Feedback Mode; Advance Spark Speed Correction; Valve Timing Determination; Fuel Injection Control Outline [Lf] - Mazda 2006 MX-5 Service Highlights

Feedback Mode

Mode execution condition
• Except during cleaning, maximum cam retard, or feedback hold modes.
Purpose
• Feedback mode obtains valve timing suitable for engine operation conditions by performing the feedback
operation so that present OCV drive current is set closer to the target current determined by the PCM
according to engine operation conditions.
Operation
• Based on engine operation conditions, the target current is set between 100 mA (maximum retard) and 1,000
mA (maximum advance), using the neutral point of approx. 600 mA as a reference. Actually, the target current
is calculated by subtracting the current necessary for obtaining the target advance/retard amount, using a
reference at the hold-current learning value calculated from the neutral position of the spool valve.

Advance Spark Speed Correction

• If there is a large difference between the target valve timing and the actual valve timing, the target current
correction is applied so that it is set closer to the target valve timing more quickly to raise the advance spark
speed by advancing the spool valve initialization operation.
• The variable valve timing actuator advance spark speed increases as the hydraulic passage in the OCV widens
and decreases as it narrows.

Valve Timing Determination

• The PCM controls current to the OCV to obtain optimum valve timing suitable for the engine operation
conditions (target valve timing).
• The PCM compares target valve timing with actual valve timing, and feeds back the result to change valve
timing smoothly.
Target valve timing
• Determined according to engine speed and charging efficiency.
Actual valve timing
• Means present valve timing. Actual valve timing is calculated by adding the maximum cam retard learning value
for energization from the value detected by the CMP and CKP sensors.
Cam maximum retard learning value
• Though the intake camshaft valve timing (including maximum retard position) is detected based on the
difference between the signal from the sensor and signal from the CKP sensor, the difference between the
signals deviates due to the sensor installation condition. Because of this, the PCM stores the difference
between the signal build-ups at the maximum OCV retard position to prevent deviation in valve timing detection.
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FUEL INJECTION CONTROL OUTLINE [LF]

• Performs optimum fuel injection according to engine operation conditions.
• The PCM determines the engine operation conditions based on the signals from the following input devices and
drives the injectors at the optimum fuel injection time (fuel injection amount) and the fuel injection timing to
inject fuel. For the construction/operation of the fuel injector, refer to "FUEL SYSTEM, FUEL INJECTOR
CONSTRUCTION/OPERATION".
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CONTROL SYSTEM
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