Abstract: A method of detecting low compression pressure by interpreting acceleration of an engine crankshaft (201) is detailed. In a preferred embodiment, the method teaches measurement of intake manifold pressure. Then, a first engine crankshaft acceleration is measured, preferably proximate a maximum rate of compression, for a cylinder (113), and a first variable (307) indicative of the first engine crankshaft acceleration is provided. Then, a second engine crankshaft acceleration is measured, preferably proximate the cylinder's top-dead-center position (105), and a second variable (311) indicative of the second engine crankshaft acceleration is provided. Then, the method combines (313) the intake manifold pressure, the first variable, and the second variable and provides a compression pressure variable as a function of the combined variables. Other embodiments include subsets of the above variables to provide a compression pressure variable as a function of the combined variables.

Abstract: A apparatus and method of detecting a leak in an evaporative emissions system measures vapor flow out of the evaporative emissions system while maintaining a zero pressure difference from inside a fuel tank to atmosphere and provides a reference vapor flow variable dependent on the measurement (317). A pressurized vapor and leak flow variable is measured (323) dependent on measured vapor flow out of the evaporative emissions system while maintaining a pressure difference of 10" of water from inside the fuel tank to atmosphere. A leak is indicated (327) if a difference between the reference vapor flow variable and the pressurized vapor and leak flow variable is greater than a predetermined leak flow factor.

Abstract: A system, and corresponding method, for detecting the presence of a misfire condition by interpreting spectral activity of a running engine includes a device (309, 313) for measuring a characteristic, preferably an acceleration characteristic indicative of the running engine's performance, A spectral discrimination device (319), preferably a digital filter, receives a composite signal (317) provided by the measuring device (309, 313). The digital filter (319) provides a normal firing signal (321), corresponding to spectral energy attributable to a portion of the composite signal (317) representative of a normal firing condition in the running engine, and a misfire signal (323), corresponding to spectral energy attributable to another portion of the composite signal (317) representative of a misfiring condition in the running engine. A comparison device (325) provides and indication of a misfire condition (327) when a magnitude of the misfire signal (323) exceeds a magnitude of the normal firing signal (321).