6-10 Chapter 6 Emissions control systems
Sub EGR confrof valve
Therms valve
valve
Throttle valve
7.3a EGR system (49-state models) 7.3b EGR system (California models)
to EGR control valve
coolant temperature detection
7.3~ Therm0 valve (49-state models)
-~-.-. -“” ~_
7.4a Dual EGR control valve (California models)
6 Now start the engine and allow it to idle, then apply a vacuum of 4.3
in-Hg or more to the air control valve with the pump. Disconnect the hose
from the air cleaner and place your hand over the open end of the hose.
You should feel suction.
Replacement
7 Removal of the reed valve is very simple. Pull the rubber hose off the
inlet and unscrew the valve from the air pipe. Be sure to use a backup
wrench on the pipe so it doesn’t become twisted when the valve is un-
screwed.
8 Installation is the reverse of removal.
7 Exhaust Gas Recirculation (EGR) system
Description (carbureted models)
US
models
Refer to illustrations 7.3a, 7.3b, 7.3c, 7.4a, 7.4b, 7.5 and 7.6
1
Thevehiclescovered inthismanualutilizean ExhaustGas Recircula-
tion (EGR) system to reduce oxides of nitrogen in the exhaust.
2 The stringent oxides of nitrogen emission standards require high
rates of EGR flow, which adversely affects driveability of the vehicle. To
solve this problem, it is necessary to increase EGR flow during high load
vehicle operation and decrease EGR flow to improve driveability during
low load operation.
3 To accomplish this, two different systems are in use; one for vehicles
sold in California and one for vehicles sold in the remaining 49 states (see
illustrations).
Both systems utilize an EGR control valve, a sub-EGR
control valve and a thermal valve
(see illustration).
4 The California system has a dual EGR control valve (primary and sec-
ondary), which is controlled by different carburetorvacuums in respon,se
to throttle valve openings
(see illustration).
The primary EGR valve con-
trols EGR flow during relatively narrow throttle valve openings, while the
secondary EGR valve takes over as the throttle valve is opened wider.
EGR flow is suspended completely at idle and wide open throttle condi-
tions. The thermal valve
(see illustration),
which senses coolant temper-
ature, controls the vacuum applied to the EGR control valve.
to purge control valve
to secondarv EGR
closed at above 55’ C (131” F)
b closed at above 35” C (95” F)
/ -_--- -- - / ---- ---
_---_-.I lJ.-.--LT.-
’ Therm0 sensor for
coolant temperature defectron
7.4b
Therm0 valve (California models)
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