A flooded engine seems to be a problem of the past.

Thanks to modern fuel injection technologies in collaboration with other modern systems its seem to be solved for good.

Nevertheless, it still does happen although mostly on high-mileage, used cars where the fuel intake system isn’t in its prime condition anymore.

Also, these problems are common in older cars where there is a carburetor instead of a fuel injection system. Old-timer owners will know what I mean.

Whatever the case may be, this article should shed some light on the whole problem and perhaps offer a solution.



Before we start, it’s probably good to know what a flooded engine exactly means.

You see, the internal combustion engine is highly dependant on a correct air-fuel mixture.

Besides that, how fuel gets into the combustion chamber is very important. It’s supposed to be a fine mist and in case of fuel injection systems, highly pressurized.

If the engine is provided with a very rich air-fuel mixture which is poorly injected into the combustion chamber, it can’t be ignited by the spark plug.

Simply, the mixture splashes the spark plug and engine cylinder making combustion impossible.

Hence the expression FLOODED engine.

For a more thorough explanation of the flooded engine definition provided form Wikipedia, click here.




  • Faulty or worn out spark plugs

If the spark plugs are worn out or damaged, they won’t produce an instantaneous strong spark.

This will then lead to a flooded engine as the air-fuel mixture won’t be ignited properly or at all.

  • Faulty fuel injectors (for fuel injection systems)

Fuel injectors are in charge of injecting fuel under high pressure into the combustion chamber.

Although they’re made out of highly durable metal materials, an aggressive substance like fuel, injected under high pressure will damage them over time.

When damaged, the fuel injector produces a thin stream of fuel instead of a fine mist (pardon the comparison: the injector ˝spits˝instead of ˝sneezing˝fuel).

This leads to flooding the engine because the air-fuel mixture doesn’t have the necessary quality.

Also, the fuel will splash the spark plugs and cause them to malfunction.

  • Bad carburetor or one that is poorly adjusted(for older type cars)

The carburetor is a device that mixes air and fuel to produce the proper mixture for the inner combustion engine.

If the carburetor is faulty (weak or damaged nozzles, damaged gaskets, a punctured float, or else), it can easily cause a very rich mixture and a flooded engine.

Also, poorly adjusted carburetors can cause the same problem.

  • A rich air-fuel mixture ratio

Too much fuel in the air-fuel mixture will cause a flooded engine.

As mentioned, a rich mixture in cars with a carburetor may be caused by faulty or damaged parts or if it’s poorly adjusted.

But with fuel-injected systems, it’s more complicated. Besides faulty fuel injectors, other reasons for a flooded engine may be bad sensors (O2 sensors, MAF sensors, etc), a faulty electronic control unit (ECU), or else.

  • Problems with other parts of the ignition system

Besides spark plugs, there might be problems with ignition coils, cables, connections, sensors, distributors, or even the ECU unit.

All of this will lead to a weak or non-existing spark meaning the mixture enters the combustion chamber but doesn’t ignite.

  • Starting and stopping the engine in a short notice

This reason is mostly due to bad driving habits and lack of experience.

A problem like this mostly happens during the winter season and in urban driving.

In these conditions (especially in winter) the engine struggles to reach working temperature and the fuel has a higher density.

Combine this with frequent stops and starts and you might easily get a flooded engine.



  • A strong smell of gasoline

This is usually the first and most obvious symptom.

Depending on how severe the problem is, it may appear as a slight odor or have an intensive smell that will even reach the passenger cabin.

  • Very fast cranking

When cranking, the engine sounds like there’s a lack of compression.

This usually happens if the mixture is saturated with fuel or if the driver is persistent to start the car over and over again without any success.

  • Car won’t start at all

This is the final phase of the problem.

It may be preceded by a short sign of ignition before totally giving in.

After this, the usual situation is that you won’t be able to start the car at all (just cranking, no starting).



On this part it’s best to divide the solution depending on whether the car has a fuel injection system or a carburetor:



  • Believe it or not, the best thing to do is….wait

Leave the car alone for at least an hour and try to ta start the engine again. The surplus of fuel inside the cylinder tends to naturally evaporate and the spark plugs may dry up a bit. This increases the chance for a successful engine start.

Also, with this option, you’ll have the least fuss in terms of repairing or even towing.

It’s certainly worth the try.

Don’t hesitate to give the car a longer crank if the battery isn’t depleted. If you hear that the engine is ˝willing˝to start, then you may be on the right path.

If this doesn’ help then there’s a probably bigger issue.

At this point, you can choose two paths:

  • If you don’t have any experience around cars best call help and towing service. Better this than cause more trouble, like damaging the car battery or starter.

If you know your way around the car and provided you have the means then you can do the next things:

  • Connect a diagnostic tool to the car (Onboard Diagnostic Tool-OBD)

As mentioned, with modern injection systems there can be an array of problems causing a flooded engine.

An OBD tool should give you a head start where to look for the problem. For instance, if a sensor of some sort is faulty the tool will provide an error code.

Although not always the solution, it may shed some light on the problem and spare you from unnecessary repairs, dismantling, or ending up in a dead lane after a couple of hours.

  • Change or clean the spark plugs

If waiting for the fuel to naturally evaporate didn’t help, then best take off the spark plugs and clean them thoroughly.

This may be a problem on some cars as the spark plugs may be hard to access or you’ll need special tools. Check this out before you start so you don’t get into trouble.

One more benefit of this procedure is that, once the spark plugs are out, the excessive fuel in the cylinder will evaporate more quickly and increase the chances for an easier start.

Best use a wire brush, fine sandpaper, and some cloth to dry and clean them properly.

If they are on their last legs or soon due for replacement, then best change them right away.

More on the spark plug topic in a separate article which you can read by clicking here.

  • Press the gas pedal to the floor when cranking the engine

This should give more air into the air-fuel mixture and make starting the engine easier.

It may or may not help, all depending on the car model and fuel intake system.

Definitely worth the try and won’t cause any harm.

  • When the engine starts, let it warm up for at least five minutes while occasionally pressing the accelerator pedal

This will eliminate any leftover residue on the spark plugs as well as enable the ECU to read new information if some repair was done.



Here problems are much more mechanical in nature and maybe not that complicated to solve.

Also, a flooded engine, in many cases, is caused by a driver’s lack of experience and knowledge in driving cars with carburetors.

Unlike injection systems, here you don’t have tip-toe a lot when repairing and you can take concrete measures and perhaps solve the problem right away.

  • Waiting

With carburetors, this is also an option. Leave the car for about an hour and then try starting it. If you can’t make any repairs due to a lack of knowledge or the current circumstance, this is the best option.

It may work if the flooded engine is caused accidentally by the driver. If something else is wrong, it may not help.

  • Clean or replace the spark plugs

If you can, take the spark plugs out immediately and clean or replace them.

There’s a good chance that the spark plugs on older type engines are accessible and that a basic spark plug tool will do the job.

Pretty much a routine procedure and if you have even the slightest knowledge around car repairing, you should be able to do it.

While the spark plugs are out, fuel will evaporate from the cylinders making it much easier to start the engine.

  • Check that the choke valve is open

The choke is a valve installed inside the carburetor. It’s in charge of restricting the airflow and thus richening the air-fuel mixture. Its main purpose is to make a cold engine start easier.

The choke valve is either manually operated (with a cable) or automatically (electrically or with a bimetal).

When the engine is flooded, the choke valve should be in the open position letting in the maximum amount of air. This way the air-fuel mixture is leaner making it easier to ignite.

With manually operated chokes, it’s easily done by just pushing the cable knob in to release position.

On automatic ones, best take of the air filter housing and see that the choke plate is open on the carburetor.

  • Check that the rest of the ignition system is OK

While you’re at it, also check the spark plug cables, connections, distributor cap, and else.

  • Start the engine with the accelerator pedal pressed to the floor

Once you’ve returned everything in place, press the pedal to the floor and start cranking.

Don’t pump, just press once and hold it like that.

The usual scenario is that the engine will start momentarily and then cut off. One or more additional crankings and the engine should start normally.

If the engine doesn’t show any signs of ignition best leave it as probably something more serious is wrong.

  • When the engine starts, leave it to idle for at least five minutes while occasionally pressing the accelerator pedal

This will eliminate any leftover residue on the spark plugs and help return a normal engine function.



For the end, I must emphasize this one more time:

A lot of cranking and gas pedal pumping will not solve the problem of a flooded engine.

Many times I’ve seen people do this only to make things worse and cause even more problems (mainly through damaged car batteries and fried starters).

Lack of knowledge, experience, and patience are the main reasons for this.

This goes double for modern engines. If it doesn’t start until the third cranking, it probably won’t start at all. At least until you try some of these methods.

So, knowing how to react and solve a flooded engine problem may prevent lost time, money, and certainly some lost nerves.



Written by: Sibin Spasojevic


Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com