A method for monitoring combustion processes of a cylinder of a spark ignited internal combustion engine, comprising the steps of: Retrieving a plurality of ion current signals from a combustion phase from a number of spark plugs (4A, 4B) of the cylinders to be monitored; Performing a first calculation on said ion current signals in a first calculation unit; Sending the result of the first calculation to a second calculation unit, and Comparing the results from the first calculation unit in the second calculation unit with corresponding results made on ion current signals from an engine running in a balanced mode, the results of said plurality of ion current signals being used in combination with each other in said second calculation unit, wherein the method further comprises the steps of: Dividing the ion current signals from a combustion phase into crank angle subintervals Calculating the integral of each ion current in each crank angle subinterval; and Performing a calculation by dividing the integral of ion currents from different subintervals such that the result of the calculation is dimension free; and characterised by Using the dimension free result for computing a statistical measure regarding deviation from the balanced mode that include second order or higher statistical moments such as statistical hypothesis tests or using Mahalanobi distance calculations. Retrieving a plurality of ion current signals from a combustion phase from a number of spark plugs (4A, 4B) of the cylinders to be monitored; Performing a first calculation on said ion current signals in a first calculation unit; Sending the result of the first calculation to a second calculation unit, and Comparing the results from the first calculation unit in the second calculation unit with corresponding results made on ion current signals from an engine running in a balanced mode, the results of said plurality of ion current signals being used in combination with each other in said second calculation unit, wherein the method further comprises the steps of: Dividing the ion current signals from a combustion phase into crank angle subintervals Calculating the integral of each ion current in each crank angle subinterval; and Performing a calculation by dividing the integral of ion currents from different subintervals such that the result of the calculation is dimension free; and characterised by Using the dimension free result for computing a statistical measure regarding deviation from the balanced mode that include second order or higher statistical moments such as statistical hypothesis tests or using Mahalanobi distance calculations. Dividing the ion current signals from a combustion phase into crank angle subintervals Calculating the integral of each ion current in each crank angle subinterval; and Performing a calculation by dividing the integral of ion currents from different subintervals such that the result of the calculation is dimension free; and characterised by Using the dimension free result for computing a statistical measure regarding deviation from the balanced mode that include second order or higher statistical moments such as statistical hypothesis tests or using Mahalanobi distance calculations.