In this paper a combustion diagnostic method is presented where measured pressure data is used to calculate the heat release, local temperatures and concentrations of NO and other species. This is done by a multizone model where the lambda value, i.e. 1/equivalence ratio, in each zone can be chosen arbitrarily. In homogenous charge engines lambda is given by the global air/fuel ratio. The local lambdas during initial combustion in stratified charge and diesel engines have to be estimated either as an average value or with a chosen distribution.One new zone of each local lambda is generated and the temperature, volume and species in all old zones are updated at each time step of calculation. In this paper the model is demonstrated by using pressure data from pre-mixed and direct injected stratified charge natural gas SI engines and from a DI diesel engine.The pre-mixed data is used to validate the model as such while the ambition in the stratified charge and diesel cases has been to find the average local lambda that gives the same NOx emission as measured. The emphasis in the latter cases has been to study the influence on average local lambda of the duration of the fuel injection. Early injected fuel seems to burn at slightly leaner mixtures than later injected.