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are absorbed into the activated carbon (charcoal) storage
device (canister) in order to hold the vapors when the
vehicle is not operating. The canister is purged by PCM
control when the engine coolant temperature is over 60°C
(140°F), the IAT reading is over 10°C (50°F), and the
engine has been running. Air is drawn into the canister
through the air inlet grid. The air mixes with the vapor and
the mixture is drawn into the intake manifold.
EVAP Emission Control System Operation
The EVAP canister purge is controlled by a solenoid valve
that allows the manifold vacuum to purge the canister.
The powertrain control module (PCM) supplies a ground
to energize the solenoid valve (purge on). The EVAP
purge solenoid control is pulse-width modulated (PWM)
(turned on and off several times a second). The duty
cycle (pulse width) is determined by engine operating
conditions including load, throttle positron, coolant
temperature and ambient temperature. The duty cycle is
calculated by the PCM. The output is commanded when
the appropriate conditions have been met.
conditions are:
f The engine is fully warmed up.
f The engine has been running for a specified time.
f The IAT reading is above 10°C (50°F).
A continuous purge condition with no purge commanded
by the PCM will set a DTC P1441.
Poor idle, stalling and poor driveability can be caused by:
f A malfunctioning purge solenoid.
f A damaged canister.
f Hoses that are split, cracked, or not connected
properly.
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
These
Enhanced Evaporative Emission Control
System
The basic purpose of the Enhanced Evaporative
Emissions control system is the same as other EVAP
systems. A charcoal-filled canister captures and stores
gasoline fumes. When the PCM determines that the time
is right, it opens a purge valve which allows engine
vacuum to draw the fumes into the intake manifold.
The difference between this and other systems is that the
PCM monitors the vacuum and/or pressure in the system
to determine if there is any leakage. If the PCM
determines that the EVAP system is leaking or not
functioning properly, it sets a Diagnostic Trouble Code
(DTC) in the PCM memory.
The enhanced EVAP system is required to detect
evaporative fuel system leaks as small as 0.040 in. (1.0
mm) between the fuel filler cap and purge solenoid. The
system can test the evaporative system integrity by
applying a vacuum signal (ported or manifold) to the fuel
tank to create a small vacuum. The PCM then monitors
the ability of the system to maintain the vacuum. If the
vacuum remains for a specified period of time, there are
no evaporative leaks and a PASS report is sent to the
diagnostic executive. If there is a leak, the system either
will not achieve a vacuum, or a vacuum cannot be
maintained. Usually, a failure can only be detected after a
cold start with a trip of sufficient length and driving
conditions to run the needed tests. The enhanced EVAP
system diagnostic will conduct up to eight specific
sub-tests to detect fault conditions. If the diagnostic fails
a sub-test, the PCM will store a Diagnostic Trouble Code
(DTC) to indicate the type of detected.
6E–525
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