1987 SUZUKI GRAND VITARA Service Repair Manual

COMPUTER CONTROLLED EMISSION CONTROL SYSTEM
[Feed back system]
A prime purpose of this system is to maintain a controlled air fuel ratio, allowing the catalyst to reduce
oxides of nitrogen, hydrocarbons, carbon monoxide and to improve fuel economy simultaneously.
The electronic control module (ECM) and the oxygen sensor are provided in this system.
The oxygen sensor mounted on the exhaust manifold monitors the exhaust gas air fuel ratio and signals to
the ECM.
The ECM processes the oxygen sensor signal and controls carburetor air fuel ratio by the operation of the
mixture control solenoid in the carburetor.
Thus the signal of the exhaust gas air fuel ratio sensed by the oxygen sensor is fed back to ECM and the
carburetor air fuel ratio is controlled.
[Electronic control module (ECM)]
The ECM controls the fuel cut system, idle-up system, bowl vent system, EGR system and secondary
throttle valve system, as well as the feed back system. The ECM is located under the glove box of the
instrument main panel. Refer to Fig. 5-l -9.
I1
* Engine coolant
temperature
* Engine speed
-Electronic
controlmodule
I I
* Throttle positiont(Micro Switches)
I I I\-
* Fuel cut solenoid valve
-44
* Engine room
- * Vent solenoid valvetempe.rature
* Idle-up actuator (TWSV)* Electric load
* Secondary throttle valve (VSV) , _ ~
r* Mixture control
solenoid valve
* Barometric
pressure
+ ECM supply
voltage
* Gear position
Fig. 5-l-8Computer con trolled emissioncon trot s ys tern
5- 10

Fig. 5- l-9 ECM
1. ECM
2. Instrument panel.
The ECM sensed parameters are as follows:
l Exhaust Oxygen Concentration.
It is sensed by the oxygen sensor installed on
the exhaust manifold.
1. Oxygen sensor
Fig. 5- I - 7 0Oxygen sensor2. Exhaust manifold
l Engine coolant temperature.
It is sensed by the thermal switch installed on
the intake manifold.
1. Thermal switch
2. Intake manifold
Fig, 5- I- 17Thermal switch
l Throttle position.
It is sensed by the micro switches (wide open
switch and idle switch) installed on the
carburetor.
1. Idle micro switch
2. Wide open micro switch
Fig. 5- 1-12 Micro switches
l Engine speed.
It is computed by the ECM based on the
electrical signal received from the ignition
system.
l Electric load.
The ECM senses electric loads of the follow-
ing items to provide idle speed compensation.
a. Small, tail, side marker, license light.
b. Rear defogger (if equipped).
c. Heater fan.
5-11

Gear position.
It is sensed by the fifth switch located on the
transmission. The switch turns “ON” when
the gear shift lever is shifted to fifth gear
position and “OFF” when shifted to positions
other than fifth gear position.
1. Fifth swirch
2. Transmission
Fig. 5-l-13 Fifth switch
l Altitude compensation.
When the vehicle is at high altitude and the
feed back system does not function, the air/
fuel mixture becomes richer because of low
air density. To compensate the richer air/
fuel mixture at high altitude, the high altitude
compensator is “ON” by sensing the baro-
metric pressure and sends a signal to the ECM.
Following the signal, the ECM controls the
mixture control solenoid in the carburetor,
thus compensating the air/fuel mixture.
1. High altitude compensator2. Thermal engine room switch
Fig. 5- I- 14 High altitude compensator and
thermal engine room switch
l Engine room temperature compensation.
Sensing the air temperature in the engine
room the thermal engine room switch sends
an electric signal to ECM to compensate the
air/fuel ratio of the mixture. When the air
temperature in the engine room is low, the
switch operates to make the mixture rich.
When the air temperature in the engine room
is high, the switch stops operating, which
means, the air/fuel ratio of the mixture is not
controlled by the switch. Refer to Fig. 5-1-l 4
for the thermal engine room switch.
[Three-way catalyst]
The three-way catalyst is provided in the exhaust
system (exhaust center pipe). The function of
the catalyst is to reduce the emission of CO, HC
and NOx in the exhaust gas by oxidizing or
converting them into CO2, Hz 0 and Nz respec-
tively.
BOWL VENTILATION SYSTEM
This system has a switch vent solenoid which is
operated by the ignition switch and the ECM. It
prevents the fuel vapor in the float chamber
from flowing out into the atmosphere both
when the engine is at a stop and at work. When
the ignition switch is at “OFF” position or when
cranking the engine (engine not started), the
vent passage is closed by the solenoid valve, and
therefore, the vapor flows from the float cham-
ber into the vapor storage canister. When the
engine is operating, the solenoid receives an
electrical signal from the ECM and its valve
keeps the inner vent passage open. As a result,
the vapor passes through the passage into the
carburetor and is drawn into the engine.
1. Switch vent solenoid
2. inner vent passage3. Solenoid valve
4. To canister
5. Float
Fig. 5-l-15 Bowl ventilation system
5-12

FUEL CUT SYSTEM
As shown in the figure, the fuel cut solenoid valve is provided in the primary slow system of the carbure-
tor to open and close the fuel passage of the slow system.
As turning the ignition switch “OFF” cuts off the electric current to the solenoid, the solenoid closes the
fuel passage. Thus this system contributes to preventing dieseling of the engine after the ignition switch is
turned “OFF”. Also, during the deceleration and provided that all below listed three conditions exist, the
fuel cut solenoid valve operates to cut the fuel feed to the engine temporarily by closing the fuel passage
when it received a signal from the ECM.
Such operation of this system prevents the three-way catalyst from getting heated high and improves fuel
economy.
Three conditions:
l The coolant temperature is normal.
l The idle micro switch is in “ON” position. In other words, the primary throttle valve is closed.
l The engine revolution is more than 2,400 rpm..
1. Fuel cut solenoid
2.ignition switch
3.Fuel passage
4. Idle micro switch
5.ECM
6.Ignition coil
7.Thermal switch
valve
-. .t/g. cut system
5-13

EXHAUST GAS RECIRCULATION (EGR) SYSTEM
This system controls the formation of NOx emission by recirculating the exhaust gas into the combustion
chamber through the intake manifold.
The diaphragm mounted in the EGR modulator is operated by back pressure of the exhaust gas to open
and close the valve. By this opening and closing action of the valve, the EGR modulator controls the
vacuum transmitted to the EGR valve.
Under a low load condition such as low speed driving, the exhaust pressure is low. In this state, the dia-
phragm in the EGR modulator is pushed down by the spring force and the modulator valve opens to allow
the air into the vacuum passage from the outside.
As a result, the vacuum transmitted to the EGR valve becomes smaller and so does the opening of the
EGR valve. Thus, less amount of exhaust gas is recirculated to the intake manifold.
Under a high load condition such as high speed driving, on the other hand, the exhaust pressure is high. By
the high exhaust pressure, the diaphragm in the modulator is pushed up and closes its valve. As the air
does not enter the vacuum passage in this state, the vacuum transmitted to the EGR valve grows larger
and so does the opening of the EGR valve. Thus, larger amount of exhaust gas is recirculated to the intake
manifold.
Under any one of the following conditions, the vacuum passage is closed by the TWSV or BVSV and the
vacuum is not transmitted to the EGR valve which, therefore, doesn’t operate.
l When the coolant temperature is low. (BVSV is closed)
l When the gear shift lever is shifted to fifth gear position and fifth switch is turned on. (TWSV is closed)
l When HAC is turned on. (TWSV is closed)
Other than the above, EG R valve opens and closes in accordance with the EG R modulator operation.
8
c,1.EGR modulator102.EGR valve
3.8VSV
J4.intake manifold5.Diaphragm
6.Valve7.Filter
8.HAC
9.Fifth switch
10.ECM
e Fresh air- Vacuum11. Battery
@!B Exhaust gas*---Air12. TWSV
Fig. 5-l- 17 EGR system operation
5-14

5-2. DIAGNOSIS
POSSIBLE CAUSES OF EMISSIONS TEST FAILURES
Excessive Emission
Hydrocarbons (HC)
ExplanationPossible Causes
Excessive hydrocarbons arel Engine not at normal operating temperature
caused by an air/fuel mixture
that is not burning completely.l Disconnected, obstructed, leaking, or misrouted
vacuum hoses
l Vacuum leaks
.
l Maladjusted idle mixture
l Improper adjusted/sticking choke
l Maladjusted initial spark timing
oDefective spark plugs, wires or distributor cap
l Malfunctioning MCV
lLead contamination of catalytic converter
l Malfunctioning feed back system
Carbon monoxide (CO)Excessive carbon monoxidel Engine not at normal operating temperature
emissions are due to a mixture
that is rich.0 Maladjusted idle mixture
l Improperly adjusted/sticking choke
l Lead contamination of catalytic converter
lLeaking carburetor fuel passages or gaskets
0 Carburetor float level
0 Restricted air cleaner element
l Malfunctioning feed back system
Oxides of nitrogen (Nox)Excessive oxides of nitrogen
are generally due to high tem-
peratures in the combustion
chamber.
l Obstructed/Ieaking/misrouted vacuum lines
0 Improper operation of the EGR system
l Plugged EGR passages
l Inoperative BVSV or TWSV
l Lead contamination of catalytic converter
l Malfunctioning feed back system
5-15

EGR DIAGNOSIS
Condition
Engine idles abnormally rough
and/or stalls.
Possible CauseCorrection
EGR valve vacuum hoses mis-Check EGR valve vacuum hose routing.
routed.Correct as required.
Leaking EGR valve.Check EGR valve for correct operation.
EGR valve gasket failed or looseCheck EGR attaching bolts for tightness.
EG R attaching bolts.If no loose, remove EGR valve and inspect
gasket.
Improper vacuum to EGR valveCheck vacuum from carburetor EGR port with
at idle.engine at stabilized operating temperature and
at idle speed.
Engine runs rough on light
throttle acceleration and has
poor part load performance.
Sticky EGR valve
EGR valve vacuum hose mis-
routed.
Loose EGR attaching bolts
Sticky or binding EGR valve.
Check EGR valve for correct operation,
Check EGR valve vacuum hose routing.
Correct as required.
Torque bolts.
Same as listing in “Engine idles Abnomrally
Rough and/or Stalls” condition.
Clean EGR passage deposits.
Perform EGR System Check.
EGR modulator valve blocked
or air flow restricted.
Check EGR modulator valve operation.
Engine stalls on decelerations.
Wrong or no EGR gasket.
EGR modulator valve blocked
of air flow restricted.
Install new gasket, torque attaching parts.
Check EGR modulator valve operation.
Restriction in EGR vacuum line.Check EGR vacuum lines for kinks, bends, etc.
Remove or replace hoses as required.
VSV filter plugged.
Sticking or binding EGR valve.
Check VSV for correct operation.
Check EGR valve for excessive deposits causing
sticky or binding operation.
Part throttle engine detonation.EGR modulator valve blockedCheck internal control valve operation.
of air flow restricted.
NOTE:
Non-functioning EGR valveInsufficient exhaust gas recircu-Check EGR valve hose routing. Check EGR
could contribute to partlation flow during part throttlevalve operation. Repair or replace as required.
throttle detonation. Detonationaccelerations.Replace valve as required. Check EGR passages
can be caused by several otherand valve for excessive deposit.
engine variables. Perform igni-Clean as required. Check VSV operation.
tion and carburetor related
diagnosis.
5-16

Condition
Engine starts but immediately
stalls when cold.
NOTE:
Stalls after start can also be
caused by carburetor problems.
PCV SYSTEM DIAGNOSIS
Condition
Unstable idle, frequent stalling.
Oil in air cleaner.
Possible Cause
EGR valve hoses misrouted.
BVSV is out of order.
Possible Cause
PCV valve completely stuck.
Hose plugged.
PCV system plugged.
Correction
Check EGR valve hose routings.
Check BVSV. Replace as necessary.
Correction
Replace valve.
Check hoses.
Replace valve.
5-17