gas recirculation. The EGR operates during all
engine speed and load conditions. At wide open throt-
tle, it provides a 5% recirculation rate. The EGR
shuts down during high engine idle to avoid carbon
build up on the valve. The EGR also deactivates if
the EGR temperature is too high. The EGR also has
a self cleaning function that opens and closes twice
after the engine has been shut off to eliminate soot
deposits.

Apart from the charge air distribution manifold

and the mixing chamber, the intake manifold also
includes a finned EGR cooler. Coolant flows through
the cooler to reduce the temperature of the recircu-
lated gas after it was cooled by running through the
cylinder head. The management of this temperature
significantly reduces emissions (Fig. 1).

25 - 4

EXHAUST GAS RECIRCULATION

VALVE

DESCRIPTION

Exhaust gas recirculation reduces the quantity of

fresh air supplied to the cylinders per stroke without
having to throttle the air supply. Exhaust gas is
recirculated during all engine speed and engine load
conditions. As a result, emissions are reduced. If a
quantity of exhaust gas is mixed with the air that is
to be used to burn the fuel in the cylinders, the oxy-
gen content is reduced because the exhaust gas is
low in oxygen. The result is that the combustion rate
is reduced, as is the combustion temperature. This
reduces the quantity of NOx that are emitted in the
exhaust gas. (Fig. 2).

The ECM power supply relay has a power off delay

feature. The relay is powered off approximately 15
seconds after the ignition switch is turned off. This
allows for the self-cleaning function of the EGR valve
and a function check of the sensors for diagnosis pur-
poses.

Fig. 1 EGR AND COOLER

1 - EGR VALVE

3 - COOLING FINS

2 - COOLANT PASSAGE

4 - EXHAUST GAS PASSAGE

EXHAUST GAS RECIRCULATION

25 - 5

OPERATION

The mass of the air supplied to the cylinders per

stroke is the decisive factor for determining the opti-
mum quantity of exhaust gas for the operating con-
dition. This is calculated from the Mass Air Flow
sensor information.

The ECM evaluates this signal as well as that

from the Charge Air Pressure sensor, and outputs a
PWM signal in accordance with one of the maps
stored in it. The signal is sent to the exhaust gas
recirculation valve. The map is formulated to keep
the NOx as low as possible. The EGR valve is actu-
ated by an electric positioning motor and has a self
cleaning function. Every time the ignition switch is
turned off, the valve rotates twice to eliminate any
carbon deposits.

REMOVAL

NOTE: The EGR and EGR Cooler are serviced as an
assembly.

(1) Disconnect the negative battery cable.
(2) Partailly drain the cooling system (Refer to 7 -

COOLING/ENGINE/COOLANT - STANDARD PRO-
CEDURE).

(3) Lift up on the charge air hose retaining clip at

the intake manifold and disconnect hose with seal

(4) Disconnect the electrical connector at the EGR

positioner (Fig. 3).

(5) Disconnect the EGR cooler hose.
(6) Remove the EGR fasteners and EGR with

cooler assembly (Fig. 3).

INSTALLATION

(1) Clean all gasket mating surfaces.
(2) Position the EGR positioner to the intake man-

ifold with a new gasket, install bolts and tighten to
124 lbs.in (14 N·m) (Fig. 3).

(3) Connect the EGR positioner electrical connec-

tor (Fig. 3).

(4) Inspect the seal of the charge air inlet tube,

replace as necessary (Fig. 3).

(5) Seat the charge air tube with gasket into the

intake manifold and push down on the charge air
tube retaining clip.

(6) Refill the cooling system (Refer to 7 - COOL-

ING/ENGINE/COOLANT

STANDARD

PROCE-

DURE).

(7) Connect negative battery cable.

VALVE COOLER

DESCRIPTION

The exhaust gas recirculation (EGR) cooler is an

integrated part of the EGR valve. Coolant flows
around the exhaust gasses, cooling them before they
are remixed with the incoming air and reburned in
the combustion chamber (Fig. 4).

Fig. 2 EXHAUST GAS RECIRCULATION

1 - EGR VALVE
2 -CHARGE AIR PRESSURE SENSOR
3 - EXHAUST MANIFOLD
4 - EGR DUCT IN CYLINDER HEAD
5 - INTAKE MANIFOLD

Fig. 3 EGR VALVE

1 - EGR VALVE
2 - INTAKE MANIFOLD
3 - EGR COOLER HOSE
4 - HARNESS CONNECTOR

25 - 6

EXHAUST GAS RECIRCULATION

The EGR valve and Cooler are serviced as an

assembly, refer to (Refer to 25 - EMISSIONS CON-
TROL/EXHAUST GAS RECIRCULATION/VALVE -
REMOVAL).

Fig. 4 EGR AND COOLER

1 - EGR VALVE
2 - EGR COOLER
3 - INTAKE MANIFOLD

EXHAUST GAS RECIRCULATION

25 - 7

Content .. 358 359 360 361 ..