FIRING ORDER:
FIRING ORDER: 1 5 3 6 2 1 5 3 6 2 44
The high speed (upper) Speed/Timing Sensor measures engine speed for normal operations including governing and crankshaft position for timing purposes and cylinder identification.
The cranking (lower) Speed/Timing Sensor is used during starting and allows continuous operation if the high speed sensor fails. A failure of the high speed sensor will cause the ECM to automatically switch to the cranking Speed/Timing Sensor. Also, the check engine lamp will turn ON.
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¥¥ TimiTiming mng marks (arks (arroarrow)w)
¥¥ TooTooth th arranarrangemengementt identifies TDC identifies TDC
¥¥ SensSensor or and and tootoothth arrangements prevent arrangements prevent reverse rotation reverse rotation
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The Timing Wheel is a part of the drive gear for the camshaft. Timing marks (arrow) are used to locate the wheel and the camshaft in the correct position relative to the crankshaft which is pinned at TDC. This Timing
Wheel is used in all 3406E engines with passive Speed/Timing sensors.
As previously stated, the Timing Wheel has a total of 25 teeth. One tooth is positioned midway between the adjacent teeth. This configuration is used by the ECM to locate TDC on the No. 1 cylinder (and subsequent cylinders).
INSTRUCTOR
INSTRUCTOR NOTE: NOTE: Reverse rotation prReverse rotation protection is accomplishedotection is accomplished by using the sequence in which the signals from the two sensors are by using the sequence in which the signals from the two sensors are received by the
received by the ECM. ECM. The spacing between the The spacing between the two sensors on two sensors on thethe wheel is 90
wheel is 90 degrees. degrees. If the interval between If the interval between the signals is 270 the signals is 270 degrees,degrees, this information is interpreted by
this information is interpreted by the ECM as the ECM as reverse rotation. reverse rotation. TheThe injectors will be disabled.
injectors will be disabled.
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¥¥ SpeeSpeed/tid/timing ming sensosensorsrs
¥¥ SensSensors ors genegenerate rate aa PWM signal from PWM signal from timing wheel teeth timing wheel teeth
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The Speed/Timing Sensors are positioned horizontally on the engine, but are positioned perpendicular to the timing wheel surface. In other words, they face the side of the the timing wheel, similarly to the 3408/3412E installation. However, the timing wheel is different as seen on the previous page.
The teeth and sensors generate a signal which is converted by the ECM to a Pulse Width Modulated (PWM) output signal for the purpose of timing and a frequency modulated output signal for speed measurement.
INSTRUCTOR NOTE:
INSTRUCTOR NOTE: A description of PWM A description of PWM signals is providedsignals is provided later in this presentation (Sensors and Systems).
later in this presentation (Sensors and Systems).
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¥¥ TimiTiming wng wheel heel teethteeth and spacing
SENSOR CRANKSHAFTCRANKSHAFT DEGREES
TIMING WHEEL ROTATION TIMING WHEEL ROTATION TIMING GEAR TOOTH TABLE
TIMING GEAR TOOTH TABLE TABLE
The Speed/Timing Sensors use the timing wheel with the teeth arranged as shown to determine:
- Top Dead Center No. 1 (When found, the cylinders can be identified.)
- Engine speed
The sequence of signals shown in the second column (duty cycle) is analyzed by the ECM. At this point, no fuel will be injected until certain conditions have been met.
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¥¥ AftAfter per pattatternern recognition recognition
¥¥ InitInitial firiial firing sequng sequenceence ABCDEF
SENSOR CRANKSHAFTCRANKSHAFTDEGREESDEGREES
15 15°
II 30
30°
TIMING WHEEL ROTATION TIMING WHEEL ROTATION TIMING GEAR TOOTH TABLE TIMING GEAR TOOTH TABLE TABLE
AFTER PATTERN
AFTER PATTERN RECOGNITIRECOGNITIONON
CYL NO. 5
FIRING ORDER ORDER 153624153624
CYL NO. 3 CYL NO. 3
TDC TDC
During start-up, the Cranking Speed Sensor initially monitors the pulses created by the passing teeth and identifies the sequence as shown. After a complete rotation, the control can recognize the location of TDC from the pattern in the above illustration.
During initial cranking, no fuel is injected until the following conditions are met:
The timing wheel has completed a full revolution.
TDC for all cylinders is identified by the control.
After the sensor has provided the necessary signals, the ECM is ready to start injection.
NOTE:
NOTE: The reference The reference points in the illustration are points in the illustration are positions on thepositions on the timing wheel where the control measures the point of injection and timing wheel where the control measures the point of injection and TDC.
TDC.
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¥¥ NormNormal oal operatperationion
¥¥ SigSignal panal pattetternrn identifies TDC
TIMING WHEEL ROTATION TIMING WHEEL ROTATION TIMING GEAR TOOTH TABLE TIMING GEAR TOOTH TABLE TABLE
ANGLE CYLINDERCYLINDER REFERENCE
REFERENCE NORMAL OPERATIONNORMAL OPERATION
CYL NO. 5
INJECTION ASSUMEDASSUMED TDC TDC
During normal operation, the ECM can determine timing from the sequence reference point for each cylinder. The reference point is stored by the ECM after calibration is performed.
Injection timing is calibrated by connecting a TDC probe to the service access connector on the engine harness, and by activating the calibration sequence with the Caterpillar ET service tool. The ECM raises the engine speed to 1100 rpm (to optimize measurement accuracy), compares the actual No. 1 TDC location to the assumed cylinder No. 1 TDC location, and saves the offset in the EEPROM (Electrically Erasable Programmable Read Only Memory).
NOTE:
NOTE: The calibThe calibration offration offset range iset range is limited ts limited to ±o ± 4 cranksh4 crankshaftaft degrees.
degrees. If the If the range is range is exceeded, the exceeded, the offset is offset is set to set to zero zero (no(no calibration) and a calibration diagnostic message is generated.
calibration) and a calibration diagnostic message is generated.
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¥¥ Unit Unit injeinjector ctor currecurrentnt flow
flow