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

AC-GND-DC

TIME/DIV.

10ms

VOLTS/DIV.

Other

Engine

Idling

MPI – TROUBLESHOOTING

13A-95

• 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

VOLTS/DIV.

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

Probe switch

x10

AC-GND-DC

VOLTS/DIV.

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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