The optimization of a high performance engine in order to achieve maximum power at full load and high speed can cause an unstable behavior when the engine is running at different conditions, thus making a robust combustion diagnosis for on board diagnostic EOBD/OBD II purposes (misfiring detection) particularly challenging. In fact, when a misfire occurs, its detection can be critical because of the high background noise due to high indicated mean effective pressure (IMEP) cyclic variability.
A partial reduction of the high IMEP variability had been achieved by optimizing control parameters of a new prototype high performance V8/4.2 l engine. Spark advance and VVT phasing maps had in fact been re-designed based on in-cylinder pressure variability (cycle by cycle and cylinder by cylinder) analysis.
In this paper the focus is the analysis of innovative misfire diagnosis techniques (such as joint time-frequency analysis of the engine speed signal) to make the new prototype V8 engine compliant with EOBD/OBD II regulations.
The instantaneous engine speed signal has been recorded during experimental tests while inducing various misfire patterns. Both test rig investigations (i.e., off-line data processing) and real time analysis for OBD purposes have been carried out.
The basic misfire detection algorithm has been modified by introducing a pre-processing of the experimental data, allowing to improve the effectiveness of the misfire detection also at higher engine speed operating conditions.