Valve fault detection

A method comprising:

• operating an engine having a plurality of cylinders in a skip fire mode;
• estimating an expected net torque during a selected operating window utilizing a torque model, wherein the torque model considers an expected torque contribution from each of the cylinders and accounts for the effects of specific skip fire firing decisions that affect the expected torque contribution from each cylinder during the selected operating window;
• directly or indirectly measuring a parameter indicative of actual engine torque during the selected operating window;
• determining whether an exhaust valve actuation fault has occurred that caused an unexpected high pressure exhaust spring to occur in a selected cylinder based at least in part on a comparison of the measured parameter to an expected parameter value that is based at least in part on the expected net torque, wherein the determination is made within one engine cycle of the occurrence of the valve actuation fault;
• and
• when it is determined that an unexpected high pressure exhaust spring has occurred, preventing an intake valve associated with the selected cylinder from opening into the unexpected high pressure exhaust spring.

A system for detecting the existence of a high pressure exhaust spring in an engine cylinder of an engine having at least one cylinder, the system comprising:

• a processor and a computer readable media having programmed instructions for execution on the processor;
• a torque calculation model arranged to calculate an expected torque, the torque calculation model being included in the programmed instructions;
• a crankshaft acceleration prediction model arranged to calculated an expected crankshaft acceleration based on the expected torque, the crankshaft acceleration prediction model being included in the programmed instructions;
• a crankshaft acceleration detection module arranged to measure actual crankshaft acceleration;
• and
• a high pressure exhaust spring detection module arranged to detect the occurrence of a high pressure exhaust spring based at least in part on a comparison of the actual crankshaft acceleration to the expected crankshaft acceleration, the high pressure exhaust spring detection module being included in the programmed instructions, wherein the high pressure exhaust spring detection module is arranged to detect the occurrence of the high pressure exhaust spring within one engine cycle of the initial occurrence of the high pressure exhaust spring.