Page 191
ELECTRONICALLY CONTROLLED FUEL INJECTION
Contents Special testing devices and tools are required for repairing
the electronically controlled fuel injection system (page
Page 234—6 up to and 234-11).
including 10 1. Description of System In case of trouble the complete component (except igni-
Page 234—11 2. Testing Instruments and tion distributor) is to be replaced instead of repairing.
Tools Required
Page 234—11 up to and
including 20 3. Testing the Fuel Injection
System with Test Instrument Parts of pages 234—6 to 234—29 inclusive are reproduced '
EFAW 2285S 10 by kind permission of the copyright holder, Robert Bosch
Page 234—22 up to and Aktiebolag.
including 23 4. Fault Chart, Cause-Remedy
Page 234—24 up to and
including 29 5. Removal, Installation and
: Adjustment of the Individual
Components in the System
ENGINE COMPARTMENT
Nov. 1972 Sengey 234-4
Page 192
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Page 193
1. Description of System
1.1 Fuel system
Fuel is drawn by the electric fuel pump @ from the tank ©
via the filter @ and forced into the fuel pressure line.
The pressure regulator @ connected to the end of the
pressure line limits the fuel pressure. The electro-magne-
tic fuel injectors ® as well as the start valve @ are con-
nected to the pressure line by means of the fuel distri-
butor pipes ©. From the pressure regulator the excess
fuel can flow back to the tank through the return line.
The return line coming from the pump also leads into
the tank. A relief valve is fitted in the fuel pump which
opens if, due to a fault in the pressure system, the pres-
sure reaches a value much above that requires. A check
valve in the pressure connection of the fuel pump pre-
vents a complete loss of pressure in the fuel line when
the pump is switched off.
q ;
1.2 Air system
The 4 cylinders are supplied with air through 4 individual
induction pipes which are connected to one common inlet
duct. The pressure sensor and the vacuum advance for the
ignition distributor are also connected to the common
inlet duct.
There is a throttle valve, which is operated by a linkage
from the accelerator pedal, at the mouth of the common
inlet duct. Air is drawn into the common inlet duct through
an air filter.
When driving, the air flow into the common inlet duct is
controlled by the throttle valve. When idling, the throttle
valve is completely closed. The idling air enters the
common inlet duct only via a by-pass port behind the
throttle valve. The idling speed is set by altering the cross-
section of the by-pass pipe.
Jan, 1972
Adjustment of the idling speed should only take place when
the engine is warm, approx. 80° C (175° F) cooling liquid
temperature. This will ensure that the auxiliary air regulator
is closed. The engine not fully warmed up requires an
additional air flow for smooth running. This is controlled
by the auxiliary air regulator @. It alters the effective
cross-sectional area of the auxiliary air pipe depending
on the cooling liquid temperature.
The position of the regulator is dependent on an element
made of expanding material which projects into the cool-
ing liquid. At about —30° C (—22° F) the regulator is fully
open, and at about +60°C (140°F) it is completely
closed.
234-6
SAAB
Page 194
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1.3 Principles of operation
Key to schematic of system
Fuel tank
Fuel pump
Fuel filter
Pressure regulator
Pressure sensor
Common inlet duct
Cylinder head
Injection valves (fuel injectors)
Fuel distributor pipes to the 4 injectors
Ignition distributor with trigger contacts
Start valve
Throttle valve switch
Idling adjustment screw
Temperature sensor | (intake air)
Temperature sensor I (cooling liquid)
Auxiliary air regulator
Temperature switch
@ From starter terminal 50
©OOOOQOOQODOOOOOOO OOO
234-7
Information for the control unit
Information
Signal
A Pressure sensor
Load condition of the engine
B Trigger contacts Engine speed, triggering
of ignition distributor signal for start of injection
Cc Temperature sensor Il Warming up
(cooling liquid)
D+E Throttle valve switch Switching off the fuel supply
+N while coasting in gear, tem-
porary enrichment and for
2.0 | engine, supply fuel at
full throttle
F From starter termi- Start enrichment
nal 50 (if at the same
time temperature
switch is closed)
L Temperature sensor! Correction of injected quan-
(intake air) tity, dependent on air temper-
ature in the intake manifold
G To injection valves
H To fuel pump
M To start valve
J+K Cooling liquid circuit to the auxiliary air regulator.
Nov. 1972
Page 195
Due to the fuel pressure, fuel is injected during the time
for which the injector is open. The nozzle duct of the
fuel injector is accurately calibrated. Since the fuel pres-
sure is kept constant, the injected quantity of fuel is
dependent only upon the length of time for which the
injector is open.
The duration of injection is “computed” by the control
unit. The information processed by the electronic control
unit comes from the individual sensors on the engine. This
is done in the following manner:
The moment when the fuel is injected is controlled by the
distributor contacts (trigger contacts | and Il) according
to the position of the cam shaft (B). These contacts are
installed under the centrifugal advance mechanism in the
distributor and are maintenance-free.
The duration of injection (fuel quantity) is governed basi-
cally by two factors: by the engine speed and the load
condition of the engine. The engine speed is relayed to
the control unit by the distributor contacts | and II. The
load condition is determined by measuring the absolute
pressure in the inlet manifold. This pressure is converted
to an electrical impulse and relayed to the control unit
by the pressure sensor ©, which is connected to the
common inlet duct © by a hose (A).
The control unit processes this information and gives a
signal for the injectors to be open for a longer or shorter
period of time (G). The control unit thus allows a varying
amount of fuel to be passed through the electrically
operated injectors depending on engine load and speed.
This is how the “basic quantity” of fuel is governed.
In addition to the “basic quantity” of fuel, an accurately
metered amount of fuel is injected additionally when
starting at low ambient temperatures, when warming up,
during acceleration and at full load.
The start valve @ injects fuel into the common inlet duct
for as long as the starter is operated and at a cooling
liquid temperature of up to approximately 0+5°C
(+32 + 9°F) for 1.7 and 1.85 | engines and +5 + 5°C
(+41+9°F) for 2.0 l engines (closed temperature switch).
The additional quantity of fuel gives an considerably
better cold start performance of the engine.
The control unit receives the signal “warming up” (C)
from the temperature sensor | in the cooling liquid cir-
cuit H®.
The temperature sensor! @ (intake air) in the air filter
corrects the injected quantity dependent on air temper-
ature.
The throttle valve switch ® on 1.7 and 1.851 engines has
two functions. Firstly, it signals “coasting in gear’ (D)
(braking with the engine); in this condition no fuel
should be injected. This operating condition is charac-
terised by a closed throttle valve and increased engine
speed. The throttle valve switches off the fuel supply
when coasting in gear, at a speed over 1600 rev/min (for
2.0 | engine 1850 rev/min). If, when coasting in gear, the
speed drops to 1000 rev/min (for 2.0 | engine 1050 rev/
min), the fuel supply is switched on again so that a
smooth change-over to idling operation is guaranteed.
When the engine is cold, the speed limits are raised by
approx, 300 rev/min to equalize the higher frictional re-
sistance.
The second function of the throttle valve switch is to
give the control unit the information “more fuel” (E) when
the accelerator is depressed. This means that for tempo-
rary enrichment, a certain accurately metered quantity of
fuel is injected in addition to the normal amount of fuel.
On 2.0 | engine, the throttle valve switch has another
function (N). Its task is to give the engine a somewhat
richer fuel/air mixture at full throttle. This gives the en-
gine an improved inner cooling at extended periods of
high speed driving.
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Commencement
of injection
Ignition
firing point
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By signals from the control unit, the fuel injectors (8)
are opened electrically in two groups (group 1: cyl. 3
and 4; group 2: cyl. 1 and 2).
The two fuel injectors of one group inject at the same
time. The injectors of cylinders 1 and 4 inject fuel
during the expansion stroke and the injectors of cylinders
Nov. 1972
3
3 and 4 during the exhaust stroke. The injectors always
inject onto the still closed inlet valves and store the fuel
there. This fuel is transferred later, when the inlet valve
opens, together with the air stream into the combustion
chamber.
Page 196
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1.4 Electronic controls
Description
@® Electrically operated fuel pump
® Pressure sensor
@ Electro-magnetic injection valves
@ Ignition distributor with trigger contacts
@ Start valve
@® Throttle valve switch
@ Temperature sensor | {intake air)
@® Temperature sensor |! (cooling liquid)
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Temperature switch (cold start)
From starter terminal 50
Pump relay
Main relay
Electronic control unit
Fuse no. 8 in main fuse box
Terminal 15 (of series resistor of ignition coil)
Ground
Sept. 1973
Page 197
Description of the cable runs
Remark:
The individual cables are marked with the corresponding
cable number. These numbers are printed at a distance
of about %/, in from the plug.
Cable Cable
Number From To Number
1 control unit temperature 1
sensor |
(intake air)
2 not used
3 control unit injection valve 3
cyl. 4
4 control unit injection valve 4
cyl. 3
5 control unit injection valve 5
cyl. 4
6 control unit injection valve 6
cyl. 2
7 control unit pressure sensor M4
8 control unit pressure sensor 8
9 control unit throttle valve 9
switch
10 control unit pressure sensor 10
1 control unit ground ah
12 control unit ignition distributor 12
13 control unit temperature 13
sensor |
(intake air)
14 ~~ control unit throttle valve 14
switch
15 control unit pressure sensor 15
16 ~— control unit main relay 16
terminal 87
17 control unit throttle valve 17
switch
18 ~~ control unit starter 18
terminal 50
19 control unit pump relay 19
terminal 85
20 control unit throttle valve 20
switch
ignition distributor 21
(trigger contact)
21 control unit
ignition distributor 22
(trigger contact)
22 ~~ control unit
temperature 23
sensor II
(cooling liquid)
23 control unit
Nov, 1972
Cable Cable
Number From To Number
24 control unit main relay 24
terminal 87
25 ~— not used ground 25
26 fuel injector ground 26
cyl. 1
27 ‘fuel injector ground 27
cyl. 2
28 fuel injector ground 28
cyl. 3
29 fuel injector ground 29
cyl. 4
30 pump relay main relay 30
terminal 86 terminal 87
31 start valve starter 31
terminal 50
32 temperature ground 32
sensor
33 start valve temperature switch 33
34 main relay
terminal 30/51
battery + 34
When the ignition is switched on, the control unit @®
receives its operating voltage directly from the battery via
the main relay @. The fuel pump is controlled by the pump
relay ®. The pump relay only works either when the starter
is operated (terminal 50) or when the speed of the engine
is higher than 200 rev/min, This feature ensures that the
combustion chamber cannot become filled with fuel
should a fuel injector become defective.
A time switch installed in the electronic control unit allows
the fuel pump to run for approximately one second after
the ignition is switched on in order to build up the fuel
pressure at once.
234-10
Page 198
TESTING INSTRUMENT EFAW 228 S 12 WITH PRESSURE °””
GAUGE
2. Testing Instruments and
Tools Required
Tester EFAW 228 S 10 (839194) for testing the
system in the vehicle 0 681 500 001
Dwell-tach tester
Stroboscopic timing light
Vacuum tester
Tester trolley for carrying the testers,
e.g. EFAW 172A 0 681 169 084
Extractor hook for cable harness plug, to be made. Fig.5
3 clampers for closing off the fuel hoses; to be obtained
from Matra-Werke, D6 Frankfurt/Main, Dieselstr. 30, Part
No. W 157.
a = 45 mm (13/, in)
b = 12 mm (1% in)
c¢ = ca. 100 mm (approx. 3'4/14 in)
material: welding wire 2mm @ (eg in D)
3. Testing the Fuel Injection
System with Test Instrument
EFAW 228 S10
With the test instrument EFAW 228 S 10 all the sensors as
well as the fuel pump and the injectors are tested accord-
ing to the set program. It is important that all points be
checked.
All the steps described in the following must be carried
out with the ignition switched off!
Removing the control unit:
Remove the control unit (above the left wheelhouse) by
unscrewing the 3 fastening screws (arrows). Pull out the
control unit. Fig. 6
Open the cable clamp (arrow) with a Phillips screw driver
and push off the cover in the direction indicated by the
arrow. Fig.7
SAAB Dec. 1975
Page 199
Carefully pull the cable harness plug out of the control
unit with the extractor hook (to be made according to
fig. 5). Fig. 8
Connect the cable harness plug to the multiple plug on
the test instrument EFAW 228 S 10. Fig. 9
When refitting the control unit, observe the following:
Push the cable harness plug carefully into the control
unit (the plug can only be connected in one direction).
Carefully push the rubber grommet on the cable harness
into the recess on the control unit.
Put the cover and the cable clamp back in place. Refit
the control unit in its mounting above the wheelhouse
and fasten (see fig. 6).
Jan. 1971 Sine
234-12
Page 200
Preparatory work for the test (without electronic control unit connected):
Switch on ignition, turn switch “A” to position “Measuring”.
The test stages are listed in the following chart.
When checking the fuel injection system the entire test program must always be carried out.
Any defects which are found should be eliminated before testing is continued.
Position of switch B
Operate
to measure
Voltage | Switch on ignition and leave on Voltage supply for the control unit
throughout the following test proce-
dure
Voltage II
Voltage Operate starter for a short time Voltage at terminal 50 of starter
Starter
Adjustment “ co”, pressure sensor
234-13
Set test instrument to “co” by turning the adjustment knob
Push “ground” button
Resistance between pressure sensor
windings and ground (short circuit to
ground)
Push “primary” button
Resistance of primary windings of
pressure sensor
Push “secondary” button
Resistance of secondary windings of
pressure sensor
Jan. 1971