4-18 DRIVEABILITY AND EMISSIONS CONTROLS
- From under the drivers seat, unbolt the ECM from the leg.
- Carefully disengage the 3 harnesses form the ECM.
To install: - Attach the harnesses to the ECM. Secure to the seat leg with i
mounting bolts. - Connect the negative battery cable. Reset any electronic devi
as the radio, clock, etc.
Oxygen Sensor
OPERATIONis suchThe exhaust oxygen sensor or 02S, is mounted in the exhaust stfbam
where it monitors oxygen content in the exhaust gas. The oxygen cc itent in
the exhaust is a measure of the air/fuel mixture going into the engin!. The
oxygen in the exhaust reacts with the oxygen sensor to produce a village
which is read by the ECM.
There are two types of oxygen sensors used in these vehicles. They!are the
single wire oxygen sensor (02S) and the heated oxygen sensor (H02S'
oxygen sensor is a spark plug shaped device that is screwed into the e
pipes. It monitors the oxygen content of the exhaust gases and sends;
signal to the Electronic Control Module (ECM). The ECM monitors thi
and, depending on the value of the received signal, issues a command
mixture control solenoid on the carburetor to adjust for rich or lean coi
The heated oxygen sensor has a heating element incorporated in
sensor to aid in the warm up to the proper operating temperature an
The
(haust
voltage
voltage
to the
ditions.
othe
Jto
maintain tiat temperature.
The proper operation of the oxygen sensor depends upon four ba^ic
conditions:- Good electrical connections. Since the sensor generates low dlirrents,
good clean electrical connections at the sensor are a must. - Outside air supply. Air must circulate to the internal portion o the
sensor. When servicing the sensor, do not restrict the air passages. - Proper operating temperatures. The ECM will not recognize th| sen-
sor's signals until the sensor reaches approximately 600°F (316°C),
Non-leaded fuel. The use of leaded gasoline will damage the 3
TESTINGensor** WARNING
Do not pierce the wires when testing this sensor; this can
to wiring harness damage. Backprobe the connector to pr
read the voltage of the H02S.Single Wire Sensor- Start the engine and bring it to normal operating temperaturf
run the engine above 1200 rpm for two minutes. - Backprobe with a high impedance averaging voltmeter (set h
voltage scale) between the oxygen sensor (02S) and battery ground - Verify that the 02S voltage fluctuates rapidly between 0.40-0.6
- l': the 02S voltage is stabilized at the middle of the specified
(approximately 0.45-0.55 volts) or if the 02S voltage fluctuates ver
between the specified range (02S signal crosses 0.5 volts less than
lead
perlythenthe DCvolts,
ange
slowly
5 times
in ten seconds), the 02S may be faulty.- If the 02S voltage stabilizes at either end of the specified ranjhe, the
ECM is probably not able to compensate for a mechanical problem ;uch as
a vacuum leak or a faulty pressure regulator. These types of mechan cal
problems will cause the 02S to sense a constant lean or constant ri|:h mix-
ture. The mechanical problem will first have to be repaired and thenythe 02S
test repeated. - Pull a vacuum hose located after the throttle plate. Voltage s
drop to approximately 0.12 volts (while still fluctuating rapidly). Thi
the ability of the 02S to detect a lean mixture condition. Reattach th>
uum hose.
ould
; tests
vac-- Richen the mixture using a propane enrichment tool. Voltage should
rise to approximately 0.90 volts (while still fluctuating rapidly). This tests
the ability of the 02S to detect a rich mixture condition. - If the 02S voltage is above or below the specified range, the 02S
and/or the 02S wiring may be faulty. Check the wiring for any breaks, repair
as necessary and repeat the test.
Heated Oxygen Sensor
I See Figure 49- Start the engine and bring it to normal operating temperature,
then run the engine above 1200 rpm for two minutes. - Turn the ignition OFF disengage the H02S harness connector.
- Connect a test light between harness terminals +B and HI With the
ignition switch ON and the engine off, verify that the test light is lit. If the test
light is not lit, either the supply voltage to the H02S heater or the ground cir-
cuit of the H02S heater is faulty. Check the H02S wiring and the fuse. - Next, connect a high impedance ohmmeter between the H02S ter-
minals of the heating element and verify that the resistance is 11.0-16.0
ohms at 68° F (20° C). - If the H02S heater resistance is not as specified, the H02S may
be faulty. - Start the engine and bring it to normal operating temperature,
then run the engine above 1200 rpm for two minutes. - Backprobe with a high impedance averaging voltmeter (set to the DC
voltage scale) between the oxygen sensor (02S) signal wire and battery
ground. - Verify that the 02S voltage fluctuates rapidly between 0.40-0.60 volts.
- If the 02S voltage is stabilized at the middle of the specified
range (approximately 0.45-0.55 volts) or if the 02S voltage fluctuates
very slowly between the specified range (02S signal crosses 0.5 volts
less than 5 times in ten seconds), the 02S may be faulty. - If the 02S voltage stabilizes at either end of the specified range, the ECM
is probably not able to compensate for a mechanical problem such as a vacuum
leak or a faulty fuel pressure regulator. These types of mechanical problems will
cause the 02S to sense a constant lean or constant rich mixture. The mechanical
problem will first have to be repaired and then the 02S test repeated. - Pull a vacuum hose located after the throttle plate. Voltage should drop
to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability
of the 02S to detect a lean mixture condition. Reattach the vacuum hose. - Richen the mixture using a propane enrichment tool. Voltage
should rise to approximately 0.90 volts (while still fluctuating rapidly).
This tests the ability of the 02S to detect a rich mixture condition. - If the 02S voltage is above or below the specified range, the 02S
and/or the 02S wiring may be faulty. Check the wiring for any breaks,
repair as necessary and repeat the test.
Ohmmeter
Fig. 49 Using an ohmmeter, measure the resistance between
the terminals of the oxygen sensor