If the combustion chamber is flooded repeatedly with fuel then remains of fuel is left over after combustion. The remaining fuel sticks to the cylinder walls and dilutes the lubrication provided by the engine oil. The increased friction increases wear on the piston, piston rings and cylinder walls which ultimately results in increased oil consumption.
Possible causes for fuel flooding on Petrol engines:
Mixture too rich*
Incorrect ignition timing
Faults in the ignition system
* When ECUs are reprogrammed due to engine upgrades, tuners will often try to increase power beyond the reasonable parameters of the engine components. As a result these components will produce more heat. To combat this,b tuners will richen the mixture as this increases cooling. If the mixture is too rich, the wear is too high on the components and they will fail prematurely leading to increased oil consumption.
Possible causes for fuel flooding on Diesel engines: