Chapter 6
Emissions control systems
6-23
*I Oxy en sensor
“2 Air-fPow sensor
“3 Intake air temperature sensor
*4 Engine coolant temperature sensor
“5 Throttle position switch
*6 Idle position switch
“7 Top dead center sensor
l 8 Crank angle sensor
*9 Barometric pressure sensor
l
ignition switch - ST
l
Ignition switch - IG,
l
Power supply
l
Vehicle-speed sensor,
l
Air conditioner switch
l
Power steering oil
pressure switch <A/T>
l
Inhibitor switch <AIT>
Canister
‘8
B
ON - OFF
*l Injector
*2 idle speed control servo
*3 Purge control solenoid valve
l
Fuel pump control (control. relay)
l
Air conditioner power relay
0 Ignition timing control
l
Self-diagnosis circuit
l
Malfunction indicator light
Fast idle air valve
speed control servo
solenoid valve
pressure sensor
From fuel pump -+
) To fuel tank
*7 Top dead center
sensor
sensor
Vacuum hose color
B: Black
L: Light blue
R: Red
Catalytic converter
14.1~ Multi-Poinflnjection (MPI) system (3.OL Federal and Canadian models)
32 At 68-degrees F, the resistance should be 2.45 K-ohms. At 176-de-
grees F (cool&t temperature), the resistance should be 296 ohms.
33 If the coolant temperature cannot be monitored closely, drain the
cooling system (see Chapter I), remove the sensor and heat the end in a
pan of water to the specified temperatures, then take the resistance read-
ings. If this is done, make sure the sensor body is at least l/8-inch away
from the water surface.
34 When reinstalling the sensor, use sealant on the threads and tighten it
to the torque listed in this Chapter’s Specifications.
Vacuum switch check
35 The vacuum switch is mounted on the right side of the firewall.
36 Unplug the wiring harness connector and attach the leads of an ohm-
meter or self-powered test light to the switch terminals. No continuity
should be indicated.
37 Disconnect the vacuum hose from the switch fitting and attach a
hand-held vacuum pump to the fitting with a section of hose.
38 Apply a vacuum of 10.2 in-Hg (?60 mm-Hg) or more and make sure
continuity is indicated. Release’the vacuum and verify that continuity is in-
terrupted.
\
39 If the switch fails the check, replace it with a neti one.
14 Multi-Point Injection (MPI) system
Refer to illustrations 14. la, 14. lb, 14. lc, 14. Id, 14.3a and 14.3b
1 A Multi-Point Injection (MPI) system is used on all 1990 and, later
models. MPI is a computerized engine management system which con-
trols all emission, fuel and ignition functions. The fuel control functions of
the MPI system are covered in Chapter 4. The information in this Section
concerns the electroniccontrol unit (ECU), the information sensors it uses
to monitor the MPI system and the emission devices it uses to adjust the
system (see illustrations).
2 The ECU is the “brain”of the MPI system. its sophisticata’d network of
information sensors monitor engine operation and transmit digital voltage
signals to the ECU. The ECU analyzes this data, compares it to the “map”
(program) stored in its memory and fine-tunes variables such as ignition
timing, spark advance, fuel injector pulse width and idle speed by read-
justing various devices such as the fuel injectors, the idle speed control
servo, the purge control solenoid valve, etc. The result is an always correct
air-fuel ratio under all driving conditions that lowers exhaust emissions
and maintains good driveability.
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