Isuzu engine C22NE / 22LE / 20LE. Manual - part 118

DRIVEABILITY AND EMISSIONS  6E1-301

A/C CLUTCH DIAGNOSIS

A/C CLUTCH CIRCUIT OPERATION

A 12-volt signal is supplied to the A/C request input of the ECM
when the A/C is selected through the A/C control switch.
The A/C compressor clutch relay is controlled through the
ECM. This allows the ECM 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 ECM will enable the
A/C compressor relay. This is done by providing a ground path
for the A/C relay coil within the ECM. When the A/C
compressor relay is enabled, battery voltage is supplied to the
compressor relay is enabled, battery voltage is supplied to the
compressor clutch coil.
The ECM will enable the A/C compressor clutch whenever the
engine is running and the A/C has been requested. The ECM
will not enable the A/C compressor clutch if any of the following
conditions are met:
• The engine speed is greater than 6000 RPM.
• The ECT is greater than 122°C (251°F).
• The throttle is more than 95% open.

A/C CLUTCH CIRCUIT PURPOSE

The A/C compressor operation is controlled by the engine
control module (ECM) for the following reasons:
• It improves idle quality during compressor clutch

engagement.

• It improves 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 switch.
• The A/C refrigerant pressure switches.
• The A/C compressor clutch.
• The A/C compressor clutch relay.
• The ECM.

A/C REQUEST SIGNAL

This signal tells the ECM when the A/C mode is selected at the
A/C control switch. The ECM uses this input 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 ECM.
Refer to A/C Clutch Circuit Diagnosis for A/C wiring diagrams
and diagnosis for the A/C electrical system.

6E1-302  DRIVEABILITY AND EMISSIONS

EVAPORATIVE EMISSION (EVAP)
SYSTEM (IF APPLICABLE)

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 ECM 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
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 engine
control module (ECM) 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 position,
coolant temperature and ambient temperature. The duty cycle
is calculated by the ECM. 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 ECM will set a DTC 62.

• Purge/Vacuum Hoses. Made of rubber compounds, these

hoses route the gasoline fumes from their sources to the

canister and from the canister to the intake air flow.

• EVAP Canister. Mounted on a bracket ahead of the fuel

tank, the canister stores fuel vapors until the ECM

determined that engine conditions are right for them to be

removed and burned.

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.

DRIVEABILITY AND EMISSIONS  6E1-303

SYSTEM FAULT DETECTION

The EVAP leak detection strategy is based on applying
vacuum to the EVAP system and monitoring vacuum decay. At
an appropriate time, the EVAP purge solenoid is turned  "ON,"
allowing the engine vacuum to draw a small vacuum on the
entire evaporative emission system.
After the desired vacuum level has been achieved, the EVAP
purge solenoid is turned  "OFF,"  sealing the system. A leak is
detected by monitoring for a decrease in vacuum level over a
given time period, all other variables remaining constant.
If the desired vacuum level cannot be achieved in the test
described above, a large leak or a faulty EVAP purge control
solenoid valve is indicated.
Leaks can be caused by the following conditions:
• Missing or faulty fuel cap
• Disconnected, damaged, pinched, or blocked EVAP purge

line

• Disconnected, damaged, pinched, or blocked fuel tank vapor

line

• Disconnected or faulty EVAP purge control solenoid valve
• Open ignition feed circuit to the purge solenoid
• Damaged EVAP canister
• Leaking fuel sender assembly O-ring
• Leaking fuel tank or fuel filler neck
The ECM supplies a ground to energize the purge control
solenoid valve (purge  "ON" ). The EVAP purge control is
PWM, or turned  "ON"  and  "OFF,"  several times a second.
The duty cycle (pulse width) is determined by engine operating
conditions including load, throttle position, coolant temperature
and ambient temperature. The duty cycle is calculated by the
ECM and the output is commanded when the appropriate
conditions have been met.
The system checks for conditions that cause the EVAP system
to purge continuously by commanding the EVAP purge
solenoid  "OFF", EVAP purge PWM  "0%". If fuel tank vacuum
level increases during the test, a continuous purge flow
condition is indicated. This can be caused by the following
conditions:
• EVAP purge solenoid leaking
• EVAP purge and engine vacuum lines switched at the EVAP

purge control solenoid valve

• EVAP purge control solenoid valve driver circuit grounded

6E1-304  DRIVEABILITY AND EMISSIONS

POSITIVE CRANKCASE
VENTILATION (PCV) SYSTEM

CRANKCASE VENTILATION SYSTEM PURPOSE

The crankcase ventilation system is used to consume
crankcase vapors in the combustion process instead of venting
them to the atmosphere. Fresh air from the throttle body is
supplied to the crankcase and mixed with blow-by gases. This
mixture is then passed through the positive crankcase
ventilation (PCV) port into the intake manifold.
While the engine is running, exhaust gases and small amounts
of the fuel/air mixture escape past the piston rings and enter
the crankcase. these gases are mixed with clean air entering
through a tube from the air intake duct.

During normal, part-throttle operation, the system is designed
to allow crankcase gases to flow through the PCV hose into the
intake manifold to be consumed by normal combustion.
A plugged positive crankcase ventilation port or PCV hose may
cause the following conditions:
• Rough idle.
• Stalling or slow idle speed.
• Oil leaks.
• Sludge in the engine.
A leaking PCV hose would cause:
• Rough idle.
• Stalling.
• High idle speed.