Flooded engine
Encyclopedia
A flooded engine is an internal combustion engine
that has been fed an excessively rich air-fuel mixture that cannot be ignited. This is caused by the mixture exceeding the upper explosive limit for the particular fuel. An engine in this condition will not start until the excessively rich mixture has been cleared. It is also possible for an engine to stall from a running state due to this condition.
Engine flooding was a common problem with carbureted cars, but newer fuel-injected ones are immune to the problem when operating within normal tolerances. Flooding usually occurs during starting, especially under cold conditions or because the accelerator has been pumped. It can also occur during hot starting; high temperatures may cause fuel in the carburetor float chamber to evaporate into the inlet manifold, causing the air/fuel mixture to exceed the upper explosive limit. High temperature fuel may also result in a vapor lock, which is unrelated to flooding but has a similar symptom.
A severe form of engine flooding occurs when excessive liquid fuel enters the combustion chamber. This reduces the dead volume of the combustion chamber and thus places a heavy load on the starter motor, such that it fails to turn the engine. Damage (due to excessive compression and even dilution of the lubricating oil with fuel) can also occur. This condition is known as the engine "flooding out".
Some Mazda-made
Wankel engine
s are notable for occasionally flooding themselves when turned off before reaching normal operating temperatures. Worn fuel injectors can also cause flooding in rotary engines. When flooded, rotary engine
s become very difficult to start. To unflood a rotary engine, fuel flow must be cut while the engine is turned over by the starter in order to clear out excess fuel.
The conventional remedy on a carbureted engine is to steadily hold the throttle wide open (full throttle) while cranking (starting) the engine. This permits the maximum flow of air through the engine, flushing the excess fuel out the exhaust. On a fuel-injected engine, ignoring the throttle (no fuel) while starting permits electronic logic systems to choose the correct fuel mixture, often based on exhaust gases. In either case, 'pumping' the throttle will only make it worse as that pumps even more excess fuel into the engine.
In worst cases, the excess fuel can foul spark plug
s, sometimes necessitating their replacement before the engine will start. This is most likely to occur on a carbureted engine in cold weather, after the engine has been running, then shut off for about a half-hour. This tends to fool the (cooling) choke to set as though the (warm) engine is cold, creating a too-rich fuel mixture, thus flooding the engine.
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
that has been fed an excessively rich air-fuel mixture that cannot be ignited. This is caused by the mixture exceeding the upper explosive limit for the particular fuel. An engine in this condition will not start until the excessively rich mixture has been cleared. It is also possible for an engine to stall from a running state due to this condition.
Engine flooding was a common problem with carbureted cars, but newer fuel-injected ones are immune to the problem when operating within normal tolerances. Flooding usually occurs during starting, especially under cold conditions or because the accelerator has been pumped. It can also occur during hot starting; high temperatures may cause fuel in the carburetor float chamber to evaporate into the inlet manifold, causing the air/fuel mixture to exceed the upper explosive limit. High temperature fuel may also result in a vapor lock, which is unrelated to flooding but has a similar symptom.
A severe form of engine flooding occurs when excessive liquid fuel enters the combustion chamber. This reduces the dead volume of the combustion chamber and thus places a heavy load on the starter motor, such that it fails to turn the engine. Damage (due to excessive compression and even dilution of the lubricating oil with fuel) can also occur. This condition is known as the engine "flooding out".
Some Mazda-made
Mazda
is a Japanese automotive manufacturer based in Fuchū, Aki District, Hiroshima Prefecture, Japan.In 2007, Mazda produced almost 1.3 million vehicles for global sales...
Wankel engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...
s are notable for occasionally flooding themselves when turned off before reaching normal operating temperatures. Worn fuel injectors can also cause flooding in rotary engines. When flooded, rotary engine
Rotary engine
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...
s become very difficult to start. To unflood a rotary engine, fuel flow must be cut while the engine is turned over by the starter in order to clear out excess fuel.
The conventional remedy on a carbureted engine is to steadily hold the throttle wide open (full throttle) while cranking (starting) the engine. This permits the maximum flow of air through the engine, flushing the excess fuel out the exhaust. On a fuel-injected engine, ignoring the throttle (no fuel) while starting permits electronic logic systems to choose the correct fuel mixture, often based on exhaust gases. In either case, 'pumping' the throttle will only make it worse as that pumps even more excess fuel into the engine.
In worst cases, the excess fuel can foul spark plug
Spark plug
A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...
s, sometimes necessitating their replacement before the engine will start. This is most likely to occur on a carbureted engine in cold weather, after the engine has been running, then shut off for about a half-hour. This tends to fool the (cooling) choke to set as though the (warm) engine is cold, creating a too-rich fuel mixture, thus flooding the engine.