ABS ISUZU TROOPER 1995 Workshop Manual

6E2-1 04 DRIVEABILITV AND EMISSIONS
Engine Coolant Temperature (ECT) Sensor
A "Scan tool" displays engine temperature in degrees
centigrade. After engine is started, the temperature
should rise steadily to about 90°C then stabilize when
thermostat opens. If the engine has not been run for
several hours (overnight), the engine coolant
temperature (ECT) and intake air temperature (IAT)
readings should be close to each other. A fault in the
ECT sensor circuit should set a diagnostic trouble code
(DTC) 14. The DTC charts also contain a chart to check
for sensor resistance values relative to temperature.
Intake Air Temperature (IAT) Sensor
A "Scan tool" displays temperature of the air entering
the engine and
should read close to ambient air
temperature when engine
is cold, and rise as under
hood temperature increases.
If the engine has not
been run for several hours (overnight), the IAT sensor
temperature and
ECT readings should be close to each
other. A
failure in the IAT sensor circuit should set a
DTC 23. The DTC charts also contain a chart to check
for sensor resistance values relative to temperature.
Heated Oxygen Sensor (H02S)
The "Scan tool" has several positions that will indicate
the state
of the exhaust gases, Oxygen voltage,
integrator, and block learn. See "Scan tool" position
information in
"Introduction", "Driveability and
Emission," in this section.
A
problem in the oxygen sensor circuit, or fuel system,
should set a DTC 13 (open circuit), DTC 44 (lean
indication)/DTC 45 (rich indication). Refer to
applicable chart, if any of these DTC(s) were stored in
memory.
Throttle Position (TP) Sensor
A "Scan tool" displays throttle position in volts. On 3.2L
engine, Throttle position
(TP) sensor voltage should
read below 0.85 volts, with throttle closed and ignition
"ON", or at idle. Voltage should increase at a steady
rate
as throttle is moved toward wide open throttle.
The Engine
Control Module (ECM) has the ability to
auto-zero the TP sensor voltage if it is below about 0.85
volts. This means that any voltage less than 0.85 volts
will
be determined by the ECM to be 0% throttle.
Some
"Scan tools" have the ability to read the throttle
angle and should read 0%, when the throttle is closed.
A failure in the TP sensor or circuit should set a DTC 21.
Manifold Absolute Pressure (MAP) Sensor
"Scan tool" displays manifold pressure in volts. Low
pressure (high vacuum) reads a
low voltage, while a
high pressure
(low vacuum) reads a high voltage. A
failure in the Manifold Absolute Pressure (MAP) sensor
circuit
should set a DTC 33 and using the chart will find
the cause
of the problem. A DTC 33 may be set if a
rough or unstable
idle exists. CHART C-1 D can also be
used
to check MAP sensor.
Vehicle Speed Sensor (VSS)
A "Scan tool" reading should closely match with
speedometer reading with drive wheels turning. A
failure in the vehicle speed sensor circuit should set a
DTC 24.
AIR CONDITIONING (A/C) Request Signal
When air conditioning in "ON", the "Scan tool" should
indicate air conditioning "ON".
See
"Air Conditioning Compressor Clutch Control
System",
Section "6E2-C1 0" for A/C electrical system
diagnosis.
Power Steering Pressure (PSP) Switch
A "Scan tool" should read "OFF" normally, and "ON"
with high pressure. This reading may vary with
different "Scan tools". Refer to CHART C-1 E for power
steering pressure switch diagnosis.
Crankshaft Position (CKP) Reference Signal
The ignition control module sends a signal to the ECM,
which is used to calculate proper spark advance and
fuel delivery. A "Scan tool" will read this signal and is
displayed in revolution per minute.
See "Electronic
Ignition System",
Section "6E2-C-4" for more
information on the ignition system (ignition control).
Park/Neutral Position (PNP) Switch
A "Scan tool" should read park/neutral position when
in park, or neutral, and R-D, L, when in drive or
overdrive. This reading may vary with different makes
of tools. Refer to CHART C-1 A for park/neutral position
switch diagnosis.
Knock Sensor (KS)
A "Scan tool" will indicate when the knock sensor
module signals the ECM that knock is present. See
"Knock
Sensor System," Section "6E2-C5" for further
information on the knock sensor system.
ON-VEHICLE SERVICE
ENGINE CONTROL MODULE (ECM)
The ECM is programmed from the factory and has no replaceable calibration chip.
•

wcAUTION:
' • When replacing the production Engine Control
Module
(ECM) with a service ECM (controller),
it is important to transfer the broadcast
diagnostic
trouble code and production ECM
number to the service ECM label. Please do not
record on ECM cover. This will allow positive
identification
of ECM parts throughout the
service
life of the vehicle.
DRIVEABILITV AND EMISSIONS 6E2-1 05
\fCAUTION:
' • To prevent internal ECM damage, the ignition
must be
"OFF" when disconnecting or
reconnecting power
to ECM (for example;
battery cable, ECM pigtail, ECM fuse, jumper
cables etc.)
ENGINE CONTROL MODULE (ECM) REPLACEMENT
Removal steps 1. Negative battery cable 2. Lower trim panel at console
3. A/C Heater transfer tube ECM 4. ABS controller electrical
controller
5. ABS controller 6. Four fasteners for ECM bracket
7. ECM electrical connectors
8. ECM from under dash bracket still attached
Installation steps To install, follow the removal steps
reverse in the order.
Fig. 6E2-55
EJ REMOVAL
1. Negative battery cable
2. Lower trim panel at console (4 fasteners)
3. Air Conditioning Heater transfer tube
4. ABS controller electrical connector (1) (if
equipt)
5. ABS controller (4 fasteners) (if equipt)
6. Four (4) fasteners for ECM bracket
7. ECM
electrical connectors (2)
8. ECM from under dash, bracket
still attached
NOTE:
To prevent possible Electronic Discharge damage
to the ECM, Do not touch the connector pins or
soldered components on the circuit board.
I•+! INSTALLATION
1. ECM and bracket under dash
2. Four (4) fasteners and tighten
3. Two (2) ECM electrical connectors
4. ABS controller and four (4) fasteners (if equipt)
5. ABS controller electrical connector (if equipt)
6. Air Conditioning Heater transfer tube
7. Lower trim panel at console (4 fasteners)
8. Negative battery
cable
Functional
Check
1. Turn ignition "ON".
2. Enter diagnostics test mode.
A.
Allow Diagnostic Trouble Code (DTC) 12 to
flash four times to verify no other DTC(s) are
present. This indicates the reprogrammed
ECM is functioning properly.
B. If DTC 51 occurs, or if the malfunction
indicator lamp is "ON" constantly with no
DTC(s), the
ECM is defective.
• If it is necessary to replace the ECM, follow
the previous removal instructions.
ENGINE COOLANT TEMPERATURE (ECT)
SENSOR
Fig. 6E2-56

New or service sensors will already have the
compound
applied to the threads. If a sensor is
removed
from an engine and iffor any reason it
is to be reinstalled, the threads must have anti­
seize compound
applied before reinstallation.
•
Apply anti-seize compound or equivalent to
threads of oxygen sensor if necessary.
• Tighten the oxygen sensor to the specified
torque.
1~1 Torque N·m (lb·ft) 55 (40)
1. H02S wiring connector
THROTTLE POSITION (TP) SENSOR
Fig. 6E2-59
E) REMOVAL
Preparation: • Battery negative cable.
1. Throttle Position (TP) sensor wiring connector
2. TP sensor fixing screw
3. TP sensor
I••IINSTALLATION
3. TP sensor
2. TP sensor fixing screw
• Tighten the fixing screw to the specified torque.
~~~ Torque N·m (lb·in) I 2 (18)
• Use a "Scan tool" to check TP sensor output
voltage with throttle closed, should be under
0.85 volts. If over 0.85 volts, check for binding
throttle shaft, or TP sensor lever. If all OK,
replace TP sensor.
1.
TP sensor wiring connector
DRIVEABILITY AND EMISSIONS 6E2-1 07
MANIFOLD ABSOLUTE PRESSURE
(MAP) SENSOR
1. Vacuum hose
) 0~
2 .• ,.~,,~,~
conne~ JJJ
4. Sensor
Fig. 6E2-60
E) REMOVAL
Preparation: • Battery negative cable.
1. Vacuum hose
2. Electrical connector
3. Attaching screws
4. Sensor
I••IINSTALLATION
4. Sensor
3. Attaching screws
2. Electrical connector
1. Vacuum hose
VEHICLE SPEED SENSOR (VSS)
Refer to INSTRUMENT PANEL CLUSTER AND
CONSOLE of this manual for replacement of vehicle
speed sensor located in instrument panel.
POWER STEERING PRESSURE (PSP)
SWITCH
Refer to STEERING, SUSPENSION, TIRES AND
WHEELS for service of the power steering pressure
switch.
PARK/NEUTRAL
SWITCH POSITION
(PNP}
See
Section AUTOMATIC TRANSMISSION GENERAL
INFORMATION Section for park/neutral position
switch.
"On-Vehicle Service" and adjustment
procedures are
also listed there.

6E2-11 0 DRIVEABILITY AND EMISSIONS
CHART C-10
MANIFOLD ABSOLUTE PRESSURE (MAP) OUTPUT CHECK
Circuit Description:
Manifold Absolute Pressure (MAP) sensor measures the changes in the intake MAP which result
from engine load
(intake manifold vacuum) and revolution per minute changes; and converts these into a voltage output. The
Engine
Control Module (ECM) sends a 5-volt reference voltage to the MAP sensor. As the MAP changes, the
output voltage of the sensor also changes. By monitoring the sensor output voltage, the ECM knows the MAP. A
lower pressure (low voltage)
output voltage will be about 1 - 2 volts at idle. While higher pressure (high voltage)
output voltage
will be about 4-4.8 at Wide Open Throttle. The MAP sensor is also used, under certain conditions,
to measure barometric pressure,
allowing the ECM to make adjustment for different altitudes. The ECM uses the
MAP sensor
to control fuel delivery and ignition timing.
Test Description:
Numbers
below refer to circled numbers on the diagnostic chart.
\fl CAUTION
'(/ • Be sure to use the same Diagnostic Test Equipment for all measurements.
CD When comparing "Scan tool" readings to a known good vehicle, it is important to compare vehicle that use a
MAP sensor having the same color insert
or having the same "Hot Stamped" number. See figures on facing
page.
® Applying 34 kPa (1 0" hydragyrum) vacuum to the MAP sensor should cause the voltage to be 1.5-2.1 volts
than the voltage at
Step 1. Upon applying vacuum to the sensor, the change in voltage should be
instantaneous. A slow voltage change indicates a faulty sensor.
® Check vacuum hose to sensor for leaking or restriction. Be sure that no other vacuum devices are connected ....-...
the MAP hose. ~
NOTE:
Make sure electrical connector remains securely fastened.
@) Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connection. Output
changes greater that
.1 0 volt indicate a bad sensor.
MANIFOLD
ABSOLUTE PRESSURE
SENSOR
TO MANIFOLD
ABSOLUTE PRESSURE
(VACUUM)
HARNESS ENGINE
CONNECTOR
(BLUE) TOTPS
TOECT SENSOR
Fig. 6E2-62
GRY
ENGINE CONTROL
MODULE(ECM)
I---...JVV'--5 VOLT
REF
SENSOR -GROUND
•

DRIVEABILITV AND EMISSIONS 6E2-111
CHART C-10
MANIFOLD ABSOLUTE PRESSURE (MAP) VOLTAGE OUTPUT CHECK
CD • IGNITION UON" ENGINE "OFF"
• uSCAN TOOL" SHOULD INDICATE A MANIFOLD ABSOLUTE
PRESSURE (MAP) SENSOR VOLTAGE. • COMPARE THIS READING WITii!TH READING OF A KNOWN
GOOD VEHICLE. SEE FACING E TEST DESCRIPTION, STEP 1. • VOLTAGE READING SHOULD E THE SAME± 0.40 VOLT.
® • DISCONNECT VACUUM HOSE AT MAP SENSOR AND PLUG HOSE.
• CONNECT A HAND VACUUM PUMP TO MAP SENSOR.
• START ENGINE.
•
APPLY 34 kPa (10" HYDRAGYRUM) OF VACUUM AND NOTE VOLTAGE CHANGE.
VOLTAGE CHANGE SHOULD BE 1.5-2.1 VOLTS LESS THAN STEP 1. IS IT?
@ NO TROUBLE FOUND. CHECK SENSOR HOSE FOR LEAKAGE OR RESTRICTION. BE SURE THIS HOSE
SUPPLIES VACUUM TO MAP SENSOR ONLY.
~3
@ CHECK SENSOR CONNECTION. IF OK, REPLACE SENSOR
Hot-stamped number
CLEAR DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION
INDICATOR LAMP OPERATION.

MODES OF OPERATION
The Engine Control Module (ECM) uses voltage inputs
from several sensors to determine how much fuel to
give the engine. The fuel is delivered under one of
several conditions, called "modes". All the modes are
controlled by the ECM and are described below.
Starting Mode
When the ignition is first turned "ON", the ECM turns
"ON" the fuel pump relay for two seconds, and the fuel
pump builds up pressure. The ECM also checks the
Engine
Coolant Temperature (ECT) sensor and the
Throttle Position Sensor, and the determines the
proper
air/fuel ratio for starting. This ranges from 1.5:1
-36·c (-33.F) to 14.7:1, at 94•c (201.F) ECT.
The ECM controls the amount of fuel delivered in the
starting mode by changing
how long the injector is
turned
"ON" and "OFF". The is done by "Pulsing" the
injectors
for very short times.
Clear Flood Mode
If the engine floods, it may be cleared by pushing the
accelerator pedal down all the way. The ECM then will
fixed air/fuel ratio 16.5:1. The ECM holds this injector
rate
as long as the throttle stays wide open. If the
throttle position becomes less than approximately
70%, the ECM returns to the starting mode.
Run Mode
The run mode has two conditions called "Open Loop"
and "Closed Loop"
"Open Loop"
When the engine is first started, and it is above 500
Rovolution Per Minute (rpm), the system goes into
"Open Loop" operation. IN "Open Loop," the ECM
ignores the signal from the heated oxygen sensor
(H02S), and calculates the air/fuel ratio based on
inputs
from the ECT sensor and manifold absolute
pressure sensors.
The system stays in
"Open Loop" until the following
conditions are met:
1. The H02S has varying voltage output, showing
that
it is hot enough to operate properly. (This
depends on temperature.)
2. The ECT sensor is above a specified temperature.
3. A specific amount of time has elapsed after
starting the engine.
"Closed Loop"
The specific values for the above conditions vary with
different engines, and are stored in the ECM. When
these conditions are met, the system goes into
"Closed
Loop"
operation. In "Closed Loop", the ECM calculates
the air/fuel ratio (injector on-time) based on the signal
from the H02S. This allows the air/fuel ratio to stay
very close to 14.7:1.
DRIVEABILITV AND EMISSIONS 6E2-117
Acceleration Mode
The ECM responds to rapid changes in throttle position
and air
flow, and provides extra fuel.
Deceleration Mode
The ECM responds to changes in throttle position and
air
flow, and reduces the amount of fuel. When
deceleration is very fast, the ECM can cut off fuel
completely
for short periods.
Battery Positive Voltage Correction Mode
When battery positive voltage is low, the ECM can
compensate
for a weak spark delivered by the ignition
control module by:
• Increasing injector pulse width.
• Increasing the idle rpm.
• Increasing ignition dwell time.
Fuel Cutoff Mode
The fuel injectors are shut "OFF" if engine speed
"exceed" 6880 rpm (DOHC) or6800 rpm (SOHC). This is
to prevent damage to engine. When engine speed is
below 6880 rpm (DOHC) or 6800 rpm (SOHC), the fuel
injectors are again pulsed at a normal mode.

FUEL INJECTORS
The multipart fuel injection injector assembly is a
solenoid-operated device, controlled
by the Engine
Control Module (ECM), that meters pressurized fuel to
a single engine cylinder.
The
ECM energizes the low impedance (2.0 ohms) for
DOHC or High impedance (12.2 ohms) for SOHC
solenoid to a normally closed ball valve. This allows
fuel
to flow into the top of the injector, past the ball
valve, and through a recessed
flow director plate at the
injector outlet (Fig. 6E2-71). The director plate has six
machined holes
that control the fuel flow, generating a
conical spray pattern
of finely atomized fuel at the
injector tip. Fuel
from the tip is directed at the intake
valve, causing
it to become further atomized and
vaporized before entering the combustion chamber.
An injector which is stuck partially open
would cause a
loss
of pressure after engine shut down. Also, an
extended crank times would be noticed on some
engines. Dieseling could also
occ!Jr because some fuel
could be delivered
to the engine after the ignition is
turned
"OFF".
FUEL INJECTOR DRIVER OPERATION
The method of turning the Fuel Injectors "ON" and
"OFF" is called a "Peak" and "Hold" Driver System.
The
ECM uses a transistor to "Peak" Injector to open it.
A second set
of Injector Drivers will "Hold" the Injectors
open for the calculated pulse width. The ECM has three
(3) Injector Drivers, they are labeled A, 8, and C inside
the
ECM. Injector Driver "A" is used to open the Injector
initially (Peak) and depending on available battery
positive voltage
Injector Drive "8" or "C" is used to
"Hold" the Injector for the amount of time necessary to
inject the proper amount of fuel into the cylinder. A
resistor module in part
of the Injector Driver circuits to
protect the Injector Drivers from high current (amps). If
one of the Driver circuits become "Open" the vehicle
will
not start. Diagnosis of the Injector driver circuits
are done
with Chart A-3 "Cranks But Won't Run" chart
in
SECTION 6E2-A of this service manual.
FUEL PRESSURE CONTROL VALVE
ASSEMBLY
The fuel pressure control valve is a diaphragm­
operated relief valve
with fuel pump pressure on one
side and regulator spring pressure and intake manifold
absolute pressure on the other (Fig. 6E2-72).
The function
of the regulator is to maintain a constant
pressure differential across the injectors at all times.
The fuel pressure control valve compensates
for
engine load by increasing fuel pressure as engine
vacuum drops.
The fuel pressure control valve is mounted at the end
ofthe fuel rail, and is serviced as a complete assembly.
The system operates in
an acceptable pressure range
of 280 to 320 kPa (41 to 46 psi) with engine running.
If the pressure is too low, poor performance and a
DRIVEABILITV AND EMISSIONS 6E2-119
diagnostic trouble code 44 could result. If the pressure
is too high, excess odor and a diagnostic trouble code
45 could result.
CHART A-7 has information on diagnosing fuel
pressure conditions.
11. Fuel inlet
Fig. 6E2-71
1. Solenoid assembly
Spacer
and
guide assembly
. Ball valve
8. Cover-pressure regulator 1. Vacuum tube
7.
6.
Seal · 0-ring
Base assembly
Fuel
outlet fitting
Fig. 6E2-72

6E2-124 DRIVEABILITV AND EMISSIONS
E) REMOVAL
Preparation: • Engine hood
• Battery negative cable
1.
Air cleaner assy
2.
Accelerator pedal cable
•
Disconnect from throttle body and cable
brackets.
3. Canister vacuum hose
• Disconnect from vacuum switch valve (VSV).
4. Vacuum booster hose
• Disconnect from Common chamber duct.
5. Connectors
• Disconnect idle air control valve, throttle
position sensor, manifold absolute pressure,
canister
VSV, exhaust gas recirculation (EGR)
VSV, intake air temperature and VSV.
6. High tension cable
• Remove from cylinder heads.
7. Electronic ignition (EI) module assy
• Disconnect 3 connector from El module.
• Remove 3 bolts from El bracket and El assy.
8.
Throttle body (TB)
• Remove 4 bolts from TB.
9. Vacuum hoses
• Disconnect canister VSV and EGR VSV vacuum
hose
from TB.
10. Fuel pressure control valve vacuum hose
• Disconnect from common chamber duct.
11.
PCV hose
• Disconnect from common chamber duct.
12.
Evaporate emission canister purge hose
• Disconnect from common chamber duct.
13.
EGR valve assy
• Remove 4 bolts from common chamber duct
and exhaust manifold.
14.
Common chamber duct
• Remove 4 bolts, 4 nuts and 3 duct bracket fixing
bolts.
• Remove ground cable fixing bolt from rear of
common chamber duct.
15.
Common chamber
• Remove 6 bolts and 2 nuts.
• Remove common chamber bracket fixing bolts
from rear of common chamber.
16. Fuel
hose
• Feed and return hose from fuel pipe and 2 fixing
bolts
from cylinder head. 17.
Fuel
rail assembly
• Remove fuel injector connector.
• Remove fuel rail fixing bolts.
• Remove fuel rail assy.
j .. !•l DISASSEMBL V
NOTE:
• If
an injector becomes separated from the rail and
remains in the cylinder head, both injector
0-ring
seals and the retainer clip must be replaced.
1.
Regulator attaching screw
2. Fuel pressure control valve assembly
3. Injector retainer clip (Fig. 6E2-77)
4.
Multipart fuel injection injector assembly
5. Fuel rail
Fig. 6E2-77
l•! .. j REASSEMBL V
5. Fuel rail
4. Multipart fuel injection injector assembly
• Lubricate new injector 0-ring seal with engine
oil, and
install on injectors.
3.
Injector retainer clip
2. Fuel pressure control valve assembly
1. Regulator attaching screw
l·u·jiNSTALLATION
To install, follow the removal steps in the reverse
order.
THROTTLE BODY ASSEMBL V
The TB assembly repair procedures cover component
replacement
with the unit on the vehicle. However, TB
replacement requires that the complete unit be
removed from the engine.
The last three digits
of the eight digit identification
number are stamped on the
TB casting, next to the
throttle stop screw (Fig. 6E2-78). The part number
begins
with "17091 ... " Refer to this number if servicing
or part replacement is required.
•

6E2-134 DRIVEABILITV AND EMISSIONS
SECTION C-3
EVAPORATIVE EMISSION (EVAP) CONTROL SYSTEM
(ELECTRONICALL V CONTROLLED)
CONTENTS
General Description ...................... 6E2-134
Purpose ............................ 6E2-134
Vapor Canister ........................ 6E2-134
Evaporative Emission (EVAP) Control System .. 6E2-134 Results of Incorrect Operation ............. 6E2-135
Diagnosis ............................. 6E2-135
Visual Check of Canister ................. 6E2-135
On-Vehicle service . . . . . . . . . . . . . . . . . . . . . . 6E2-135
Fuel Vapor Canister . . . . . . . . . . . . . . . . . . . . 6E2-135
Canister Hoses . . . . . . . . . . . . . . . . . . . . . . . 6E2-135
Chart C-3 Evaporate Emission Canister
Purge Valve . . . . . . . . . . . . . . . . . . . . . . . . . 6E2-136
GENERAL DESCRIPTION
PURPOSE
The basic Evaporative Emission (EVAP) Control
System used on
all vehicles is the charcoal canister
storage method. This method transfers fuel
vapor
from the fuel tank to an activated carbon (charcoal)
storage device (canister)
to hold the vapors when the
vehicle
is not operating. When the engine is running,
the fuel
vapor is purged from the carbon element by
intake air flow and consumed in the normal
combustion process.
VAPOR CANISTER
Gasoline vapors from the fuel tank flow into the tube
labeled tank.
Any liquid fuel goes into a reservoir in the
bottom of the canister to protect the integrity of the
carbon bed above (Fig 6E2-86). These vapors are
absorbed into the carbon. The canister is purged
when
the engine is running or commanded by Engine
Control Module (ECM).
Ambient air is allowed into the
canister through the air tube in the top. The air mixes
with the vapor and the mixture is drawn into the intake
manifold.
EVAPORATIVE EMISSION (EVAP)
CONTROL SYSTEM
The solenoid used with this canister uses Vacuum
Switch Valve to control purge. The ECM opens and
closes the solenoid to control purge.
The
ECM operates a Normally Closed (N/C) solenoid
valve
which controls the vacuum to purge the charcoal
canister. Under cold engine
or idle conditions, the
solenoid is
not energized by the ECM, which blocks
vacuum
to purge the canister. The
ECM energizes
the solenoid valve and allows
purge when:
• Engine is warm above sg·c (156.F).
• After the engine has been running a specified
time.
4.
1. Vapor from Fuel Tank 4. Carbon
2. Evaporate Emission
Canister Purge
Vacuum
3. Canister Body
Fig. 6E2-86
3.
• Throttle position is above 7% throttle position
sensor.
•

6E2-138 DRIVEABILITY AND EMISSIONS
SECTION C4
ELECTRONIC IGNITION (EI) SYSTEM/IGNITION CONTROL (IC)
CONTENTS
General Description . . . . . . . . . . . . . . . . . . . . . 6E2-138
Purpose
............................ 6E2-138
Operation
........................... 6E2-138
Results of Incorrect Operation . . . . . . . . . . . 6E2-139
How diagnostic trouble code (DTC) 42 is
Determined ........................ 6E2-139
Diagnosis. . . . . . . . . . . . . . . ............. 6E2-139
Diagnostic
trouble code (DTC) 12 . . . . . . . . . 6E2-139
On-Vechicle Service . .

. . . . . . . . . . . . . . . . . . . 6E2-139
Electronic Ignition (EI) Assembly .......... 6E2-139
Crankshaft Position (CKP) Sensor ......... 6E2-140
Ignition Coil
.......................... 6E2-140
Ignition Control
Module (ICM) ............ 6E2-140
Ignition
Timing ....................... 6E2-140
Chart
C-4D-1 Electronic Ignition (EI) misfire
at
Idle .............................. 6E2-142
Chart C-4D-2 Electronic Ignition (EI) misfire
Under Load .......................... 6E2-144
GENERAL DESCRIPTION
PURPOSE
The Electronic Ignition (EI) system controls fuel
combustion by providing a spark to ignite the
compressed
air/fuel mixture at the correct time. To
provide improved engine performance,
fuel economy,
and
control of exhaust emissions, the Engine Control
Module
(ECM) controls spark advance timing with the
Ignition Control (IC) system.
OPERATION
The "EI" is a "waste spark" system in which 2 plugs are
fired
simultaneously from one coil. The spark plugs are
paired
to a coil, so that when both fire, one cylinder is
on the compression stroke and the other is on exhaust.
There is
Iitie resistance across the plug gap on the
exhaust stroke, so the
plug requires very little voltage
to fire, thereby providing the other plug (compression)
with maximum available voltage.
The system uses a magnetic Crankshaft Position (CKP)
sensor which protrudes into the block, within
approximately .050" of the crankshaft reluctor. The
reluctor is a special wheel cast on the crankshaft that
has seven machined
slots, six of which are equally
spaced 60° apart). The seventh slot is spaced 1 oo from
one
of the other slots. As the reluctor rotates with the
crankshaft, the
slots change the magnetic field of the
sensor, causing
an induced voltage pulse.
By counting the time between pulses, the Ignition
Control Module (ICM)
can recognize the pulse of the
seventh
slot (sync pulse). Based on this sync pulse, the
module sends the reference signal to the ECM to
calculate CKP (used to fire coils in correct sequence)
and engine speed.
To
properly control timing, the ECM relies on the
following information:
• Engine load (manifold absolute pressure or
vacuum).
• Atmospheric (barometric) pressure.
• Engine temperature.
• Intake air temperature.
• CKP
• Engine speed (revolution per minute).
The ignition
control system consisits of the "EI"
assembly (coils, module,
and CKP sensor), ECM and
connecting wires. These circuits
perform the following
functions:
• "EI" reference
The CKP sensor sends a signal to the ICM which
generates a reference
pulse which is sent to the
ECM. The ECM uses this signal to calculate CKP
and engine speed (also used to trigger the
injector).
• Reference ground (GND)
This wire is GNd through the module and makes
sure the GNd circuit has no
voltage drop between
the
ICM and the ECM, which if open, could affect
performance.
• Bypass
At about 400 revolution per minute, the ECM
applies 5 volts to this circuit to switch spark timing
control from the ICM to the ECM. An open or
grounded bypass circuit
will set a diagnostic
trouble code 42 and the engine will run at base
timing,
plus a small amount of advance built into
the
ICM.
• IGNITION CONTROL (IC)
The ECM uses this circuit (when bypass voltage is
applied) to trigger the "EI" module. The ECM uses
the
CKP to base its calculation of the amount of
spark advance needed under present engine
conditions.
•