Page 71
240-32 Fuel injection system
9 Preset the position of the adjustment arm.
10
11
Using a depth gauge, measure the distance
between the joint surface of the fuel dis-
tributor (across the screw holes) and the
needle bearing roller. The dimension should
be 18-19mm (0.71-0.75 in). To adjust the
dimension, turn the mixture adjusting screw
by means of an Allen key.
Fit the "0" ring and the fuel distributor. Fit
the lower plastic section of the air flow sen-
sor together with the gasket.
Tightening torque,
Fuel distributor screws
3.2-3.8 Nm (2.4- 2.8 Ibf ft)
Fit the mixture control unit in the car. Fine
adjustment of the basic fuel flow is made by
means of a CO gauge after the engine has
been warmed up.
Fine-tune the fuel/air mixture and replace
the plug over the adjusting screw in the air
flow meter (see page 240-15).
Replacing injection valves
4 Clean the area around the injection valve
and its connection.
2 Disconnect the fuel line from the valve. To
prevent the valve turning, hold the hexagon
with a spanner.
Saab 900
Page 72
Fuel injection system 240-33
3 Remove the retaining plate.
4 Withdraw the injection valve and pull off the
rubber seal.
Refit in the reverse order.
Injection valves - to clean
If an injection valve is atomizing the fuel impro-
perly or if it is leaking under opening or closing
pressure the cause can be small particles of dirt
in the valve seat. It is sometimes possible to re-
move the particles by forced flushing of the valve
as follows:
1 Disconnect the rubber ducts from the air
flow sensor.
2 Remove the injection valve from the inlet Perfect atomization Acceptable atomization
manifold and place it ina suitable container.
Do not disconnect the fuel line.
3 Remove the pump relay and use a jumper
lead across terminals 30 and 87 in the relay
holder to provide power to the fuel pump.
4 Raise the air flow sensor lever a few times to
its highest position, thereby force-flushing
the injection valve.
Examples of poor atomization
Saab 900
Page 73
240-34 Fuel injection system
Injection valves that have been removed
from the car can also be cleaned by means
of an injector tester designed for diesel
equipment (e.g. Bosch KDJE P400 or KDJE
7452). Cleaning with compressed air is not
recommended.
If the fault persists, fita new injection valve.
Replacing the warm-up reg-
ulator
1 Clean the area round the warm-up regulator
and its connections.
2 Disconnect the electrical leads and both
fuel pipes from the regulator.
3 Remove the regulator.
Refit in the reverse order.
Replacing the auxiliary air valve
1 Pull off the hoses and unplug the electrical
lead.
2 Unscrew the auxiliary air valve.
Refit in the reverse order.
Page 74
Fuel injection system 240-35
Fuel accumulator
To remove
1 Cleanthe area around the fuel connections.
2 Undo the connections and remove the fuel
accumulator.
To refit
1 Mount the accumulator on the bracket on
the fuel tank.
2 Connect the fuel lines. The line from the fuel
pump should be fitted to the connection
nearest to the edge of the fuel accumulator.
Make sure that the fuel line from the pump can-
not chafe against the body.
Replacing the fuel filter
1 Clean the area around the two connections.
2 Hold the filter by means of the hexagons on
the filter and fitting and disconnect the fuel
lines. Remove the filter.
N.B.
Avoid loosening the fitting on the outlet side to
prevent aluminium swarf from the threads enter-
ing the system.
3 Fit the new filter with the arrow pointing in
the direction of flow and connect the fuel
lines.
i
tf
!
Page 75
240-36 Fuel injection system
Cl fuel injection system,
Lambda (EU & US specs)
A general description of the oxygen-sensor
(Lambda) system fitted to cars with catalytic con-
verters is given on page 200-16.
When using the component locations or fault-
diagnosis chart included in this section, refer at
the same time to the wiring diagram in section
3:2 of the Manual.
Fuel shut-off on deceleration (1987)
Manual cars with normally aspirated engines are
equipped with a system that shuts off fuel injec-
tion during engine overrun. The system is pro-
vided to reduce fuel consumption and also the
content of unburned hydrocarbons (HC) in the
exhaust. The system comprises a vacuum valve
and a deceleration relay.
Principle of operation
The deceleration system causes the induction
air that normally flows across the air flow sensor
plate to bypass the sensor plate via a hose and
vacuum valve, resulting in the sensor plate re-
maining in its home position and hence shutting
off the flow of fuel to the cylinders.
Air cleaner and fuel distributor
From deceleration relay
Vacuum valve
From inlet manifold
Sensor plate in home position
Bypass line
Rubber socket connector
Filter
Fuse
OANDOFWNHe
$21363
Saab 900
Page 76
Fuel injection system 240-37
Thus, the vacuum valve acts as a bypass line
when the deceleration system is operating. Be-
cause the relay is operating, the ECU selects a
fixed pulse ratio of 60%.
The deceleration relay operates when:
¢ the thermostatic switch is closed (coolant
temperature above 45 °C/113 °F)
the time relay (P11) is not operating (relay in
de-energized position)
e the engine speed is higher than 1575 + ]
175rpm. 5
¢ the throttle-position sensor is making the cir-
cuit
The deceleration system shuts off the supply
of fuel as soon as the set of contacts in the
throttle-position sensor close (foot off ac-
celerator). '
Fuel supply is resumed once the engine speed
has fallen below 1375 + 75 rpm.
fell
Principle of operation of fuel shut-off system
Time relay for boost during acceleration
Deceleration relay (manual cars)
Throttle-position sensor
Lambda ECU
Vacuum valve
Hose from inlet manifold
Fuse
Ignition coil
OBrADOfWNHE
Vacuum valve mode of operation
When current flows through the vacuum valve
solenoid (4) from power distribution panel (2) via
the deceleration relay (3) to earth, the depres-
sion in the inlet manifold acts on the diaphragm
in the valve, opening the bypass port.
Vacuum valve
Page 77
240-38 Fuel injection system
Single-function throttie-position sensor
(normally aspirated engines)
Contact is made between terminals 1 and 2 only
when the butterfly is in the position for idling.
When the circuit is made, terminal 30 in the de-
celeration relay and terminal TRK in the time
relay receive an earth signal (further details are
given in the description of the relay operation).
Once the throttle butterfly has opened beyond
72°, contact is made between terminals 2 and 3,
an earth signal is received from terminal TK in
the AC relay (156) and the electromagnetic
clutch on the AC compressor is disengaged (cars
with AC only).
Dual-function throttle-position sensor
(Turbo)
Contact is made between terminals 1 and 2 when
the throttle butterfly is between the position for
idling and an opening angle of 72°. During this
time, terminal 31A in the speed relay receives an
earth signal (further details are given in the de-
scription of the TIP relay operation),
After the throttle butterfly has moved beyond the
72° opening angle, contact is made between ter-
minals 2 and 3, This makes the earthing circuit
to terminal TK in the AC relay (156) (releasing the
electromagnetic clutch on the AC compressor),
to terminal 11 in the deceleration relay (106)
and thence to terminal 11 in the Lambda ECU,
thereby providing a pulse ratio of 92% minimum.
Throttle-position sensor on normally aspirated
engine
Throttle-position sensor, Turbo
Saab 900
Page 78
om |
2
[saaset ] 7) |
ww
Qa
a a, Se |
Fuel injection system 240-39
Thermostatic switch (45/38 °C) and ther-
mostatic time switch
The thermostatic switch is closed at tempera-
tures below 45°C (113°F}. If the temperature
has been higher than this, the switch will not
close until the temperature has fallen to 38°C
(100 °F). The thermostatic switch is connected in
series with the thermostatic time switch (92),
Thus, no earthing is available for the cold-start
valve or terminal TKK in the time relay (106) at
temperatures above 45°C (113°F).
Thermostatic switch (25/18 °C)
The thermostatic switch is closed at tempera-
tures below 25°C (77 °F). If the temperature has
been higher than this, the switch will not close
until the temperature has fallen to 19°C (66 °F).
Normally aspirated. engines
The switch is connected in parallel with terminal
12 in the Lambda ECU via terminal X11 in the de-
celeration relay.
At temperatures below 25°C (77°F), an earthing
signal is available to terminal 12 in the Lambda
ECU and a pulse ratio of 60% is selected (the
same as during fuel shut-off via P12)
At temperatures above 25°C (77°F), the ther-
mostatic switch is open and the preset pulse
ratio is not selected.
Turbo engines
The function is the same except that the ther-
mostatic switch is connected direct only to termi-
nal 12 in the Lambda ECU. A fixed pulse ratio of
60% is selected.
1 Thermostatic time switch (99)
2 Thermostatic switch (92)
3 Thermostatic switch (97)
Saab 900
Page 79
240-40 Fuel injection system
Lambda ECU
The ECU controls the oxygen-sensor-regulated
system by means of the following main func-
tions:
* Oxygen-sensor monitoring
* Comparator
e |ntegrator
Output stage (signal amplifier)
S$2/1366
a BCU 135 Hel
| Comparator Integrator |
| Oxygen-sensor Output stage
monitoring |
Oxygen sensor Modulating valve
na Exhaust gases
The monitoring function checks that the opera-
tion of the oxygen sensor and the modulating
valve control function coincide with the program-
med values. If incorrect values are received or a
malfunction is detected, e.g. in the oxygen sen-
sor, the control function is disabled and a fixed
pulse ratio (50%) is selected for the modulating
valve.
Different fixed pulse ratios can also be selected
if certain terminals in the ECU are earthed.
The control function of the comparator is gov-
erned by the relationship between the actual
sensor voltage and the preprogrammed refer-
ence voltage in the comparator.
If the mixture is lean, the signal voltage from the
oxygen sensor will be lower than the reference
voltage and the ECU will then increase the pulse
ratio (opening duration) of the modulating valve,
thereby enriching the mixture.
The integrator controls the signal voltage from
the output stage at a programmed control speed
to enrich or weaken the mixture. The control
speed is optimized to provide best possible con-
version of the exhaust gases in the catalytic con-
verter, by keeping the Lambda value between
very tight limits, as close as possible to
Lambda = 1 (ideal mixture).
Saab 900
Page 80
Fuel injection system 240-41
Lambda ECU terminal pins
Pin 2 Signal from oxygen sensor 136.
Green (GN).
Pin 4 Oxygen sensor. Screened braid.
Pin 15 Pulsed earth signal to modulating
valve 139. Dependent on pulse
ratio. Violet (VL).
Pin 17 + 12V supply via fuse 8 from termi-
nal +54 on power distribution
panel. Brown/white (BR/VT).
Pins + 12V supply when fuel pump relay
102 operating. Yellow/red (GL/RD).
Pin 26 Internal jumpering. Yellow (GL).
Pin7 When earthed, fixed pulse ratio of
85%. Red/white (RD/VT).
Pin 12 When earthed, fixed pulse ratio of
60%. Yellow/red (GL/RD).
Pin 11 When earthed, fixed pulse ratio of
92% minimum. Red (RD).
Pin 16 Earthing point. Black/white (SV/VT).
Pin 5 Earthing point. Brown (BR).
Fuel-booster pressure switch
With the car being driven at a steady speed, the
depression on either side of the diaphragm is
equal. During acceleration, the depression
weakens, and because of the restriction the
pressure change below the diaphragm is de-
layed. The momentary increase in "absolute”
pressure acting on top of the diaphragm pushes
the diaphragm down, actuating the spring con-
tact and making the circuit.
1 Diaphragm
2 Spring
3 Restriction
4 Spring contact
5 Vacuum inlet
6 Electrical terminals
Saab 900