Page 101
240-72 Fuel injection system
Faults that can be traced to items 4 and 5 may
also be attributable to the limp-home function.
Fault symptom
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67
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234 8
234 6 9
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Possible cause
Temperature sensor
(NTC resistor)
Throttle butterfly failing
to open/close completely
Poor earthing or earth
connection or connection
wrongly wired
Broken cable or con-
nector
CO contenttoo low
CO content too high
Electronic control unit
or input signals
Check/Remedy
Check using an ohm-
meter
Check the throttle
housing, the throttle-
position sensor, spindle
and cable
Check the earthing of
the engine and battery
Check the wiring and
terminals and remedy
as necessary
Check the idling speed
and CO value as per
specification.
Check the resistance
(ohm reading) of the
airmass meter
Check the idling speed
and CO value as per
specification
Check the resistance
(ohm reading) of the
airmass meter
Check all input
signals and connections
of the electronic
control unit
Test procedure
E4
E5
E8A
EBA
E7C
E7C
E8A
Page 102
re
Fuel injection system 240-73
1 Engine fails to start
System or
component
a. Electrical
system
b. Fuel pump
c. Fuel system
d. Induction
system
e. Injection
valves
f. Temperature
sensor
(NTC resistor)
g. Electronic
control unit
h. Auxiliary air
valve
Possible cause
. Lowvoltage,
break in wiring,
poor connection,
faulty relay,
pressure switch.
. Fuel pump not
working or poor
capacity.
. Leakage, faulty
fuel pressure
regulator,
blockage in
return line.
. Airleakage
- Opening duration,
leakage
- Notfunctioning,
break in wiring,
poor connection.
. Poorcontact, no
input signals,
not functioning.
. Malfunction,
leakage.
Remedy
a. Check the battery voltage: minimum
acceptable value, 11.5 V. Check
system relay and pump relay E1,
E2. Check for breaks, poor con-
nections or corrosion inthe
wiring and terminals E8. Check
the pressure switch (TI urbo) E3.
b. Check fuel pump operation:
pressure capacity and flow. B1D,
Bie.
c. Check for leakage in the fuel
system B1. Check the line
pressure B1. Check the fuel
pressure regulator B1B.
d. Check for air leakage inthe
induction system: downstream of
throttle butterfly housing using
pressure testing equipment; and
visually between the air mass
meter and the butterfly. |4.
é, Check the opening duration of the
injection valves using a multi-
meterE6, E8B.
f. Check the temperature sensor using
a multimeter E4.
8. Check all input signals using a
multimeter, E84.
h, Check the auxiliary air using a
multimeter |2,
Saab 900
Page 103
240-74 Fuel injection system
2 Engine starts but stops immediately
System or
component
a.
Electrical
system
. Temperature
sensor
(NTC resistor)
. Induction
system
. Electronic
control unit
, Auxiliary air
valve
COcontenttoo.
low or too
high
. Idling system
(cars with cata-
lytic converter
Throttie-
position
sensor
Possible cause
. Lowvoltage,
break in wiring,
poorconnection,
faulty relay,
pressure switch.
. Notfunctioning,
break in wiring.
poor connection.
. Airleakage
. Poorcontact, no
input signals.
. Malfunction,
leakage.
. Incorrect
setting
. Incorrect
setting
. Incorrect
setting or
defective.
Remedy
_ Check the battery voltage: minimum
acceptable value, 11.5 V. Check
the system relay and pump relay
E1, £2. Check wiring and ter-
minals E8. Check the pressure
switch (Turbo) E3.
_ Check the temperature sensor using
a multimeter E4,
. Check forair leakage inthe
induction system: downstream of
throttle butterfly using pressure
testing equipment; and visually
between the air mass meter and the
throttle butterfly 11.
. Check all input signals using a
multimeter E8A.
_ Use a multimeter to check the
auxiliary air valve/idling-control
valve 12.
. Check the idling speed and CO con-
tent as per specification and
check the resistance of the air
mass meter E7C.
. Check idling speed and pulse
ratio against spec. Check
resistance of air mass meter {E7D).
_ Referto the section on checking
of the throttle-position sensor
ES.
Saab 900
Page 104
EE EE oO,
Fuel injection system 240-75
3 Erratic idling
System or
component
a.
Temperature
serisor
(NTC resistor)
. Aifmass
meter/CO
content
. Idling system
(cars with
catalytic
. Induction
system
. Injection
valves
Fuel system
, Electronic
control unit
. Auxiliary air
valve
Electrical
system
EGR valve
- Oxygen (Lambda)
sensor
Possible cause
a. Not functioning,
break in wiring,
poor connection.
b. COcontent set
too high ortoo
low. Broken
filament.
c. Incorrect setting
d. Leakage
6. Opening duration,
leakage
f. Insufficient
pressure,
g. Poorconnection,
no input signals
h. Matfunction,
leakage
i. Broken wiring
or faulty
connectors.
Poor earthing.
j. Notfunctioning.
Valve binding.
k. Poor contact.
Resistance
incorrect
Remedy
a. Check the temperature sensor using
multimeter E4.
b, Check the air mass meter- for
insufficient or excessive CO
content. Check that the filament
issoundE7C.
¢. Check idlingsspeed and pulse ratio
againstspec: Cheek resistance of
airmass meter E7D
d. Check for air leakage in the
induction system: using pressure
testing equipment. Vacuum should
be between -0.4 and -0.8 bar /1.
e. Check the opening duration and
resistance of the injection valves
using a multimeter E6, E8B.
f. Check fuel system line pressure
and pressure-regulator function
Bi.
g. Check all input signals usinga
multimeter ESA.
h, Check the auxiliary air valve
| oe
i. Check the wiring and connections
E8. Check the earth connections
onthe engine and battery.
|. Check the EGR system (see Section
2:4, subsection 254, of the
Service Manual),
k. Check the oxygen sensor E10
Saab 900
Page 105
I EISSSSSES'S'S''@'~S ~~ ii
Fuel injection system 240-77
5 Engine runs erratically at all speeds
System or
component
a. Electronic
control unit
b. Electrical
system
c. Injection
valves
d. Turbo/APC
e. Throttle-
position sensor
f. Airmass meter
g. Induction
system
h. Fuel system
i. Temperature
sensor
(NTC resistor)
j. Oxygen (Lambda)
sensor
Possible cause
. Defective
connection in
connector.
. Alternator. Low
voltage. Poor
earthing.
. Opening duration
. Malfunction
. Incorrectly
adjusted,
butterfly
binding
. Burn-off function
not working,
broken filament.
. Airleakage.
. Insufficient or
no fuel pressure:
Poor capacity,
i, Not functioning,
break in wiring,
poorconnection.
. Poorcontact.
Resistance
incorrect
Remedy
. Check terminals 9, 14, 13,17 and
25 inthe contro! unit for defec-
tive connections E8.
b. Check the operation of the alter-
nator (See section on electrical
system) and the battery voltage
E1, E2,€8.
. Check the opening duration of the
injection valves using a multi-
meterE6, E8B.
» Check the operation of the Turbo
(see Turbo section). Check the
operation of the APC (see APC
section).
- Check the throttle-position sensor
using 4 multimeter, that the
microswitch is correctly adjusted
and the butterfly is not Sticking
ES.
. Check the filament and thatthe
burn-off function is working E7,
- Check for air leakage in the
induction system: downstream of
throttle butterfly USIN€ pressure
testing equipment; and visually
between the air mass meter and
throttle butterfly.
. Check the line pressure inthe
fuel system B1.
. Check the temperature sensor using
a multimeter E4.
. Check the oxygen sensor E10
Saab 900
Page 106
ne
EI’
Fuel injection system 240-79
7 Engine fails to rev up (no power)
System or
component
a. Induction
system
b. Throttle
butterfly
c. Fuel system
d, Injection
valves
e. Airmass meter
f. Turbo/APC
g. Temperature
sensor
(NTC resistor)
h. Electrical
system
i. Electronic
control unit
Possible cause
o
>
. Leakage
. Incorrectly
adjusted
. Insufficient
flow/low voltage
. Malfunctioning
. Burn-off function
not working.
Broken filament.
Malfunctioning.
. Not functioning,
break in wiring,
poor connection.
. Broken wires or
connections:
Poor earthing or
earth contacts.
Poor connections,
no input signals
or signals weak.
Remedy
a. Check for air leakage inthe
induction system using pressure
testing equipment |.
b. Check that the butterf| yopens
fully ES.
¢. Check the flow from the fuel pump
B1E. Check pump power supply
(11.5V minimum) B1E,
d. Check the injection valves by
disconnecting the leads, oneata
time, which should cause the
engine speed to drop noticeably
E6, E8B.
e. Check the filament and that the
burn-off function is working E7.
f. Check the operation of the Turbo
(see Turbo section). Check the
operation of the APC (see APC
section).
&. Check the temperature sensor using
a multimeter E4.
h. Check the wiring and connections
E8. Check the earth connections
on the engine and battery.
i. Check all input signals usi nga
muitimeter E8.
Saab 900
Page 107
240-80 Fuel injection system
8&9 CO content too low or too high
System or
component
Induction
system
- Fuel system
Airmass meter
. Temperature
sensor
(NTCresistor)
. Electrical
system
Electronic
contro! unit
. EGRvalve
Possible cause
a. Leakage
. Leakage,
defective fuel
pressure
regulator,
blockage in
return
line/insufficient
flow,
. Burn-off function
not working,
broken filament,
. Not functioning
. Broken wires or
connections.
Poor earthing or
earth contacts.
. Poorconnections,
no input signais
or signals weak,
. Not functioning.
Valve binding.
Remedy
. Check for air leakage in the
induction system using pressure
testing equipment 11.
. Check the line pressure B1.
Check the fuel pressure regulator
by slowly pinching the return line
BiB. Check the flow B1D, B1E.
. Check the filament and that the
burn-off function is working E7,
. Check the temperature sensor using
a multimeter E4.
. Check the wiring and connections
E8. Checkthe earth connections
onthe engine and battery.
. Checkall input signals using a
multimeter E8.
. Check the EGR system (see Section
2:4, subsection 254, of the
Service Manual).
Saab 900
Page 108
EEE EIIISS'OS'SSSSSIS
Fuel injection system 240-81
Checking/fault diagnosis
LH injection system
A special tester unit for the LH system that ap-
preciably simplifies Servicing and fault-diag-
nosis work is available:
LH-system tester 83 94223
Service Manual supplement 401711 (GB)
40 17 78 (US)
For fault diagnoisis using the LH-systern tester,
see page 240-60.
Bi Checking the fuel system
Tools: LH fuel pressure gauge equipment
8393 852
Test hose for return flow
Graduated beaker, 2} (0.5 Usgal)
Jumper lead with switch 83 93 886
Cooling system pressure tester and hose
Vacuum pump
Pressure gauge 8393514
Multimeter
1 Disconnect the banjo coupling at the inlet to
the fuel injection manifold and connect the
fuel pressure gauge using the existing
Seals. Tie up the pressure gauge so that it
hangs vertically to obviate reading errors,
2 Remove fuse No, 30. Connect the jumper
lead and switch between fuse No. 30 and
fuse No. 27, 28 or 29, to provide current to
the fuel pump.
Make sure that the switch is set to OFF
B1A Checking the line pressure
1 Start the pump by setting the switch to ON.
The line pressure should now rise to the
specified value (see Section 0. Technical
data},
Line pressure too high:
Stop the fuel pump by moving the switch to
OFF. Disconnect the return line from the fuel
Saab 900
Page 109
| 240-82 Fuel injection system
pressure regulator and blow through the
line.
If the:line is open;
Change the fuel pressure regulator.
If the line is blocked:
Unblock it or fit a new return line. Check the
one-way valve at the tank.
/ Line pressure too low:
| * Check the level of fuel in the tank.
] ® Check for leaks in the fuel system.
e Check the fuel pressure regulator (see
next section).
BiB Checking the fuel pressure
! regulator
i 1 Connect pressure gauge 8393514 to the
| inlet amd outlet on the fuel pressure reg-
ulator. Tle up the pressure gauge so that It
hangs vertically to obviate reading errors.
Connect either the cooling system pressure
| tester or the vacuum pump to the pressure
" gauge (83 93514).
2 Start the fuel pump by moving the switch to
ON. The line pressure should now rise to the
specified value (see Section 0, Technical
data).
Use a vacuum pump to raise a vacuum in the
fuel pressure regulator. The amount by
which the line pressure drops should now
correspond to the movement of the needle
} on the pressure gauge (see Section 0).
Use the cooling system tester to raise the
pressure in the fuel pressure regulator. The
amount by which the line pressure rises
| should now correspond to the movement of
| the needle on the pressure gauge (see Sec-
| tion 0). :
Saab 900
Page 110
Fuel injection system 240-83
BiC Checking the residual pressure
Start the fuel pump by setting the switch to ON.
Read off the line pressure. For correct value, see
Section 0, Technical data.
Stop the fuel pump by setting the switch to OFF.
The pressure should immediately drop by 0.1 -
0.2 bar (1.5- 2.9 psi). If the drop in the residual
pressure during 10 minutes is greater than this,
check for leakage in the pressure regulator and
the fuel pump non-return vatve. Check the pres-
sure and flow delivered by the fuel pump.
B1iD Checking the fuel pump delivery
pressure
Start the pump by setting the switch to ON. Pinch
closed the return line momentarily.
There should be an immediate, marked rise jn
the line pressure.
Insufficient delivery pressure:
* Check that the voltage across the fuel pump
terminals is atleast 11.5 V.
Saab 900