Page 131
240-104 Fuel injection system
3 |f the engine speed drops noticeably, check
the following:
*® The power supply to terminal 16 (red/
white; RD/VT) on the ECU.
® If no power is present, check the red/
white (RD/VT) lead from terminal 16 on
the ECU to terminal 16 onthe AC relay and
| also check that the relay is operating
properly.
If voltage is present:
e Check the yellow/red (GL/RD) lead from
terminal 3 on the AIC valve to terminal 23
on the ECU connector, and the blue/white
(BL/VT) lead from terminal 9 on the AIC
valve to terminal 10 on the ECU connec-
tor.
e Check the AIC valve |3.
® If the AIC valve is sound, try fitting a
| known good ECU.
E10 Checking the oxygen (Lambda)
sensor
The oxygen sensor provides one of several input
signals that the ECU processes to determine the
proper air-fuel ratio. Other inputs include engine
rpm, engine temperature, throttle position and
air mass.
The oxygen sensor used with the LH system has
an electric preheating function which enables it
to quickly reach a temperature that allows accu-
rate measurement of exhaust gas composition.
| 1 Unplug the two-pin connector from the wir-
ing loom.
2 Use the multimeter to check the resistance a 6 ine
| across the two white terminals on the sen- Beocteat
\ sor. The reading should be approx. 4 ohm. a
3 Using the DCV 2-V scale, connect the mul- Rerum! tae fo, ol eae, Pa ok
timeter across the oxygen sensor black lead sis dea he as ABR GR it ae 2
and earth,
Start the engine.
As the sensor comes up to temperature, it
| starts to generate a low-voltage signal of be-
Saab 900
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Fuel injection system 240-105
tween 100 and 900 mV, The actual signal
varies with the strength of the mixture: a
lean mixture, such as that caused by a slight
vacuum leak, will give a Lambda value of 1
and a sensor voltage of about 100 mV.
Arich mixture will give a Lambda value of <1
and a sensor voltage of about 900 mV.
11 Checking the induction system
Tools: Pressure gauge set 8393514
There must not be any leakage of air between the
air mass meter and the engine.
1 Check the hose connections on:
* the auxiliary air valve
® the brake servo unit
* the vacuum chamber
® the pressure switch
the EGR thermostatic valve
the EGR valve
© the fuel pressure regulator
Also check:
® that the butterfly closes
* thatthe three securing bolts for the throt-
tle housing are tight
2 Check that the injection valves are properly
seated in the inlet manifold and that the 0”
rings are not damaged.
If after the completion of these checks air
leakage is still Suspected, carry out further
checks as follows:
3 Connect pressure gauge 8393514 to the
inlet manifold, downstream of the throttle
butterfly, and hang the pressure gauge on
the rear-view mirror inside the car,
4 Start the engine and let itrunat idling speed
(850 50 t/min). Check the vacuum, which, if
the system is operating correctly, should be
betweeen -0.4 and -O.8bar (-5.8 and -
10.2 psi). If the vacuum is less than -0.4 bar
(-5.8 psi}, check the system again as de-
tailed in step 1 above.
5 Check for air leakage in the induction sys-
tem, using the pressure gauge to check
downstream of the throttle butterfly, and
making a visual check between the air mass
meter and the butterfly. The vacuum should
be above -0.4 bar (-5.8 psi).
Saab 900
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240-106 Fuel injection system
6 Make a visual check also for air leaks be-
tween the throttle housing and pressure
pipe, between the pressure pipe and the
turbo, between the turbo and the inlet man-
ifold, at the inlet manifold connections for
crankcase ventilation and the APC return
hose.
Check also the rubber duct connections be-
tween the inlet manifold and the air mass
meter, and the connections between the air
mass meter and the air cleaner, at the air
cleaner cover and between the air intake and
the air cleaner.
i2 Checking the auxillary air valve
(When fitted)
Tools: Multimeter
Torch (flashlight)
Mirror or sheet of white card
Jumper leads
Before performing any checks on the auxiliary air
valve, unplug the electronic contro! unit and
auxiliary air valve connectors.
N.B
Checking must only be done when the engine is
cold (temperature below 30 "C/BG6 °F),
4 Using two separate jumper leads, connect
pin 21 (yellow/white; GL/VT) and pin 17 (vio-
let; VL) on the ECU connector to earth.
2 Check that voltage is present across the
auxiliary air valve terminals, If not, check
that the system relay and pump relay are
operating properly E1 and E2 and check the
grey and black (GR; SV) leads to the auxiliary
air valve.
3 Detach the rubber hoses and plug in the
auxiliary air valve connector. Check that the
valve opens by shining the torch through one
of the hose spigots and holding a mirror or
sheet of white card close to the opening in
the other hose spigot. The valve should
close fully after about five minutes (depend-
ing on the temperature of the engine).
4 If not, check the resistance of the auxiliary
air valve by connecting the multimeter
across the valve terminals. The reading
should be 40- 60 ohm. If the reading ob-
tained is not between these values, fit anew
auxiliary air valve.
Page 134
Fuel injection system 240-107
13 Checking the AIC valve
* Unplug the connector from the AIC valve.
Measure the resistance across pin 3and pin 2
(the middie pin) on the valve and between pin
2 and pin 1. Refer to the "Technical Data” sec-
tion for the correct resistance value.
If the correct reading is not obtained. try fit-
ting a new AIC valve.
M1 Basic setting of throttle butterfly
! ip 1 Check that the butterfly is mounted centrally
in the throttle housing.
2 Screw in the adjusting screw until it touches
« a) the stop (butterfly fully closed).
3 Turn the adjusting screw a further 1/3 turn
and lock the screw with the nut. This will set
a clearance between the butterfly and the
throttle housing of approx. 0.05mm
{0.002 in).
4 Check the length of the throttle cable to en-
sure that it will not prevent the butterfly from
reaching the position for idling speed, and
that there is no play atthe accelerator pedal,
5 Check that the butterfly opens fully when the
accelerator is depressed to the full-throttle
position.
Check and adjust the throttle-position sen-
sor.
M1A Adjusting the idling speed
(N/A cars with catalytic converter)
The idling speed is adjusted by means of the ad-
justing screw on the by-pass passage for the
throttle housing. Adjust the idling speed in con-
junction with setting the CO value.
Idling speed: 850 + 75 r/min
N.B
The engine must be at normal temperature.
Saab 900
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240-108 Fuel injection system
MiB Setting the idling speed
(cars with catalytic converter)
Setting the idling speed involves the use of
| either a dwell angle tester and tachometer or the
LH-system tester.
Before starting work on the AIC, system, check
the ignition timing and CO setting (Lambda set-
ting on US spec, cars),
Tools
| Dwell angle tester and tachometer
or
Digital inductive dwell meter and
tachometer 4
or
LH-system tester Throttle stop locknut T-wrench
8394322
N.B
The accuracy of the dweil angle tester and the di-
gita| inductive dwell meter should be =+0.5%.
1 Start the engine and run it up to normal
temperature. (It is vital that the gearbox oil
be hot.)
2 Undo the locknut on the throttle and lower
the dashpot clear of the throttle lever.
When using a dwell angle tester:
3 a Pull back the rubber on the AIC valve con-
nector and connect the dwell angle tester
probes to pins 4 and 5 (valve terminals 2
and 3).
Connect the tachometer.
Saab 900
Page 136
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Fuel injection system 240-109
When using a digital inductive dwell meter
3 b Pull back the rubber boot on the AIC valve
connector, Insert probe into pin 3 (valve
terminal 5) and connect lead of dwell
meter.
Connect the tachometer.
When using the LH-system tester:
3 ¢ Undo the LH ECU securing screws and
connect the LH-system tester between
the ECU and the ECU wiring-loom connec-
tor.
i Mt 4 Unplug the connector for the throttle-posi-
| tion sensor and connect a jumper lead be-
tween pins 1 and 2 on the back of the con-
nector (terminals 2 and 18 on the throttle-
position sensor). This simulates closed con-
~ tacts for the idling position.
lf the setting is made with the contacts
open, the value will be incorrect.
5 Undo the two retaining serews for the throt-
y tle-position sensor and rotate the sensor
clear of the throttle butterfly. Make sure that
the throttle cable is slack so that it cannot
| interfere with movement of the butterfly.
6 Start the engine and isolate all possible
loads, such as the AC system, headlights,
| seat heaters, etc.
N.B
Setting must not be carried out when the radiator
fan Is running.
Saab 900
Page 137
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240-110 Fuel injection system
Cars not fitted with air bleed screw:
7 a Slacken the throttle stop screw locknut
and tum the adjusting screw anti-
clockwise until it no longer touches the
throttle linkage.
N.B
The meter reading should increase toa minimum
of 34° or 38%.
lf difficulty is encountered in obtaining this
value, check for air leaks in the Induction system
downstream of throttle housing or improperly
centred throttle butterfly.
Cars fitted with air bleed screw:
7 b If necessary (i.e. if the correct setting
value for the AIC valve cannot be ob-
tained), adjust the position of the throttle
butterfly (it must be properly centred) by
slacken|ng the throttle stop screw locknut
and turning the adjusting screw until it
just touches the linkage (throttle fully
closed).
Turn the screw a further 1/3 turn (US
spec.; 1/2-3/4 turn) and tighten the
locknut. This sets a clearance between
the butterfly and housing of approx. 0.05
mm (0.0020 in).
Slacken the air bleed screw locknut and
turn the air bleed screw In (clockwise)
until fully seated,
N.B
The meter reading should increase toa minimum
of 34° or 38%.
If difficulty is encountered in obtaining this
value, check for alr leaks in the induction system
downstream of throttle housing or improperly
centred throttle butterfly.
Saab 900
i
© 4
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Fuel injection system 240-1114
8 Turn the adjusting screw/air bleed screw
slowly clockwise so the AIC valve setting de-
creases.
When the reading shows the correct setting
value, the idling speed should be 850 r/min.
N.B
When using the LH-system tester, make the ad-
justment slowly to give the tester time to perform
the necessary calculations.
AlC-valve setting values
Using LH-system
tester or dwell
Using dwell angle angle tester with
tester (degrees) * % scale
32+4 3544 New cars <1000 miles (1500 km)
304141 33% 1 Cars with mileage >1000 miles
(1500 km)
9 Tighten the locknut on the adjusting screw?
air bleed screw taking care not to alter the
setting.
10 Switch off the engine.
11 Reset the throttle-position sensor (closed in
idling position).
Saab 900
Page 139
240-112 Fuel injection system
Check the setting: move the throttle lever
and if the setting is correct a light metallic
click should be heard as the sensor switches
from the idling position. Do not confuse this
with click from upshift switch.
42 Set the throttle dashpot to close within a
period of 4 + 1 seconds and then tighten the
locknut.
13 Remove the jumper lead from the throttle-
position sensor connector and plug the con-
nector onto the sensor.
14 Remove the probes from the AIC valve con-
nector and push back the rubber boot.
If the LH-system tester has been used, un-
plug the connector and refit the LH control
unit.
45 Turn the AC on and ensure that the idling
speed increases slightly.
Saab 900
Page 140
Fuel injection system 240-113
Component replacement
Electronic control unit (ECU)
1 Disconnect the negative (-) battery lead.
2 Remove the sill scuff plates from the right-
hand side of the car. Pull away the lower,
leading edge of the door weatherstrip.
3 Remove the plate which holds the carpet in
position on the wheel arch, and fold back the
carpet.
4 Unplug the ECU connector by releasing the
fastener and lifting the connector diagonally
upwards and outwards.
« in ) 5 Remove the screws securing the ECU to the
wheel arch,
Refit in the reverse order.
! System relay and pump relay
and fold it down out of the way.
1 Remove the securing screws for the air duct
2 Fold back the sound-insulation felt.
|
3 Pull the relays out of their holders.
To check the operation of the relays, detach
the relay holders from the wheel arch and
pull the relays forward; this will provide
much easier access to the electrical connec-
tors.
y
nt ) Refit in reverse order.
\
.
A
Temperature sensor
1 Detach the clips for the crankcase ventila-
tion hose from the camshaft cover.
2 Remove the fuel pressure regulator com-
plete with bracket from the cylinder head.
3 Unplug the connector from the temperature
sensor.
4 Drain off approx. 41 (4 tiqqt) of coolant to
prevent liquid running out of the aperture
after the sensor has been removed.
Saab 900