An engine bench test has been developed to measure the total amount of liquid fuel wetting the intake walls of a S.I. port fuel injected engine under steady-state conditions.A four cylinder engine equipped with a double injection system was been utilized. One injection system was fed with 2-methyl-2-butene, which did not produce liquid fuel deposit on the intake manifold, the other injection system was fed with different types of fuel and both systems were set at the stoichiometric air-fuel ratio.Putting the injection commutation on, the 2-methyl-2-butene is suddenly replaced by the fuel of the second injection system. An oxygen sensor (UEGO type) monitors the air-fuel ratio excursion due to the injection commutation and the test runs until the A/F re-establishment at the stoichiometric level. The inlet air flow measurement and air-fuel ratio obtained by the UEGO sensor allow us to calculate the proportion of fuel that goes into the cylinder and the proportion of fuel forming the liquid fuel deposit on the intake manifold walls.The test has been used to evaluate the propensity of fuels to form a liquid deposition on the wall of the intake manifold.Cycle- to- cycle combustion variation (CoV Pmax) due to mixture inhomogeneity has been measured and considered as regards the amount of the intake wall wetting.