Cherokee 4WD L6-242 4.0L VIN S MFI (1992)
Engine Control Module: Description and Operation
General Operation
OPERATION
As input signals to the SBEC change, the SBEC adjusts the responses sent to the output devices. For example, the SBEC must calculate a different
injector pulse width and ignition timing for idle than it does for Wide Open Throttle (WOT).
OPEN AND CLOSED LOOP MODES
There are seven modes of operation that determine how the SBEC responds to the various input signals. Modes of operation are separated into two
different types, OPEN LOOP and CLOSED LOOP.
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During OPEN LOOP modes the SBEC receives input signals and responds only to preset SBEC programming. Input from the oxygen (02)
sensor is not monitored during OPEN LOOP modes.
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During CLOSED LOOP modes the SBEC monitors the oxygen sensor input. This input indicates to the SBEC whether or not the calculated
injector pulse width results in the ideal air/fuel ratio of 14.7 parts of air to 1 part of fuel. By monitoring the exhaust oxygen content, using the
oxygen sensor, the SBEC can "fine tune" the injector pulse width to achieve optimum fuel economy and performance combined with low
emission levels.
MODES OF OPERATION
The Multi-Point Fuel Injection (MFI) system has the following modes of operation:
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Ignition switch ON
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Engine start-up (crank)
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Engine warm-up
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Idle
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Cruise
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Acceleration
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Deceleration
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Wide Open Throttle (WOT)
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Ignition switch OFF
The ignition switch on, engine start-up (crank), engine warm-up, acceleration, deceleration, wide open throttle, and ignition switch OFF modes are
OPEN LOOP modes. The idle and cruise modes, with the engine at operating temperature, are CLOSED LOOP modes.
