Patent ID: 7594427

Claim:
An engine management system comprising: a rate based monitor operable to perform test cycles on a monitored system when predetermined conditions are met, a test cycle being completed when a correct operation or malfunction of the monitored system could have been detected irrespective of whether a malfunction or correct operation is detected, the rate based monitor comprising: a counter for counting a number of times a completed test cycle is performed; and a timer operable to define a test cycle completion timing, the timer timing a test cycle from a start of a test cycle until a timing when the correct operation or malfunction of the monitored system could have been detected irrespective of whether a malfunction or correct operation is detected, the timer being reset it one or more of the predetermined conditions cease to be met; wherein the counter is updated in response to the timer timing out on completion of a test cycle; the monitored system is a fuel system that includes a fuel tank, and the test cycle is operable to rest for a leak; and the rate based monitor is operable to effect a test cycle that includes: closing an air path shutoff valve in an air path from an air intake to the fuel system; opening a purge valve in a purge path from an engine intake manifold to the fuel system; closing the purge valve when a predetermined pressure is detected in the fuel system; and performing pressure computations based on measured pressures in the fuel system to detect a leak, a failure being notified in response to predetermined pressure computation results.