Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 885

6E–564

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

between the seats. In extreme cases, exhaust blow-by
and damage beyond simple gap wear may occur.
Cracked or broken insulators may be the result of
improper installation, damage during spark plug
re-gapping, or heat shock to the insulator material. Upper
insulators can be broken when a poorly fitting tool is used
during installation or removal, when the spark plug is hit
from the outside, or is dropped on a hard surface. Cracks
in the upper insulator may be inside the shell and not
visible. Also, the breakage may not cause problems until
oil or moisture penetrates the crack later.

TS23994

A/C Clutch Diagnosis

A/C Clutch Circuit Operation

A 12-volt signal is supplied to the A/C request input of the
PCM when the A/C is selected through the A/C control
switch.
The A/C compressor clutch relay is controlled through the
PCM. This allows the PCM to modify the idle air control
position prior to the A/C clutch engagement for better idle
quality. If the engine operating conditions are within their
specified calibrated acceptable ranges, the PCM will
enable the A/C compressor relay. This is done by
providing a ground path for the A/C relay coil within the
PCM. When the A/C compressor relay is enabled,
battery voltage is supplied to the compressor clutch coil.
The PCM will enable the A/C compressor clutch
whenever the engine is running and the A/C has been
requested. The PCM will not enable the A/C compressor
clutch if any of the following conditions are met:

The throttle is greater than 90%.

The engine speed is greater than 6315 RPM.

The ECT is greater than 119

C (246

F).

The IAT is less than 5

C (41

F).

The throttle is more than 80% open.

A/C Clutch Circuit Purpose

The A/C compressor operation is controlled by the
powertrain control module (PCM) for the following
reasons:

It improvises idle quality during compressor clutch
engagement.

It improvises wide open throttle (WOT) performance.

It provides A/C compressor protection from operation
with incorrect refrigerant pressures.

The A/C electrical system consists of the following
components:

The A/C control head.

The A/C refrigerant pressure switches.

The A/C compressor clutch.

The A/C compressor clutch relay.

The PCM.

A/C Request Signal

This signal tells the PCM when the A/C mode is selected
at the A/C control head. The PCM uses this to adjust the
idle speed before turning on the A/C clutch. The A/C
compressor will be inoperative if this signal is not
available to the PCM.
Refer to

A/C Clutch Circuit Diagnosis section for A/C

wiring diagrams and diagnosis for A/C electrical system.

6E–565

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

General Description (Evaporative
(EVAP) Emission System)

EVAP Emission Control System Purpose

The basic evaporative emission (EVAP) control system
used on all vehicles is the charcoal canister storage
method. Gasoline vapors from the fuel tank flow into the
canister through the inlet labeled “TANK.” These vapors
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

(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. These
conditions are:

The engine is fully warmed up.

The engine has been running for a specified time.

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:

A malfunctioning purge solenoid.

A damaged canister.

Hoses that are split, cracked, or not connected
properly.

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–566

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

060R200214

Legend

(1) Vent Solenoid
(2) EVAP Purge Solenoid
(3) Throttle Body
(4) Fuel Filler Neck
(5) Fuel Tank
(6) Rollover Valve
(7) EVAP Canister
(8) Ignition Feed
(9) Ignition Feed

(10) EVAP Purge Solenoid Driver Signal from PCM

(11) Vent Solenoid Driver Signal from PCM

(12) Vent Filter
(13) Fuel Tank Pressure Sensor
(14) Fuel Tank Pressure Signal to PCM
(15) 5 Volt Reference “A” Circuit from PCM
(16) Sensor Ground Circuit from PCM
(17) Fuel Level Sensor
(18) Fuel Level Signal to PCM
(19) 5 Volt Return

Electrical Components
The electrical components that make up the enhanced
EVAP system are:

Fuel Tank Pressure Sensor. The fuel tank pressure
sensor is a three-wire strain gauge sensor similar to a
common MAP sensor. However, the fuel tank
pressure sensor has very different electrical
characteristics due to its pressure differential design.
The sensor measures the difference between the air
pressure (or vacuum) in the fuel tank and the outside
air pressure.

The sensor mounts at the top of the fuel pump
assembly. A three-wire electrical harness connects it to
the PCM. The PCM supplies a five-volt reference

voltage and a ground to the sensor. The sensor will
return a voltage between 0.1 and 4.9 volts. When the
air pressure in the fuel tank is equal to the outside air
pressure, such as when the fuel cap is removed, the
output voltage of the sensor will be 1.3 to 1.7 volts.
When the air pressure in the fuel tank is 4.5 in. H2O
(1.25 kPa), the sensor output voltage will be 0.5

0.2 V.

When there is neither vacuum nor pressure in the fuel
tank, the sensor voltage will be 1.5 V. At –14 in. H2O
(–3.75 kPa), the sensor voltage will be 4.5

0.2 V.

6E–567

TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS

EVAP Canister Purge Solenoid. Normally closed, the
purge solenoid opens upon the PCM’s signal to allow
engine vacuum to purge gasoline fumes from the
canister. Mounted on the water pipe to front of the
engine assembly.

060R200201

EVAP Canister Vent Solenoid. Located next to the
canister, the vent solenoid opens to allow air into the
EVAP system. Fresh air is necessary to completely
remove gasoline fumes from the canister during
purge. The EVAP vent solenoid closes to seal off the
evaporative emissions system for leak testing.

014RW148

Fuel Level Sensor. The fuel level sensor is an
important input to the PCM for the enhanced EVAP
system diagnostic. The PCM needs fuel level
information to know the volume of fuel in the tank.
The fuel level affects the rate of change of air
pressure in the EVAP system. Several of the
enhanced EVAP system diagnostic sub-tests are
dependent upon correct fuel level information. The
diagnostic will not run when the tank is less than 15%
or more than 85% full. Be sure to diagnose any Fuel
Level Sensor DTCs first, as they can cause other
DTCs to set.

060R200215

Manifold Absolute Pressure (MAP) Sensor. The
PCM compares the signals from the fuel tank
pressure sensor and the MAP sensor to ensure that a
relative vacuum is maintained the EVAP system.

055RW004

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