The development of more affordable sensors together with the enhancement of computation features in current Engine Management Systems (EMS), makes the in-cylinder pressure sensing a suitable methodology for the on-board engine control and diagnosis. Since the 1960’s the in-cylinder pressure signal was employed to investigate the combustion process of the internal combustion engines for research purposes. Currently, the sensors cost reduction in addition to the need to comply with the strict emissions legislation has promoted a large-scale diffusion on production engines equipment. The in-cylinder pressure signal offers the opportunity to estimate with high dynamic response almost all the variables of interest for an effective engine combustion control even in case of non-conventional combustion processes (e.g. PCCI, HCCI, LTC). Furthermore, the accuracy of feed-forward control methodologies along real-life operation is affected by engine aging and production tolerances as well as environmental and driving conditions. Consequently, the control adaption through the feedback based on the in-cylinder pressure allows overcoming these issues. In this paper the features of two methodologies based on the in-cylinder pressure signal for the estimation of the Air-Fuel ratio and the in-cylinder trapped mass have been exploited in transient and steady-state conditions, respectively. Suitable post-processing of in-cylinder data has been carried out to handle the time delay with the sensors measurement and improve the estimation accuracy along the identification process. The techniques have been experimentally tested at the engine test stand on a Common-Rail turbocharged Diesel engine. The results exhibit good accuracy and a computational burden suitable with current EMS features.