Fuel intake, start and propagation of combustion were studied in a Z-liter in-line four-cylinder SI engine. Two-dimensional laser induced fluorescence was used to characterize the performance of the engine. A tunable excimer laser at 248 nm and a broadband excimer laser at 308 nm were used to measure simultaneously distributions of hydroxyl radicals and fuel. LIF measurements of fuel (iso-octane) were performed by adding diethyl-ketone as fluorescence tracer to the iso-octane. The complementary information obtained from fuel and hydroxyl radical distributions is shown and differences are pointed out. Cycle to cycle variations and averaged results are discussed as function of equivalence ratio.