Gm Global Technolgoy Operations, Inc.

Joseph M Kotzan

Gregory E Labus

Clifford R Carlson

Leo H Voelkle

A comprehensive air injection system diagnostic uses hardware already available on many vehicle exhaust systems to monitor the oxygen content of the exhaust, so as to indicate steady state oxygen levels therein that are not in accord with the present state of the air injection system, and accordingly are assumed to be the result of a failure in the air injection system.

Air injection system diagnostic

The fuel system of an internal combustion engine diagnosed based on a learn term adjusted in response to a closed loop adjustment of the air fuel ratio and which is used along with the closed loop adjustment to determine the fuel amount supplied to the engine. The learn term is adjusted at a first rate based on the integral correction term. If the learn term reaches a predetermined primary rich or lean limit value and the closed loop integral adjustment reaches its authority limit, the learn term is further adjusted at a second rate that is slower than the first rate. When the learn term exceeds a predetermined secondary rich or lean limit value representing an adjustment that is greater than the adjustment represented by the corresponding primary rich or lean limit value, a fuel system fault is indicated.

Vehicle engine fuel system diagnostics

Idle air control apparatus for a vehicle driving internal combustion engine having an air induction passage includes a control valve in the air induction passage controlled by a stepper motor in response to the arithmetic count of applied electrical pulses, a register effective to store a valve control number representing the currently desired position of the control valve, apparatus effective upon occurrence of a predetermined engine loading event to change the valve control number in response thereto, an up-down counter effective to arithmetically count the pulses applied to the stepper motor and thus indicate actual control valve position, a closed loop control effective to compare the contents of the up-down counter and register and apply pulses to the stepper motor at the first predetermined rate to reduce any difference therebetween and a speed trim loop active only during occurrence of a predetermined steady state idle condition to compare actual engine speed with the desired engine idle speed and arithmetically change the valve control number in the register at a second predetermined rate substantially slower than the first predetermined rate to reduce any difference between said speeds. Thus idle air control responds to large, sudden engine load changes and environmental factors to prevent engine stall but ignores small random speed fluctuations to maintain a stable engine idle.

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Clarkston, MI, United States of America

Joseph M Kotzan