Theory Of Operation

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The Powertrain Control Module (PCM) monitors the Injector timing controls and the time it takes for them to enter closed loop by using Zero Fuel Calibration (ZFC) . Zero Fuel Calibration (ZFC) is an algorithm used to detect deviations in individual injector's performance from their nominal behavior. There are two separate timers to monitor ZFC, a short-term timer and a long-term timer as described below.

Zero Fuel Calibration (ZFC) is an algorithm used to detect deviations in individual injector's performance from their nominal behavior. In an overrun/deceleration fuel shut-off condition, fuel rail pressure is set to a fixed value and small fuel injections are made on the respective injectors. The observed acceleration in crankshaft speed is detected and compared to the expected acceleration. If the observed acceleration deviates from the expected acceleration by a calibrated value, then an additional routine is called which adjusts the injection energizing time until the observed acceleration matches the expected value. This information is then used to adjust all pilot injections on that injector to ensure correct fuel delivery.

Short Term Timer - When the monitor of excessive time to enter closed loop fuel timing control with short term timer is enabled, a respective timer starts to increment. The timer stops when the ZFC learning values have been updated and an overrun has been detected. When this timer value is greater than a calibrated threshold and the closed loop ZFC has not been active within this calibrated amount of time based on the short term timer, the fault of "Excessive time to enter closed loop fuel timing control" will be set. The short-term timer measures the length of time it takes to enter closed loop compared to the ZFC diagnostic last run. The short term timer runs under more stringent conditions when it is likely that the closed loop ZFC will be active.

Long Term Timer - When the monitor of excessive time to enter closed loop fuel timing control with long term timer is enabled, a respective timer starts to increment. The timer stops when the ZFC learning values have been updated and an overrun has been detected. When this timer value is greater than a calibrated threshold and the closed loop ZFC has not been active within this calibrated amount of time based on the long term timer, the fault of "Excessive time to enter closed loop fuel timing control" will be set. The long-term timer runs any time it is possible for the closed loop ZFC, to be active.