l-20
ENGINE <NON-TURBO>
-
Control System
The notches generate pulses from high to low in
the crankshaft position sensor output voltage. When
a metal portion of the counterweight aligns with
the crankshaft position sensor, the sensor output
voltage goes low (less than 0.3 volts). When a notch
aligns with the sensor, voltage spikes high (5.0 volts).
As a group of notches pass under the sensor, the
output voltage switches from low (metal) to high
(notch) then back to low.
If available, an oscilloscope can display the square
wave patterns of each voltage pulse. From the width
of the output voltage pulses, the PCM calculates
engine speed. The width of the pulses represent
the amount of time the output voltage stays high
before switching back to low. The period of time
the sensor output voltage stays high before switch-
ing back to low is referred to as pulse width. The
faster the engine is operating, the smaller the pulse
width on the oscilloscope.
lates crankshaft angle (position). In each group of
timing reference notches, the first notch represents
69 degrees before top dead center (BTDC). The
second notch represents 49 degrees BTDC. The
third notch represents 29 degrees. The last notch
in each set represents 9 degrees before top dead
center (TDC).
The timing reference notches are machined to a
uniform width representing 13.6 degrees of crank-
shaft rotation. From the voltage pulse width the PCM
tells the difference between the timing reference
notches and the 60 degree signature notch. The
60 degree signature notch produces a longer pulse
width than the smaller timing reference notches.
If the camshaft position sensor input switches from
high to low when the 60 degree signature notch
passes under the crankshaft position sensor, the
PCM knows cylinder number one is the next cylinder
at TDC.
By counting the pulses and referencing the pulse
from the 60 degree signature notch, the PMC
calcu-
210”
I
150”
piiq
210”
1
I
TDC TDC
TDC
TDC
69”
49”29”
9”l
3
Crank
signal
+
+
I
Crank
360
400 440
480
520
560
600
640
600 720
angle
0
0
40 80
120
160
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240 280 320
0
40 80
120 160
200
240 280
320
0
AFU0072
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