Isuzu 2000 Trooper UX, Руководство по ремонту

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6E–62
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
D
For the 3.5L w/automatic transmission, the
pre-catalyst sensor are designated Bank 1 HO2S 1
and Bank 2 HO2S 1. The post-catalyst sensors are
Bank 1 HO2S 2 and Bank 2 HO2S 2.
Catalyst Monitor Outputs
The catalyst monitor diagnostic is sensitive to the
following conditions:
D
Exhaust leaks
D
HO2S contamination
D
Alternate fuels
Exhaust system leaks may cause the following:
D
Preventing a degraded catalyst from failing the
diagnostic.
D
Causing a false failure for a normally functioning
catalyst.
D
Preventing the diagnostic from running.
Some of the contaminants that may be encountered are
phosphorus, lead, silica, and sulfur. The presence of
these contaminants will prevent the TWC diagnostic from
functioning properly.
Three-Way Catalyst Oxygen Storage Capacity
The Three-Way catalyst (TWC) must be monitored for
efficiency. To accomplish this, the control module
monitors the pre-catalyst HO2S and post-catalyst HO2S
oxygen sensors. When the TWC is operating properly,
the post-catalyst oxygen sensor will have significantly
less activity than the pre-catalyst oxygen sensor. The
TWC stores and releases oxygen as needed during its
normal reduction and oxidation process. The control
module will calculate the oxygen storage capacity using
the difference between the pre-catalyst and post catalyst
oxygen sensor’s voltage levels. If the activity of the
post-catalyst oxygen sensor approaches that of the
pre-catalyst oxygen sensor, the catalyst’s efficiency is
degraded.
Stepped or staged testing level allow the control module
to statistically filter test information. This prevents falsely
passing or falsely failing the oxygen storage capacity test.
The calculations performed by the on-board diagnostic
system are very complex. For this reason, post catalyst
oxygen sensor activity should not be used to determine
oxygen storage capacity unless directed by the service
manual.
Two stages are used to monitor catalyst efficiency.
Failure of the first stage will indicate that the catalyst
requires further testing to determine catalyst efficiency.
The seconds stage then looks at the inputs for the pre and
post catalyst HO2S sensors more closely before
determining if the catalyst is indeed degraded. This
further statistical processing is done to increase the
accuracy of oxygen storage capacity type monitoring.
Failing the first (stage 1) test DOES NOT indicate a failed
catalyst. The catalyst may be marginal or the fuel sulfur
content could be very high.
Aftermarket HO2S characteristics may be different from
the original equipment manufacturer sensor. This may
lead to a false pass or a false fail of the catalyst monitor
diagnostic. Similarly, if an aftermarket catalyst does not
contain the same amount of cerium as the original part,
the correlation between oxygen storage and conversion
efficiency may be altered enough to set a false DTC.
Evaporative Emission (EVAP) Purge
System Vacuum Switch
The EVAP system uses a switch located in the purge line
between the canister and the purge valve to detect when
purge is occurring. This switch senses the flow from the
engine through the purge valve. When no purge is
present, the switch is closed, applying a 12 volt signal to
the control module as a NO PURGE signal. When
canister purging occurs, the switch opens, interrupting
the 12 volt signal to the control module. A Tech 2 display
will indicate that purge is occurring.
Clogging of the canister fresh air vent could allow the
purge hose between the switch and canister to trap
vacuum with the purge valve closed. This would result in
a diagnostic indication of a purge valve stuck open or a
vacuum switch failure. Similarly, leaks or blockages in the
purge hoses may result in misdiagnosis of the purge valve
or vacuum switch.
When servicing a purge valve diagnostic trouble code,
check the canister fresh air vent, vacuum switch and the
integrity of all purge hoses prior to servicing the valve.
(Refer to EVAP Vacuum Switch in On-Vehicle Service
Procedures in this section.)
Misfire Monitor Diagnostic Operation
Misfire Monitor Diagnostic Operation
Misfire is monitored as a function of the combustion
quality (CQ) signals generated from the ignition current
sense system. Combustion signals represent the degree
of combustion in each cylinder. Misfire is detected when
the combustion signal is below a predetermined value.
The misfire ratio is calculated once every 100 engine
cycles. For example, on a 6-cylinder engine, 600 ignition
plug sparks occur every 100 cycles and if a misfire occurs
12 times during that time, the misfire is 12/600
×
100 = 2
%.
Misfire Counters
Whenever a cylinder misfires, the misfire diagnostic
counts the misfire and notes the crankshaft position at the
time the misfire occurred. These “misfire counters” are
basically a file on each engine cylinder. A current and a
history misfire counter are maintained for each cylinder.
The misfire current counters (Misfire Cur #1-6) indicate
the number of firing events out of the last 100 cylinder
firing events which were misfires. The misfire current
counter will display real time data without a misfire DTC
stored. The misfire history counters (Misfire Hist #1-6)
indicate the total number of cylinder firing events which
were misfires. The misfire history counters will display 0
until the misfire diagnostic has failed and a DTC P0300 is
set. Once the misfire DTC P0300 is set, the misfire