Page 151
Fuel Injection
some other system such as the ignition system, consult 200
Engine-General first.
1. Check the intake (induction) system for leaks. Check for
cracked, loose, or disconnected hoses and duct work.
Check that all hose clamps are tight. On Turbo cars, be
sure to check the hoses and hose clamps at the turbocharger by-pass valve. See 291 Turbocharger.
NOTE
An air leak allows unmeasured air to enter the engine, often
resulting in an in overly lean fuel mixture and causing driveability problems.
2. Check that the battery is in good condition. Check that
the battery cables are tight and free of corrosion. Check
that all related ground points are firmly connected and
in good condition. Don't forget to check the main
ground at the battery. Check all of the harness connectors for damage and corrosion. Check for power and
ground at the LH control unit. See 371 Wiring Diagrams, Fuses and Relays.
3. Check the fuses.
4. Check for sufficient fuel in the tank. If the engine ran out
of fuel it takes up to two gallons to prime the pump. See
234 Fuel Pump and Fuel Tank.
5. Check for spark at the spark plugs. If the tachometer
needle bounces while the engine is cranked by the
starter then the ignition system is probably working correctly. See 340 Ignition System.
240-5
NOTE
• As a general rule, a steady-on Check Engine light means the
LH control unit has detected a fault. A flashing Check Engine
light means that the ElK Ignition system has detected a fault.
As an exception to the rule, the check engine light on 1992
models does not flash. Therefore, a steady-on Check Engine
light on these models could be either an ElK system or an LH
system fault.
• LH 2.2 is not equipped with LH on-board diagnostics. Although these models are equipped with a check engine light,
it is primarily used for ElK ignition system fault detection. On
LH 2.2, the Check Engine light will come on in the event of an
air mass meter fault and the engine will go into a "limp-home"
mode.
The fault code display is triggered by grounding a pin at the
LH control unit test connector. A special Saab test harness
(tool no. 83 93 886), available from an authorized Saab dealer, should be used to make the test. As an alternative, a
switched test lead can be constructed using simple electrical
components. Be sure to make the lead long enough to reach
the driver's seat.
The following on-board diagnostic codes are broken into
two parts-one for LH faults and the other for component and
signal testing.
To display LH fault codes
1. With the ignition key off and the test lead switch off,
connect one end of the lead to ground and the other
end to the connector terminal shown in Fig. 3.
1988
1989 on
6. On cars with LH 2.4 and LH 2.4.2, check for any faults
through the on-board diagnostics system (LH 2.4 and
LH 2.4.2 only) as described below.
On-board Diagnostics
(LH 2.4 and LH 2.4.2 only)
LH 2.4 and LH 2.4.2 fuel injection systems feature built-in
diagnostic circuitry that detects and stores coded fault information in the LH control unit's memory. When the system
compensates for values that are outside the permitted limits, a
fault code is generated. The fault codes can be "read-out"
through the Check Engine light.
The system has the ability to store up to three fault codes,
including intermittent faults. The system also has a built-in test
cycle that can actively test all major fuel injection components
and their signals.
875361
Fig. 3. Switch lead shown connected to test connector. On 1988
models the 3-pin connector is in the engine compartment,
near the fresh air intake. On 1989 and later sedan models the
1O-pin connector IS beneath the rear seat. On 1989 and later
convertible models, the 10-pin connector IS under the bellows ahead of the shifter.
FAUL T DIAGNOSIS
Page 152
240-6
Fuel Injection
CAUTION
Carry out the tests exactly as shown. An extra few seconds at
the wrong time can clear the fault memory.
2. With the engine off and the test lead switch OFF, turn
the ignition key to the ON position.
3. When the Check Engine light comes on, turn the test
lead switch ON. The light should immediately go out.
4. Wait until the Check Engine light flashes once and then
immediately turn the test lead switch OFF.
5. A fault code (if present) will begin to flash through the
Check Engine light. There is a long flash at the beginning and end of each code. The code itself is a series
of short flashes. Once the code is fully displayed it will
begin to repeat itself until the next code is called up. Table b lists fault codes, their probable faults, and corrective actions.
Table b. Fuel Injection On-board Diagnostic Fault Codes (LH 2.4, LH 2.4.2 only)
Error code
Check Engine light in
normal driving
Probable fault
Corrective action, first check
12231
Off
No rpm signal (this code will always be
present if the test is run with the engine
off). Crank the engine for 5 seconds. If the
code disappears, the rpm signal is O.K.
Check fuse no. 3. Check the ignition
system input at pin 1 of the LH control unit
12221
On
No signal from airmass meter(LH system
is in limp-home mode)
Check air mass meter connections.
Check for airmass meter bum-off. (Do not
interchange air mass meter from LH 2.2component damage may result)
12214
On
Coolant temperature signal incorrect
(temperature signal out of range: below 90°C or above 160°C)
Test coolant temperature sensor. Make
resistance test at pin 13 of LH control unit
and ground. (Resistance should be
approx. 2280-2720 ohms at 68°F (20°C)
and 290-365 ohms at 176°F (80°C))
12211
Off
Incorrect battery voltage (below 10 volts
or over 16 volts with engine running)
Check charging system, battery
connections, grounds, etc.
12225
On
Incorrect oxygen sensor output. Sensor
pre-heater circuit may be open. (Engine
temp. must be above 176°F for 1988
model, or above 158°F for 1989 and later
model)
Check oxygen sensor output voltage
(voltage fluctuating between 0 and 1.0
volt). Check oxygen sensor pre-heater
circuit and fuse
12223
On
Air-fuel mixture too lean
12241
On
Air-fuel mixture fault
12224
On
Air-fuel mixture too rich
Tighten all boot clamps and carefully
check all hose connections. Check
injector a-rings. Check ELCD
valve. Check fuel pressure. (Also see fault
code 12225 above)
12233
On
LH control unit fault (ROM mixture fault)
Replace LH control unit
12242
On
Air mass meter bum-off function fault
-
Check air mass meter wiring and bum-off
function
I
12243
Off
No signal from road speed sensor
Check signal output from road speed
sensoron speedometer. Check for power
and ground supply at sensor
12244
Off
AfT "Drive" signal faulty. (signal absent
while driving or constantly present even
when stopped)
Check the fuse for the reverse lights, the
reverse light switch, the wiring
connections, etc
12245
On
EGR temperature too low (where
applicable)
Check function of EGR system. See 254
Exhaust Emission Control
12232
Off
Memory voltage below 1 volt
Check for battery voltage at pin 4 of the
LH control unit with the ignition off
12212
Off
Idle contacts in throttle position switch
shorted, closed throttle switch while
driving (LH 2.4 only)
Check and adjust throttle position switch.
Check wiring harness for short to ground
I
._
continued on next page
FAULT DIAGNOSIS
Page 153
Fuel Injection
240-7
Table b. Fuel Injection On-board Diagnostic Fault Codes (LH 2.4, LH 2.4.2 only) (continued)
Error code
Check Engine light in
normal driving
Corrective action, first check
Probable fault
f-----------+---------+----------------+-.-------------------
12251
Off
Incorrect or missing signal from throttle
potentiometer (LH 2.4.2 only)
12213
Off
Full throttle contacts in throttle position
switch shorted, full throttle signal at idle
(LH 2.4 only)
Off
I__
I
Check and adjust throttle position switch.
Check wiring hamess for short to ground
Check electrical connections between LH
control unit and AIC valve
problem (incorrect air-fuel ratio while
O_ff
_1_2_11_1
Check throttle potentiometer function
(hamess disconnected at potentiometer)
sensor pre-heater circuit and sensor
+_odriving)
__x_y_g_e_n_s_en_s_o__r_s_el_f-_c_om_p_en_sa_ti_ng_Ci_rC_U_it-t_C_h_e_C_k_fo_r_a_i
r_f_ue_I_le_a_k_S_'
C_h_e_c_k_th_e_o_xy_ge_n------j
output. Check
ELCD system.
Check fuel
pressures
1-
12112
Off
Oxygen sensor self-compensating circuit
problem (incorrect air-fuel ratio at idle)
12113
Off
AIC self-compensating circuit problem
(system unable to reduce idle speed to
Check throttle stop screw setting. Check
throttle plate for an over-center condition.
Check for vacuum leaks
12114
Off
AIC self-compensating fault. (system
unable to increase idle to an acceptable
level)
Check for binding AIC valve. Check for a
mechanical engine problem causing low
idle problem
No more faults
No corrective action necessary. This code
must be present before fault memory can
be erased
I
I
Off
00000
!
_~o rrect leveIL _
j
i
I
NOTE
NOTE
As an example, if the test is run with the engine off, the first
code displayed would be for "no RPM signal" (fault code 1-22-3-1), This would be viewed as a long flash followed by a single flash, two flashes, two flashes, three flashes, and ending
with a single flash. The light would then come one for a long
flash and the code would begin to repeat itself. See Fig. 4.
After making repairs, it takes a certain amount of time for the
LH system to re-adapt or compensate for the new conditions.
Usually ten minutes of driving, allowing the engine to reach
operating temperature, should be sufficient. Recheck for the
"no more faults" code only after making a test drive to prevent
the same error codes from reoccurring.
ICI>rt&9>eID1 DD
DD
DDD
D1 Ic"'* &9>e1I
2
2
3
~opStaIt
Sto¢bt
1. With the engine off, the test lead switch OFF, and no
faults codes present as described above, turn the ignition key to the on position.
I
89140
Fig. 4.
I
2. As soon as the Check Engine light comes on, turn the
test lead switch ON. The light should immediately go out.
Graphic representation of flashing Check Engine light.
6. To cycle to the next fault code, simply turn the test lead
switch ON, wait until the Check Engine light flashes
once, and then turn the switch OFF. Any new codes will
begin to flash.
NOTE
The test sequence can be restarted by allowing the Check Engine light to flash twice before tuming the switch OFF. Do not
let the light flash three times, as this can cancel the fault memory.
3. Wait until the Check Engine light flashes three times
and then turn the test lead switch OFF. The fault memory will now be erased.
To test components and signals
The LH 2.4 and LH 2.4.2 control unit has a built-in component test that actively tests all major fuel injection components. The test will also display a code through the Check
Engine light.
1. On cars with automatic transmission, place the transmission in "0".
To erase fault code memory
Before erasing the memory, the error code 00000 ("no more
faults") listed in Table b must be present.
FAUL T DIAGNOSIS
Page 154
240-8
Fuel Injection
2. With the ignition key off and the test lead switch off,
connect the switched test lead as shown above in Fig. 3.
the pressure regulator, and 2) Residual pressure-the pressure maintained in the closed system after the engine (and
fuel pump) are shut off.
3. Turn the test lead switch ON.
4. Turn the ignition key ON and wait for a short flash of the
Check Engine light, then immediately turn the test lead
switch OFF.
NOTE
As soon as the check engine light flashes, the fuel pump
should run briefly (provided the pump is functioning correctly).
This is the first component tested, verifying that the component and signal diagnosis program has been accessed. The
Check Engine light will not flash a test code during the fuel
pump test.
5. To move on to the next component test (and test code),
Relieving Fuel Pressure and Connecting
Fuel Pressure Gauge
Much of the work on fuel injection requires the disconnecting of fuel lines. To prevent fuel from spraying all over, especially on a hot engine, it is a good idea to relieve the pressure
in the lines before fully disconnecting them.
One basic method of relieving the pressure is to remove the
fuses for the fuel pump and then run the engine until it stalls.
Another method is to connect a hand vacuum pump to the
vacuum connection on the fuel pressure regulator. When vacuum is applied to the regulator it will open and dump fuel back
to the tank.
turn the test lead switch on. After a short flash, turn the
switch OFF. The fuel injectors should be clicking on and
off.
6. Proceed through the remaining tests using the same
procedure of turning the test lead switch on, waiting for
a short flash and turning the switch OFF. Table c lists
the test sequence, the test code, the signal or component being tested, and the operational check being
made.
FUEL PRESSURE TESTS
WARNING
Fuel will be discharged during many fuel system tests described below. Do not smoke or work near heaters or other fire
hazards. Have a fire extinguisher handy.
Basic system troubleshooting requires a pressure gauge to
measure fuel pressure under different operating conditions.
To install the pressure gauge, remove the banjo bolt holding
the fuel supply line to the fuel rail. See Fig. 5. Then reinstall the
supply line and the gauge fitting.
Checking the fuel pressure is a fundamental part of troubleshooting and diagnosing the system. An accurate fuel pressure gauge will be needed to make the tests described below.
There are two significant fuel pressure values: 1) System
pressure-created by the main fuel pump and maintained by
NOTE
Use Saab pressure gauge Part No. 83 93 852, or an equivalent that has a range of at least 0 to 5 bar (approximately 0 to
100 psi). Always use new sealing washers when making connections.
Table c. Fuel Injection Component Test (LH 2.4, LH 2.4.2 only)
Test sequence
Test Code
Component/signal being checked
Operational check
No light display
Fuel pump circuit
Listen for pump running or fuel flow in the engine
compartment
12411
Injector circuit
3
12412
AIC actuator circuit
4
12413
1
I,
I
I
2
~
I
Listen for clicking injectors
f-----------
f----
5
I
12421
~~I
AIC valve will audibly cycle between open and
closed once a second
ELCD (charcoal canister purge valve)
I
ELCD valve audibly clicks once a second
Automatic transmission drive position signal
Flashing stops when shifting from drive to
neutral
r-Closed throttle signal from throttle position
Flashing stops when throttle is opened
~-
6
12424
7
12431
~h
Full throttle signal from throttle position switch
I
FUEL PRESSURE TESTS
Flashing stops as accelerator pedal approaches
I full
.
throttle
Page 155
Fuel Injection
240-9
Fuel jPPIY line
Spring
in from
Fuel rail
----
Fig. 5.
87537
Fuel pressure gauge installation location at fuel supply line on
front of fuel rail.
CAUTION
Absolute cleanliness is essential when working with fuel circuit components. Even a minute particle of dirt can cause
trouble if it reaches an injector. Thoroughly clean the unions
before disconnecting any fuel lines. Use clean tools.
Fuel Pressure Regulator
The fuel pressure regulator is mounted to the end of the fuel
rail and is spring operated. See Fig.6 and Fig. 7. Fuel pump
pressure presses on the regulator valve diaphragm. The
valve opens at a set pressure and returns excess fuel to the
tank. When the pump shuts off, the regulator valve closes,
holding residual pressure in the fuel system. This helps prevent fuel vaporization in the lines and possible vapor lock.
The pressure regulator is connected to the intake manifold
through a vacuum hose. As manifold pressure changes, it
t
Retum to
fuel tank
87571
Fig. 7. Cutaway view of LH fuel pressure regulator.
acts on the pressure regulator diaphragm to increase or decrease fuel pressure in the same ratio. Thus the pressure differential between fuel pressure in the system and manifold
pressure is constant. This ensures that the amount of fuel injected is influenced only by injector opening time, and not by
intake manifold pressure.
Checking System Line Pressure
System pressure is checked in two steps. The first step
checks basic operation of the pressure regulator. The second
step checks the regulator's response to manifold pressure.
With the fuel gauge connected as described above and the
engine off, run the fuel pump by bypassing the fuel pump relay
as described in 234 Fuel Pump and Fuel Tank. System pressure specifications are given in Table d.
Table d. System Pressure - Fuel Pump
Running, Engine Off
Fuel Pressure
Model
f--.
I
Non-Turbo models
3.0 bar (43.5 psi)
--
Turbo models
I
25±.05 bar (36.3±0.7 psi)
I
Vacuum
hose
I.
Fig. 6.
Fuel return
line
87550-S2I306
NOTE
Pressure specifications give fuel pressure relative to normal
atmospheric pressure (1 bar/14.5 psi) in the intake manifold.
Fuel pressure regulator.
FUEL PRESSURE TESTS
Page 156
240-10
Fuel Injection
If system pressure is too high, first check for a blocked or
damaged fuel return line from the pressure regulator. Also
check the return line check valve. If there are no obstructions,
replace the pressure regulator.
NOTE
The fuel retum line check valve is either near the fuel tank or
in the top of the fuel tank depending on the type of tank installed. See 234 Fuel Pump and Fuel Tank.
If system pressure is too low, first check for fuel leaks. Test
the fuel pump as described in 234 Fuel Pump and Fuel Tank.
A restricted fuel 'filter or a damaged fuel line are also potential
causes. If there are no other faults, replace the pressure regulator.
To check pressure regulator response to manifold pressure, reinstall the fuel pump fuse and then start the engine.
With the engine idling, system pressure should be slightly lower than with the engine off. See Table e. If not, check the regulator vacuum hose and its connection to the intake manifold.
If there are no faults, the regulator is faulty and should be replaced.
Table e. System Pressure -
Engine Idling
Model
Fuel Pressure
Non-Turbo models
2.4 bar (34.8 psi)
Turbo models
1.9 bar (27.6 psi)
Table f. Residual Pressure
All models
0.1-0.2 bar (1.5-3 psi) below
system pressure, maximum
after 10 minutes
are no leaks, then either the pressure regulator or the fuel
pump check valve is faulty.
To determine which, turn the pump on and off again, then
immediately clamp shut the fuel return line at the pressure
regulator. If pressure still drops, then the fuel pump check
valve is faulty. See 234 Fuel Pump and Fuel Tank for replacement. If residual pressure is now OK, then the pressure
regulator is faulty.
Checking Fuel Pump Delivery Pressure
The fuel pump is capable of developing a much higher pressure than that regulated by the pressure regulator. The fuel
pump has an internal check-valve that will not allow the system pressure to exceed 6.0 bar (87 psi).
To check fuel pump delivery pressure, run the fuel pump
with the engine off. Then briefly pinch shut the return line at
the pressure regulator. The fuel pressure should quickly rise.
If the pressure does not respond quickly, and no leaks can be
found, the fuel pump is worn and should be replaced.
CAUTION
NOTE
• These pressures are approximate, and based on a manifold
pressure of -0.6 bar (-8.7 psi) at idle. Allowances should be
made for altitude and other factors influencing manifold pressure.
• The most accurate test of pressure regulator response is
made by using a hand vacuum pump and pressure pump
(Turbo models) to apply vacuum/pressure to the regulator
with the fuel pump running. Fuel pressure should always be
lesser/greater than system pressure by the same amount of
vacuum/pressure that is applied.
In the event the fuel pump check valve is faulty (stuck closed),
make sure the fuel pressure does not rise above 6.0 bar (87
psi). Damage to the fuel lines or fuel system components
could result.
NOTE
Additional fuel pump tests, including testing the fuel pump relay, are covered in 234 Fuel Pump and Fuel Tank.
ELECTRICAL CHECKS AND
COMPONENT TESTING
Checking Residual Pressure
Hot-start problems are usually the only reason to suspect a
residual pressure problem, but it deserves a routine check as
long as the gauge is connected.
With the engine off, run the fuel pump for about 30 seconds
or so to pressurize the system. Turn the pump off and watch
the pressure gauge. Table f gives the specification.
If pressure drops beyond specification, check for leaks in
the fuel lines, at the fuel pump, and at the fuel injectors. If there
ELECTRICAL CHECKS AND COMPONENT TESTING
Before making any electrical checks or tests, disconnect
the main harness connector from the LH control unit and from
the air mass meter. The control unit is behind the side kick
panel in the front passenger compartment. See Fig. 8. When
making tests at harness connectors, probe from the rear of the
connector only, as the small delicate pins in the connector can
be easily spread apart, causing faUlty or intermittent signals.
Peel back rubber boots and remove seals to gain access to
the rear of the connector.
Page 157
Fuel Injection
240-11
CAUTION
CAUTION
• Avoid damaging hamess connectors or relay panel sockets.
Jumper wires should end with flat-blade connectors that are
the same size as the connector or relay terminals.
On models with LH 2.4 and LH 2.4.2, always wait at least 40
seconds after tuming off the ignition before removing the control unit connector. If the connector is removed before this
time, residual power in the system relay may damage the control unit.
• Always switch a meter to the appropriate function and range
before making test connections.
• Connect and disconnect test equipment only with the ignition switched off.
System relay
I~
3. Connect pin 21 in the LH control unit connector to
ground. Turn the ignition key on and check for voltage
at pin 9 of the LH control unit connector. See Fig. 9.
Check for voltage at the air mass meter connector; on
cars with LH 2.2 check for voltage at pin 2 and on LH
2.4 and LH 2.4.2, check for voltage at pin 5.
NOTE
If no faults are found, the system relay is working correctly. If
the voltage is not as specified, continue testing as described
below.
(GRNT)
\ I
\
87585
Fig. 8.
LH control unit (arrow) behind kick panel in passenger compartment ahead of front door.
(GRNT)
System Relay
The system relay supplies power to the LH control unit and
the fuel pump relay when the ignition key is in the run position.
On later models with LH 2.4, the system relay also supplies
power to the fuel injectors, the air mass meter, the AIC idle
valve, and the charcoal canister purge valve (ELCD). If this relay is faulty the engine will not start.
87595
Fig. 9.
To test system relay
Voltage being measured at air mass meter connector (pin 2
on LH 2.2 or pin 5 on LH 2.4 and LH 2.4 .2) and LH control
unit connector (pin 9).
1. With the ignition key off, remove the harness connector
from the air mass meter and the LH control unit.
2. Working at the LH control unit connector, check for
ground at pin 11 on LH 2.2 or at pin 17 on LH 2.4 and
LH 2.4.2. Repair any wiring faults using the appropriate
wiring diagram shown in 371 Wiring Diagrams, Fuses
4. Remove the system relay and check for voltage at terminal 30 and terminal 86 of the relay socket. See Fig.
10. If any faults are found, check the wiring between
the battery and the relay sockets using the appropriate
wiring diagram.
and Relays.
ELECTRICAL CHECKS AND COMPONENT TESTING
Page 158
240-12
Fuel Injection
87
851
878 186
30
I
•
I
I
I
I
I
I----..-..A-- J
I
L
87661
-------------------'
Fig. 10. Voltage being checked at system relay terminals 30 and 86.
5. If voltage is as specified in step 3, check the wiring between the system relay sockets and the following components; the LH control unit connector (pin 21 and pin
9), the air mass meter connector (pin 2 on LH 2.2 or pin
5 on all others), and the fuel pump relay (terminal 86).
If no wiring faults can be found, the system relay is
probably faulty.
NOTE
On 1985 through 1988 tUrbo models, a turbo over-pressure
switch interrupts power to the fuel pump relay (terminal 86)
when the turbocharger's boost pressure gets too high. Check
for continuity in the wire between terminal 87 of the system relay socket and terminal 86 of the fuel pump relay socket. If
there is no continuity, test the turbo over-pressure switch as
described in 234 Fuel Pump and Fuel Tank.
Fig. 11. Coolant temperature sensor.
NOTE
A faulty coolant temperature sensor will cause a noticeable increase in idle speed, as well as possibly affecting driveability.
On LH 2.4 and LH 2.4.2 the Check Engine light should illuminate.
Table g. Coolant Temperature Sensor Resistance
Temperature
c
-4 F (-20"C)
I 14,000
14°F (-WC)
9,000
32°F (OCC)
5,8))
!D'F (10°C)
3,800
&F(15"C)
3,000
68°F (20°C)
2,600
76°F (25"C)
2,000
86°F (30°C)
1,700
176°F (80°C)
320
--
Coolant Temperature Sensor
The coolant temperature sensor sends continuous engine
temperature information to the LH control unit. If there is break
in the signal from the temperature sensor, the ECU will simulate a fixed signal, and the system will continue to operate
based on an engine temperature of 68°F (20°C) on cars with
LH 2.2 or 113°F (45°C) on cars with LH 2.4 and LH 2.4.2.
The sensor is mounted in the intake manifold. See Fig. 11.
It projects into the cylinder head to measure engine coolant
temperature. The sensor has a negative temperature coefficient (NTC), which means that its resistance goes down as its
temperature goes up.
To check the sensor, disconnect the harness connector
and check the resistance across the sensor terminals. Table
9 lists sensor resistances based on engine temperature. If
any faults are found, the sensor should be replaced as described later under Component Replacement.
ELECTRICAL CHECKS AND COMPONENT TESTING
Resistance (ohms, ±10%)
Throttle Position Sensor
The throttle position sensor is mounted on the side of the
throttle housing and is directly connected to the throttle valve
shaft. See Fig. 12. The sensor provides a signal to the control
unit based on the position of the throttle valve.
On models with LH 2.2 and LH 2.4 fuel injection, there are
two switches in the housing that provide a ground signal
whenever the throttle is fully closed or fully open.
Page 159
Fuel Injection
240-13
On models with LH 2.4.2 fuel injection, there is a potentiometer in the housing that changes resistance as the throttle
moves. The control unit sends a voltage signal to the position
sensor and monitors the voltage that comes back. Resistance
decreases (voltage increases) as the throttle opens.
87664
I
Fig. 13. Throttle position sensor being checked on cars with LH 2,2
and LH 2.4,
87663-82/308
----~----
Fig. 12. Throttle position sensor (arrow) mounted to side of throttle
housing,
Check throttle position sensor function by disconnecting the
harness connector and checking continuity across the terminals while changing the throttle position. See Fig. 13. Table h
and Table i list the correct test results. If the results are incorrect, check sensor adjustment as described below under LH
Fuel Injection Adjustments. If adjustment does not correct
the problem, replace the throttle position sensor.
Table i. Throttle Position Sensor Tests-LH 2.4.2
Throttle position
Terminals checked
i
Test results
closed
1 and 3
~2600-3000 ohm,-
wide open
1 and 3
i
1100-1500 ohms
between closed
and wide open
1 and 3
continuously
variable between
1100--3000 ohms,
with no dropouts
Air Mass Meter
NOTE
On models with LH 2.4.2, the throttle potentiometer is non-adjustable. If test results are incorrect, replace the throttle position sensor,
The heart of the LH fuel injection system is the air mass
meter. It is located between the air filter and the intake manifold. The air mass meter electronically measures the air entering the engine. The air mass meter has no moving parts.
Table h. Throttle Position Sensor Tests-LH 2.2
and LH 2.4
When the engine is running, a current is used to heat a thin
wire in the center of the meter. See Fig. 14. The current flowing through the wire is regulated to maintain a wire temperature that is always 100°C more than that of the cooler air
passing over it. The current used to heat the wire is then electronically converted into a precise voltage measurement corresponding to the air entering the engine.
Throttle position
Terminals checked
Test results
closed
1 and 2
continuity
2 and 3
no continuity
1 and 2
no continuity
2 and 3
no continuity
1 and 2
no continuity
2 and 3
continuity
-
-
half open
wide open
-
Because the hot wire measures air mass, no other inputs to
the control unit are needed for air temperature or altitude. A
screen across the meter intake helps protect the wire and also
breaks up air flow for more accurate measurements. To keep
the wire free from dirt, it is heated to a temperature of about
1000°C (1830°F) for one second. This "burn-off" cycle takes
place automatically, four seconds after the engine is turned off.
If the hot wire breaks or if there is no output from the air
mass meter, the control unit automatically switches to a "Iimphome" mode and turns on the Check Engine light. The engine
ELECTRICAL CHECKS AND COMPONENT TESTING
Page 160
240-14
Fuel Injection
87666
Fig. 15. Voltmeter connected to air mass meter terminals 1 (-) and 4
(+) to check for meter burn-off voltage.
87665-821327
Fig. 14. Air mass meter.
can usually be started and driven. The air mass meter has no
internal moving parts and cannot be serviced.
6. Start and rev the engine to at least 2500 rpm, then shut
it off. After about 4 seconds, the voltage should rise to
about 4 volts for a duration of one second. If the voltage
is as specified, but the wire does not glow as described
in step 3 above, the air mass meter is faulty and should
be replaced.
To test air mass meter
1. Disconnect the air mass meter from the air cleaner
only. Leave it connected to the duct leading to the intake manifold and leave the wiring harness connected.
NOTE
• On models with LH 2.2, a new replacement air mass meter
should be adjusted as described below under LH Fuellnjection Adjustments. Air mass meters used on LH 2.4 and 2.4.2
do not require any adjustments.
2. Start engine and run it to normal operating temperature
3. Rev the engine to at least 2500 rpm, then shut it off.
Look through the front of the meter at the hot wire. After
approximately four seconds the wire should glow
brightly for about one second.
NOTE
If the wire glows as specified, then the air mass meter and
control unit are probably operating correctly. If the wire does
not glow, continue testing.
4. Remove the air mass meter and look through it to see
if the wire is broken. It's very small, so check carefully.
If the wire is broken, the meter will have to be replaced
as described below. If the wire is intact, continue testing.
5. Reinstall the air mass meter and the harness connector. Peel back the rubber boot 'from the harness connector. Working 'from the rear of the connector, connect
a digital voltmeter across terminals 1 and 4. See Fig. 15.
CAUTION
Use only a digital voltmeter for the above test. An analog
meter can damage the air mass meter.
ELECTRICAL CHECKS AND COMPONENT TESTING
• The air mass meter used on LH 2.2 (aluminum body) is not
the same meter used on LH 2.4 and LH 2.4.2 (black plastic
body). Do not interchange these meters.
7. If voltage is not present in step 6, turn the ignition key
on and check for voltage and ground at the meter's
connector. There should be ground at pin 4. There
shou Id be positive (+) battery voltage at pin 2 (LH 2.2)
or at pin 5 (LH 2.2, LH2.4.2).
If any faults are found, check for wiring breaks between the
air mass meter and the LH control unit and between the air
mass meter and the system relay. Also check the operation of
the system relay as described above.
Fuel Injectors
The fuel injectors are electrically operated solenoid valves.
They are switched on and off (open and closed) by the LH
control unit. The injectors are connected to a common fuel
supply, called the fuel rail. See Fig. 16.
There are a couple of common injector problems. Carbon
deposits that form at the tips of injectors will clog them and reduce fuel flow. This often causes rough running, stalling, and
power loss. This problem can usually be reduced and controlled through the use of quality gasolines containing deter-