Isuzu N-Series. Manual - part 425

6E-36 EMISSION AND ELECTRICAL DIAGNOSIS

Governor (Model RLD-M)

The RLD-J type governor can be used with the MI,
MITICS injection pumps, and was designed to have bet-
ter control and endurance than the previous RLD type
governor.
Although the basic construction is identical to that of the
RLD type governor, the RLD-M type is larger to match
the applicable pumps’ larger size.

Features

Variable speed control governor with decreased le-
ver reaction force
As with the previous RLD type governor, RLD-M gover-
nor control is accomplished using the speed control le-
ver to change the fulcrum of the internal link mechanism.
Consequently, as the reaction force of the governor
spring does not act directly on the speed control lever,
only a very small lever reaction force is exerted on the
accelerator pedal.

Set torque characteristics through internal torque
cam
At full load, the tip of the sensor lever traces the face of
the torque cam to determine the full load rack position
and control the full load injection quantity.
Consequently, the torque characteristics demanded by
the engine can be freely set by changing the shape of
the torque cam face.

Improved control through internal guide plate
When the speed control lever is operated, the 2nd sup-
porting lever’s pin moves along the guide plate. The
floating lever connected to the pin thus moves to change
the ball joint fulcrum positions.
In the intermediate to high speed ranges, the guide plate
causes the floating lever to move to increase the lever
ratio continuously from 1.1 (idling) — 6 (full speed). This
increase in the lever ratio in the intermediate to high
speed range improves speed droop.

Legend

1. At maximum speed control
2. At idle speed control
3. Link mechanism
4. Speed control lever
5. Governor spring

N6A1147E

Legend

1. Sensor lever
2. Torque cam
3. Control rack position (mm)
4. Pump speed (r/min)

N6A1148E

N6A1149E

EMISSION AND ELECTRICAL DIAGNOSIS 6E-37

Timing Advance Control
Timing advance control is measuring the ECT to calcu-
late drive current of the solenoid switch for the injection
timing advance.
The injection timing is controlled by according to the
ECT when engine is started.
Solenoid Switch
The solenoid switch is installed on the top of the injec-
tion pump to push the advance lever in the injection
pump when 12 or 24 volts is supplied.
In this condition the injection timing is an additional.
10 degree (BTDC) from normal injection timing.
If there is some trouble for electricity current, it will set
the DTC-P23 or P24.
Refer to the DTC chart.
If remove the solenoid switch, it can not be reinstalled
because it is necessary to readjust advance value on
the injection pump tester.

EGR (Exhaust Gas Recirculation) System

EGR Purpose

The exhaust gas recirculation (EGR) system is use to
reduce emission levels of the oxides of nitrogen (NOx).
The NOx emission levels are caused by a high combus-
tion temperature. The EGR system lowers the NOx
emission levels by decreasing the combustion tempera-
ture.

EGR Control

The main element of the system is the EGR valve.
The EGR valve feeds small amounts of the exhaust gas
back into the intake manifold.
The EGR valve is controlled by the ECM and the ECM
uses information from the following sensors to control
the EGR valve.

• Engine coolant temperature (ECT) sensor.
• Engine speed sensor.
• Rack sensor
• Exhaust brake switch condition.
• Atmospheric pressure sensor.

EGR Valve Operation and Results of Incorrect
Operation

The EGR valve is designed to accurately supply EGR to
the engine independent of he intake manifold.
The EGR valve controls EGR flow from the exhaust
manifold to the intake manifold through the VSV (Vacu-

Legend

1. Ball joint
2. Floating lever
3. 2nd supporting lever pin
4. Guide plate
5. Speed control lever

Legend

1. Adjust screw for maximum advance angle
2. Adjust screw for minimum advance angle
3. Counter weight
4. Timing rod center
5. Return spring
6. Solenoid switch

N6A1150E

Legend

1. Advance angle
2. Pump speed
3. Minimum advance angle
4. Maximum advance angle
5. Advance angle by solenoid switch
6. Control character by flyweight

N6A1151E

6E-38 EMISSION AND ELECTRICAL DIAGNOSIS

um Switching Valve) with a ECM controlled EVRV (Elec-
tronic Vacuum Regulating Valve).
The ECM monitors related sensor or switch condition, if
EVRV solenoid has incorrect operation, DTC P31 or
P32 will be set.
If DTCs P13, P14, P21, P22,P35, P36, P45 or P61 are
set, refer to the DTC charts.

Rack Sensor

The rack sensor is engaged with tip of injection pump
rack.
The rack sensor signal will send during vehicle operat-
ing to the ECM, the ECM calculate together with other
sensor’s signal, the ECM output activation signal for
EVRV.

Atmospheric Pressure Sensor

The atmospheric pressure censor is built-in the ECM.
The EVRV activity will be stopped, when the atmospher-
ic pressure will comes below the setting pressure.

Exhaust Brake Switch

The exhaust brake switch is equipped on the steering
column.
The exhaust brake switch is controlled by vehicle oper-
ator, when during the vehicle operating the vehicle oper-
ator will demand to apply the exhaust brake for assist
the main brake system.

EGR Quick Cut Control

During the VSV action, when the EVRV drive current will
comes over the setting valve (the drive current will de-
cide relation of the engine load and speed) immediate
stop the VSV.
Result of this action will reduce the PM (Particulate Mat-
er). 

EVRV Control

The EGR is controlled under normal temperature with
separate stage by the ECT of engine condition.
ECM refer to EGR action map to demand the EVRV
drive current, also ECM controls agree EVRV drive cur-
rent and EVRV actual drive current each other.
Otherwise the ECM transitional stage controls for cur-
rent of EVRV when EGR is controlled moving OFF area
to ON area on the EGR action map.
Also stop the EVRV drive for stop the EGR system un-
der following conditions.
When under low temperature of the ECT.
When acting the QWS system.
When acting the exhaust brake
When the atmospheric pressure comes under setting
the pressure valve.

EMISSION AND ELECTRICAL DIAGNOSIS 6E-39

VSS (Variable Swirl System)

The Variable Swirl System (VSS) is designed to adjust the intensity of swirl by allowing or not allowing air to flow
through a sub-port (or bypass) the runs in parallel with the intake port for each cylinder. The swirl intensifies when
there is no air flow through the sub-port, and vice versa.
The air flow is controlled by the on-off valve at the inlet to the sub-port and the valve in turn is turned on and off by
computer signals which are dependent on engine speed, load and coolant temperature. Basically, the air is cut off at
low speeds to maintain high swirl and is allowed to flow at high speeds to maintain low swirl.

Variable Swirl System (Equipped with EGR and VSS)

Legend

1. Cylinder head

7. Engine speed sensor

2. VSS case

8. Rack sensor

3. Inlet port

9. VSV; VSS

4. Sub-port

10. Actuator

5. Vacuum

11. Control valve

6. Thermo sensor

12. Inlet manifold

N6A1152E