and you barely notice any difference from cold running to closed loop. So flooding a modern car isn’t that common, in fact, it usually points to a maintenance issue or a mechanical fault.
Let’s take a look at what can cause flooding in a modern car engine:
- Repeated pressing of the gas pedal at start-up
- Contaminated gas
- Blocked air filter
- Bad Maf sensor
- Leaking injectors
- Bad spark plug
- Bad plug wires
- Bad coil
Modern cars are programmed to protect the environment, the ECU’s are designed to detect a misfire (cylinder that didn’t ignite) and shut down fuel to that cylinder, but it is possible for the misfire to go undetected.
It’s important to shut down fuel to a cylinder that’s not firing as excessive raw fuel will:
- Wash protective oil from the cylinder
- Leak into the crankcase diluting the oil
- Damage catalytic converter
- Bad for environment
- Bad for your gas mileage
How Do You Start A Flooded Engine?
If you suspect that your engine is flooded, getting it running is a simple procedure. In most cases, you won’t even need any tools.
Secret Tip – Modern ECU’s are programmed to stop fuel flow to the injectors while the gas pedal is pressed to the floor and held there while cranking the engine over. This opens up the airway to the engine and helps dry out the plugs and cylinders.
Most owners don’t know about this hack, so pass it on.
Here’s the four step procedure:
This procedure works for both old cars and modern computer-controlled fuelling systems.
Poop the hood – this helps the gas to evaporate quickly.
Take a coffee break – this gives the raw gas in the cylinders time to evaporate.
Put your accelerator flat to the floor.
Turn the key until the engine starts. (Don’t crank the engine for more than one minute constant).
If you need to repeat step four, do so without any accelerator this time.
If the flooding reoccurs, buy an inexpensive fault code reader and check the engines for fault codes.
What happens if water enters the engine? When water enters the engine it fills one or more of the combustion cylinders, and since water isn’t compressible, the piston con-rods usually bend. The engine may still run but will idle erratically.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.