Mitsubishi Lancer Evolution 8. Manual — part 177
MPI – TROUBLESHOOTING
13A-94
<Standard waveform>
Observation Conditions
Standard waveform
<Explanation of waveforms>
• Camshaft position sensors detect the compression top dead centre (TDC) for each cylinder. Simultaneous observation of this
and other control signals makes it possible to distinguish between each of the cylinders.
• Crank angle sensors are sensors designed to detect cylinder crank angles. For each 2 revolutions of the engine, 4 evenly
spaced crank angle sensor HIGH signals are output. So, by measuring the cycle time (seconds), the engine speed can be
calculated using the following formula:
Engine speed = 2/4T (seconds) x 60 = 30/T (seconds)
<Waveform Observation Points>
• Check that, as the engine speed increases, cycle time T gets shorter, and frequency increases.
2 engine revolutions (1 camshaft revolution)
Crank angle
sensor output
waveform
Camshaft
position
sensor output
waveform
Camshaft position sensor
Crank angle sensor
Probe switch
x1
x1
AC-GND-DC
DC
DC
TIME/DIV.
10ms
10ms
VOLTS/DIV.
2V
2V
Other
-
-
Engine
Idling
MPI – TROUBLESHOOTING
13A-95
<Examples of abnormal waveforms>
• Example 1
Waveform characteristics
Rectangular waveform is output, even when the engine is not started.
Cause of problem
Sensor interface fault
• Example 2
Waveform characteristics
Waveform is displaced to the left or right
Cause of problem
Loose timing belt
Sensor disk abnormality
9-3 Injectors
<Measurement Method>
(1) Undo injector connector, then connect the special test harness
(MB991348). (All terminals should be connected)
(2) Connect oscilloscope probe to injector connector terminal No.2.
Note
When doing engine ECU connector measurement, take measurements,
connecting oscilloscope probe, at each of the following terminals.
When looking at No.1 cylinder: Terminal No.1.
When looking at No.2 cylinder: Terminal No. 9.
When looking at No.3 cylinder: Terminal No. 24.
When looking at No.4 cylinder: Terminal No. 2.
<Standard waveforms>
Observation conditions
Oscilloscope
Standard waveform
Point A
Point B
injector drive
duration
Solenoid counter-
electromotive force
(about 7 x 10V)
Power supply
Voltage
Probe switch
x10
AC-GND-DC
DC
VOLTS/DIV.
1V
TIME/DIV.
0.5ms
Other
-
Engine speed
Idling
MPI – TROUBLESHOOTING
13A-96
Explanation of waveforms
• A power supply voltage is normally applied, but when there is a signal from the engine ECU, the voltage drops to about 0V
for the duration of that drive signal.
• When the signal from the engine ECU is cut, a voltage peak is seen as a result of the counter-electromotive force, then a
return to power supply voltage.
• Injector drive time:
Fuel injection time is determined by the engine ECU based on AFS and other sensor output values.
Injector drive time = effective injection time + ineffective injection time (ineffective drive time: for correcting operating delays
that result from drop in power supply voltage)
• Solenoid coil counter-electromotive force:
If the signal from the engine ECU is switched OFF, a counter-electromotive force occurs in the injector coil.
(about 65 to 75V)
• Power supply voltage:
When there is no signal from the engine ECU, power supply voltage will be applied. When this power supply voltage is low,
the ineffective injection time increases, and the drive time increases as well.
Waveform observation points
• Point A: Height of the solenoid coil counter-electromotive force
Point B: Injector drive time
10-4 ISC Servo (stepper motor)
<Measurement Method>
(1) Undo the ISC servo connector, then connect the special test harness
(MB991709). (All terminals should be connected)
(2) Connect the probe for each oscilloscope channel either to ISC servo
connector terminals Nos.1 and 3, or to terminals Nos.4 and 6.
Note
When doing engine ECU connector measurement, take
measurements for the following terminals.
Connect the probe for each oscilloscope channel either to terminals
Nos.14 and 28, or to terminals Nos.15 and 29.
Idling time
Racing time
Oscilloscope
Solenoid coil counter-electromotive force is low or does not exist
Injector solenoid shorts
Drive time
Synchronized with the MUT-II/III display
Harsh racing
The drive time is extended greatly for an instant,
then immediately matches engine speed
MPI – TROUBLESHOOTING
13A-97
Standard waveform
Observation conditions (2CH both the same)
Standard waveform
<Explanation of waveform>
• When, for example, ignition switches ON (and where engine cooling water temperature is 20ºC or less), or when A/C
operates, the waveform is seen for an instant.
• Motor coil counter-electromotive force:
When signal from engine ECU is switched OFF, a counter-electromotive force (about 30V) is seen in the motor coil.
• Induced electromotive force caused by motor turning:
Induced electromotive force, caused by motor turning, is seen.
<Waveform Observation Points>
• Check that standard waveform appears when motor operating conditions are met.
• Point A: Presence or absence of induced electromotive force from the engine turning (ref. Abnormal waveform Example 1.)
• Point B: Height of coil counter-electromotive force
Point B
Coil counter-
electromotive
force
(about 3 x 10V)
Point A
Induced electromotive
force caused by motor
turning
Motor coil powered duration
Stepper motor
control signal
waveform
Stepper motor
control signal
waveform
Probe switch
x10
AC-GND-DC
DC
VOLTS/DIV.
1V
TIME/DIV.
20ms
Other
Either ignition switch ON, OFF (engine cooling water temp.
20°C or less), or A/C switch ON, OFF (when idling)
Engine speed
-
Differences to standard waveform
Possible causes
Induced electromotive force is either absent or extremely low
Motor malfunction
Differences to standard waveform
Possible causes
Coil counter-electromotive force is either absent or extremely low Coil short
6AFO142
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