Open-Loop, Wow !!! Is it a loop in the space time continuum? No my dear Spock, it's not....



(for more information please refer to the Cranking Enrichment Mode blog)

• Open-loop mode – simply leans that the ECM is NOT looking at the O2 sensor for A/F feedback and is reached after the engine has warmed-up sufficiently. At this point in time, the ECM enters open-loop mode and sets the injector pulse at base duration. The base injection duration is the beginning of any fuel control strategy, regardless of vehicle manufacturer. In the next mode (closed-loop), the base injection pulse duration is further modified, by adaptive memory values stored in RAM/KAM and based on system sensor readings. Open-loop mode simply means that the O2 sensor is not determining the injection pulse-width and the A/F ratio is not stoichiometric. The ECM adjusts injector pulse-width from a look-up table according to RPM, MAF/MAP value, intake air temperature (to calculate density) and throttle position. A further sub-mode that is also considered by the ECM is EGR operation, since it will affect the intake vacuum and/or air density. As soon as the O2 sensor starts cycling (crossing the 450 mV mark), the ECM switches to closed-loop and the A/F ratio is maintained at stoichiometric ratio. In closed-loop, the ECM uses the O2 sensor as a feedback to maintain the A/F mixture at stoichiometry. The open-loop mode is also a good indication of an ECM stuck in LIMP-in-MODE (sub-mode). A warmed-up engine stuck in open-loop points to a faulty condition outside the ECM’s control that is affecting the A/F ratio. While in limp-in-mode, the fuel trims PIDs can not be used to aid in diagnostics. A lean/rich condition (plugged injectors or leaky intake gasket), therefore, would not be apparent by FUEL TRIM PID analysis. A condition such as a faulty transmission solenoid (causing it not to shift) may take the fuel system into limp-in-mode masking any other A/F related problems.

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ECM/PCM Modes Cranking Enrichment   Warm-up Cycle         Open-Loop            Closed-Loop            Accel. Enrichment Deceleration Leaning   Idle Control             Low-Voltage Correction Clear Flood Mode     Selective Inj. Cut-Off   Limp-In Mode           Exhaust Variable Valve

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