US Patent 10100770 Systems and methods for on-board cylinder leakdown testing

Methods and systems are provided for performing an onboard cylinder leakdown test in response to an indication of cylinder misfire. In one example, following an engine-off event and an engine temperature above a threshold, fuel is injected into the indicated cylinder under conditions wherein the cylinder is expected to be sealed, and the detection of hydrocarbon migration out of the cylinder indicates cylinder degradation. In this way, cylinder degradation may be accurately diagnosed without intrusive, time consuming, and difficult off-board cylinder leakdown tests.