Page 41
240-2 Fuel injection system
Checking and adjustments
General
Before testing and fault tracing of the Cl system
is started, it must first be established that there
are no mechanical faults in the engine and that
the ignition system is functioning properly.
Scrupulous cleanliness must be observed during
work on the fuel system. The surrounding area
should be thoroughly cleaned before any lines
are disconnected.
Danger of fire
There is an acute danger of fire because of
fuel atomization in this test. Make sure
that there is good ventilation and that no-
body is smoking.
Fuel leakages
Check that there are no leakages at the connec-
tions and in the fuel lines. Check around the fuel
tank, in the passenger compartment and in the
engine compartment. New seals should be fitted
to any leaking connections. Damaged fuel lines
should be replaced.
Check that fuel pipes do not chafe against other
objects (particularly of plastic). Continuous
chafing against e.g. the dipstick tube, other fuel
pipes or the throttle cable can result in damage
to the fuel pipe.
S 2/426
—
Saab 900
Page 42
bE
=e
Fuel injection system 240-3
Air leakages
Check for leakage in the induction system be-
tween the air flow sensor and the engine. Air
leaking into the system may result in poor engine
performance, owing to the fact that it by-passes
the air flow sensor, causing a lean mixture.
Leakage can occur in the following places:
At the rubber duct between the air flow sensor
and the throttle housing.
At the gasket on the flange of the cold-start
valve.
At the gasket between the throttle housing and
the inlet manifold.
At the gasket between the inlet manifold and the
cylinder head.
At the hose connections to the throttle housing,
auxiliary air valve and inlet manifold.
Unwanted air can also be inducted via the crank-
case ventilation hose from the oil filler cap,
dipstick tube or camshaft cover gasket.
Air flow sensor lever mounting
Remove the rubber ducts and check the move-
ment of the lever in the air flow sensor. As the
arm is lifted, a steady resistance should be felt
as a result of the damping action of the control
plunger. No resistance should be felt when the
arm is suddenly pushed down when not acting on
the plunger. If the air flow sensor has not been
dismantled, use a pair of pliers ora magnet to lift
the lever. If any binding is felt, the air flow sensor
must be repaired.
Page 43
240-4 Fuel injection system
Air flow sensor plate clearance
Check that the clearance between the edge of
the air flow sensor plate and the air venturi is uni-
form.
Air flow sensor plate - rest position
Check the rest position of the air flow sensor
plate with the ignition switched off (fuel pump
not working). This prevents fuel being injected
into the cylinders when the sensor plate is lifted
from its rest position. The upper edge of the sen-
sor plate should be level with the bottom edge of
the air venturi. This is the highest permissible
position for the sensor plate. A position slightly
beneath the lower edge of the venturi (0.02in.,
0.5mm max.) is permissible. The measure-
ments should be taken from the middle of the
lever.
The rest position can be adjusted by bending the
clip (A) for the spring-loaded arm on the under-
side of the air flow sensor. The air flow sensor
must first be removed.
A B 5 sath
Sensor plate clearance
A Right
B Wrong
/ = he
0-05 mm
A
Saab 900
Page 44
Fuel injection system 240-5
Auxiliary air valve
(Must be carried out with the engine cold.)
If a subsequent check of the control pressure
with the engine cold is to be made, disconnect
the leads from the warm-up regulator to prevent
the bi-metal strip from heating up.
With the aid of a light and a mirror, check that the
orifice in the auxiliary air valve is elliptical.
Remove the fuel pump relay. To provide current
to the pump and the Cl system, connect a jump
lead between terminals 30 and 87 in the relay
holder. The aperture in the auxiliary air valve
should be completely closed after about five mi-
nutes.
If the auxiliary air valve has not closed check the
electrical supply. If voltage is present, measure
the resistance of the heating coil across the ter-
minal pins on the auxiliary air valve, which
should be approx. 40 ohm. If the valve is defec-
tive, fit a new one.
Warm-up regulator
Check the electrical leads to the warm-up
regulator as follows.
Unplug the connector from the warm-up
regulator and connect a multimeter across the
connector pins.
f Remove the fuel pump relay and connect a
jumper lead between terminals 30 and 87 in the
relay holder, to provide power to the fuel pump
and Cl system. Read off the voltage, which must
not be below 11.5V.
Check the continuity of the warm-up regulator
coil by connecting a multimeter in series with the
coil. If a continuity break is found, fit a new
warm-up regulator.
Saab 900
Page 45
240-6 Fuel injection system
Thermostatic time switch
When the engine is cold, with a temperature
below 45°C (113°F), the switch should close al-
lowing current to flow for some time (depending
on the actual temperature) when the starter
motor is running.
Check that the switch closes when the starter
motor is running by connecting a test lamp
across the terminals of the unplugged connec-
tor.
Because it is not possible to make a more accu-
rate check of the time the switch is closed or of
the temperature, if in doubt, fit a new switch.
As from 1986 models, the thermostatic time
switch is fitted on the thermostat housing.
Fuel pump capacity
The fuel pump capacity can be checked by
measuring the return fuel flow as follows, pro-
vided that the fuel filter is not blocked and that
the battery is well charged.
Attach a hose to the fuel return connection at the
air flow meter. Place the other end of the hose in
a jar or suitable container.
Remove the fuel pump relay. To provide current
to the pump and the Cl system, connect a jumper
lead between terminals 30 and 87 in the relay
holder.
Run the pump for 30 seconds, measure the
amount of fuel collected, and check against the
figure specified in the "Technical Data” Section.
lf the amount of fuel collected is below the
specified value, the following possible causes
should be investigated:
® Defective fuel pump
e Voltage drop in power supply to pump
© Clogged filter or blockage in fuel line
1 Thermostatic switch (cars with catalytic converter
only)
2 Thermostatic time switch
3 Auxiliary thermostatic switch
Saab 900
Page 46
£ Fuel injection system 240-7
Voltage across the fuel pump
Remove the round cover plate from above the
ie fuel pump in the luggage compartment and mea-
L sure the voltage across the positive and negative
pe terminals of the pump while it is running. The
- lowest permissible voltage is 11.5V.
rter
Injection valves - performance and seal-
ing
Check the injection valves as follows.
1 Remove the rubber duct from the air flow |
sensor.
2 Remove the injection valves from the inlet
manifold and place them in a suitable con-
tainer. The fuel pipes should remain con-
nected.
&
3 Remove the fuel pump relay. To provide cur-
rent to the pump and the Cl system, connect
a jumper lead between terminals 30 and 87 |
in the relay holder.
4 Fuel atomization: Raise the air flow sensor |
lever and check the spray patterns of the in-
jection valves. If atomization is poor refer to |
"Injection valves - to clean”.
T
Saab 900
Page 47
rR
240-8 Fuel injection system
Danger of fire
There is an acute danger of fire because of
fuel atomization in this test. Make sure
that there is good ventilation and that no-
body is smoking.
5 Valve sealing: Switch off the ignition. The
fuel system is now under shut-off pressure.
Wipe dry the injection valve nozzles, lift the
air flow sensor lever and check if leaks
occur. It should take at least 15 seconds for
a drop of fuel to form on the tip of the injec-
tion valve. If this is not the case refer to "In-
jection valves - to clean”.
Cold-start valve - performance and seal-
ing
Unplug the connector from the cold-start valve,
leave the fuel pipe connected and unscrew the
valve from the throttle housing.
Connect the plug on one end of a test loom to the
cold-start valve and the other end of each lead to
the main beam terminal of a headlamp and to
earth, respectively.
Remove the fuel pump relay. To provide current
to the pump and the Cl system, connect a jumper
lead between terminals 30 and 87 in the relay
holder.
Place the cold start valve in a container and have
an assistant switch the headlights to main beam
for a short time {30 seconds max.}. Fuel should
spray out of the valve during this period.
Dry the valve nozzle and run the fuel pump for a
further minute. No fuel must come out of the
valve during this time.
Saab 900
Page 48
x
Fuel injection system 240-9
Checking of pressures
General
Connect pressure gauge 83 92 516 as follows:
Disconnect the contro! pressure line from the
fue! distributor and connect the pressure gauge
between the fuel distributor and the line to the
warm-up regulator.
N.B.
The safety device for running the fuel pump is
controlled by a pulse sensor in the pump relay
which is actuated by the ignition pulses.
Remove the fuel pump relay. To provide current
to the pump and the Cl system, connect a jumper
lead between terminals 30 and 87 in the relay
holder.
Bleed the pressure gauge by repeated opening
and closing of the valve with the pressure fauge
pointing downwards and the fuel pump running.
Saab 900
Page 49
240-10 Fuel injection system
Control pressure: engine cold
The test must be carried out with the engine cold.
Do not run the engine immediately prior to the
test and make sure that it has been left standing
for some hours (ideally overnight). This is be-
cause the test procedure is only valid when the
engine is at ambient temperature.
Open the valve, disconnect the plug at the warm-
up regulator and switch on the ignition.
Compare the pressure gauge reading with the re-
commended pressure given in the temperature/
pressure graph. Refer to the test values in sec-
tion 022, "Technical data”.
lf the value differs, replace the warm-up reg-
ulator.
Control pressure: engine hot
Carry out this test when poor performance has
been experienced with the engine at normal
temperature.
Open the valve.
Connect the warm-up regulator plug (if previ-
ously disconnected).
Leave the ignition switched on until the pressure
ha s stabilized.
Refer to the test values in section 022, "Techni-
cal data”.
lf the value differs, replace the warm-up reg-
ulator.
Saab 900
Page 50
. Fuel injection system 240-11
Line pressure
Close the pressure gauge valve.
Run the fuel pump.
Refer to the test figures in Section 022, "Techni-
cal data”.
lf the line pressure differs from the recom-
mended figures, this may be due to one or more
of the following:
In the case of insufficient line pressure:
Insufficient pressure from the fuel pump
Blocked filter in the tank
Leak in the fuel pipe
Faulty line pressure regulator
In the case of excessive line pressure:
e Blocked return pipe
® Faulty line pressure regulator.
To adjust the line pressure, see "Adjusting the
line pressure” below.
Leakage tests on the whole system
This test should be performed when starting dif-
ficulties have been experienced when the engine
is hot.
If the engine is cold, the bi-metal strip in the
warm-up regulator must be heated and kept
warm during the test. Unplug the connector from
the warm-up regulator and connect a test loom
direct between the warm-up regulator and the
battery.
Open the pressure gauge valve. Run the fuel
pump until a reading equal to that for "Control
pressure: normal engine temp.” (Technical data
section) is reached, and then disconnect the
pump.
Note any drop on pressure on the pressure
gauge. Generally a leak becomes evident within
3-4 minutes. When in doubt maintain the system
under pressure for 20 minutes (see section 022,
"Technical data”). If the pressure falls too
rapidly, the fault can be located by performing
Saab 900