Page 51
240-12 Fuel injection system
the test with the pressure gauge valve shut.
If the figures obtained from this test are correct
then the shut-off valve in the warm-up regulator
is defective.
If the pressure drop is stil! excessive, the follow-
ing components could be faulty:
¢ The fuel pump non-return valve
¢ The fuel distributor
¢ The cold-start valve.
Leaks can occur if the "O” ring in the line pres-
sure regulator is damaged. To replace the "0"
ring see the sections, "Fuel distributor”, and
"Line pressure regulator”.
Adjusting the line pressure
After replacement of the "O” ring in the line pres-
sure regulator, the line pressure must be
checked and adjusted if necessary.
The pressure can be increased by fitting addi-
tional shims and decreased by removing shims.
Shims are available in thicknesses of 0.1 and
0.5mm. A 0.1-mm shim produces a change in
pressure of 0.15 bar (2.2 psi).
A prerequisite for measuring and adjusting the
line pressure is that the fuel pump capacity is
correct.
Screw plug tightening torque:
13 - 15 Nm (9.6 - 11.1 Ibf ft)
z
: 3
o
Line pressure regulator
1 Piston with "O” ring
2 Spring
3 Adjusting washers
4 Screw plug with "O” ring and sealing washer (con-
tains a stop valve for the fuel return from the warm-
up regulator/boost control circuit)
Saab 900
Page 52
Ss Fuel injection system 240-13
Idling adjustment
(engine speed and CO value)
Run the engine to normal temperature and then
connect the CO meter and the tachometer,
Speed setting
Adjust the idling speed by means of the adjust-
ment screw located on the by-pass passage in
the throttle housing.
N.B.
If rough idling or difficulty in reducing the idling
speed is encountered, check the setting of the
deceleration valve (see section 254),
Adjusting the CO value
The orifice in the fuel distributor is sealed by
means of an anti-tamper plug which must be re-
moved (and thereby destroyed) before adjust-
ment can be carried out.
A suitable tool can be made by brazing a5 mm
(0.20 in) self-tapping screw onto a screwdriver.
Be Grind a fine point on the screw and use the tool
e 1 as an extractor.
re.
&
5
‘on-
rm-
Caution
Remove the Allen key from the adjustment
screw after each adjustment. If the key is
left in the screw and the engine rewed up,
the lever can be damaged.
Saab 900
Page 53
240-14 Fuel injection system
Turning clockwise = richer mixture.
Turning anticlockwise = leaner mixture.
After adjustment, seal the orifice by means of a
new plug.
Connection of exhaust
extraction equipment
When using exhaust extraction equipment in the
workshop, avoid excessive depressurization of
the cars exhaust system, as this may affect
readings, e.g. of the CO content.
if excessively powerful exhaust extraction equip-
ment Is connected to turbo cars, oil may escape
through the seals in the turbo unit, resulting in
the exhaust system becoming saturated with oil,
and blue smoke being emitted in the exhaust for
some considerable time afterwards.
To avold excessively powerful exhaust extrac-
tion, connect a hose with an open coupling.
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Saab 900
Page 54
Fuel injection system 240-15
Setting the fuel-air mixture
Cars with catalytic converter
General
The air flow sensor adjusting screw is sealed by
a metal plug to prevent inadvertent alteration of
the setting. The mixture-screw is preset at the
factory and should not require resetting unless a
new air flow sensor has been fitted.
It may, of course, be necessary to reset the mix-
ture in conjunction with overhaul of the air flow
sensor or if the mixture is found to be incorrect
during fault diagnosis.
Setting a new air flow sensor
To gain access to the adjusting screw, remove
the air flow sensor and sensor plate arm to ena-
ble the metal plug to be removed from over the
adjusting screw.
1 Run the engine to normal temperature and
then connect the pulse ratio meter.
2 Set the engine idling speed to 875 + 75r/
min.
3 Set the specified pulse ratio using special
key 83 92 482.
Rev the engine and allow the idling speed to
stabilize before each reading.
The specified pulse ratio is given in the "Techni-
cal Data” section.
After completion, refit the plug using a drift to
drive it home.
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Page 55
240-16 Fuel injection system
Checking the _ fuel-boosting
function, Turbo cars, 1982
models and earlier
(N/A to cars with APC)
A Heavy load (not full throttle)
1 Run the engine at idling speed with the CO
meter connected (engine at normal temper-
ature).
2 Disconnect the pressure hose from the
throttle housing and connect gauge
8393514 (pressure gauge for testing the
charging pressure) and a cooling-system
tester to the hose. Plug the end of the spigot
on the throttle housing.
3 Raise the pressure to 0.80bar (11.6psi) -
because of the influence of the delay valve,
keep checking the reading on the gauge
until the pressure has stabilized.
4 Check that the CO reading has now risen to 4
- 6%.
B Full throttle
5 Disconnect the pump (cooling-system tes-
ter) and check that the CO reading returns to
its original value.
6 Push in the throttle-switch actuator.
7 Check that the CO reading increases to 4-
6%.
$ 7156
Saab 900
Page 56
Fuel injection system 240-17
Checking the residual pressure
If fuel boosting on acceleration is to be initiated
without delay, the pressure vessel and connec-
tions must be tightly sealed. In the event of ex-
tensive leakage, fuel boosting will not take place
until the charging pressure has built up.
1 Connect gauge 8393 514 (for checking the
charging pressure) between the non-return
valve and the pressure vessel.
2 Connect a cooling-system tester upstream
of the non-return valve and raise the pres-
sure to 0.8 bar (11.6 psi).
3 Wait five minutes and then check that the
pressure has not fallen below O.6bar
{8.6 psi).
Checking the fuel-boosting
function Turbo APC cars, M82
onwards
* Run the engine at idling speed with the CO
meter connected (engine at normal temper-
ature).
e¢ Disconnect the pressure hose from the
throttle housing and connect gauge
8393514 (pressure gauge for testing the
charging pressure) and a cooling-system tes-
ter to the hose. Plug the end of the spigot on
the throttle housing.
e Raise the pressure to 0.6 bar (8.6 psi).
si
Saab 900
Page 57
240-18 Fuel injection system
® Check that the CO reading increases to ap-
prox. 1- 6%.
To check the operation of the warm-up
regulator
Connect pressure gauge 83 92 516 as follows:
¢ Disconnect the control pressure line from the
fuel distributor and connect the pressure
gauge between the fuel distributor and the
line to the warm-up regulator.
e Disconnect the hose from the throttle housing
and connect pressure gauge 8393514 (for
checking the charging pressure) and a cool-
ing-system tester (air pump) to the hose. Plug
the end of the spigot on the throttle housing.
e Start the engine and run it until it reaches nor-
mal temperature.
® Raise the pressure to 0.6 bar (8.6 psi).
© Check that there is a drop in the control pres- (bar)
sure (see adjacent graph). P
S 7156
Contro! pressure
sii a
Boost pressure
02 04 06
08 (bar)
Saab 300
Page 58
Fuel injection system 240-19
Adjusting the throttle stop
1 Check that the throttle butterfly is in the
centre of the housing.
2 Turn the adjusting screw until it just makes
contact with the stop (throttle completely
closed).
3 Turn the adjusting screw another 1/3 turn
and tock it. This provides a clearance of
0.05mm (0.002in) approx., between the
butterfly and the housing.
Fault diagnosis
In the fault-diagnosis procedure described
below it is assumed that the engine does not
have any mechanical faults and that the ignition
system is working properly.
Starting difficulties: cold engine . . . 240-19
Starting difficulties: hotengine .. . 240-20
Poor drivability during warm-up period . 240-22
Poor drivability - engine at normal
LenMeratereitse: so ifaic. yo y f 240-23
Poor performance/low top speed . . . 240-24
Excessive fuel consumption .... . 240-26
Erratic CO value and idling speed,
difficulty inadjusting ........ 240-27
Starting difficulties: cold engine
1 Check the operation of the cold-start valve.
Remove the valve and place it in acontainer.
Fuel should be ejected from the valve when
the starter motor is switched on with the en-
gine colder than 45°C (118 °F). The injection
time depends on the temperature.
In the event of failure, check:
The cold-start valve
The thermostatic time switch
The electrical system
2 Measure the line pressure with the engine
cold. See secton "Technical data” for correct
value.
Saab 900
Page 59
240-20 Fuel injection system
3 Check that the auxiliary air valve is open
when the engine is cold.
4 a Check the CO-value (engine at normal
temperature).
b Check the pulse ratio (see section 2:4,
subsection 254, of the Service Manual
for US-spec. cars).
5 Check for air leakage between the air flow
sensor and the engine.
Starting difficulties: hot engine
If the pressure in the injection lines falls too low
while the engine is still hot, vapour bubbles can
form in the system, causing starting problems.
1 a First check that the connections on the in-
jection valves and fuel lines are tight.
b Perform the leakage test. First check with
the pressure gauge valve open. If leaks
are detected perform the test with the
valve shut (warm-up regulator discon-
nected).
Possible leakage points:
Fuel pump non-return valve
Warm-up regulator "0" ring
Cold start valve
External leakage
Stop valve for fuel return from the warm-
up regulator
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Saab 900
Page 60
me
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Fuel injection system 240-21
2 Open the valve and check the control pres-
sure (engine hot).
3 a Check the CO-valve (engine hot).
b Check the pulse ratio (Section 2:4, sub-
section 254, of the Service Manual for
US-spec. cars).
Check the hot-start relay (see "Cold-start
240-8}.
4 Check the rest position of the air flow sensor
plate in the air flow sensor. (The top of the
sensor plate should be level with or slightly
lower than max. 0.5mm; 0.02 in the lower
edge of the air venturi.) Adjust by means of
the spring (A)
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Saab 900