Exhaust Gas Recirculation (Egr) System; Egr Valve Solenoid; Location Of The Egr Valve On Four-Cylinder Models; Location Of The Egr Valve On Inline Six-Cylinder Models - Jeep cherokee 1989 Owner's Manual

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Exhaust Gas Recirculation (EGR) system

General description
1 High combustion temperatures raise the level of NOx (oxides of
nitrogen) emissions in the exhaust. The Exhaust Gas Recirculation (EGR)
system lowers NOx levels by allowing small amounts of exhaust gas
into the combustion chamber to reduce combustion temperature.
2 The principal component of all EGR systems used on vehicles
covered by this manual is the EGR valve itself. The EGR valve is a back-
pressure or vacuum controlled device which regulates the amount of
exhaust gas bled into the intake. The EGR valve is usually open during
warm engine operation and anytime the engine is running above idle
speed. The amount of gas recirculated is controlled by variations in
vacuum and exhaust backpressure.
3 The vacuum supply for the EGR valve is controlled by an EGR valve
solenoid which is in turn controlled by the Electronic Control Module
or ECU, the solenoid closes and prevents vacuum from reaching the
EGR valve. When it's not energized, the solenoid is open and vacuum
is applied to the EGR valve. The ECM or ECU monitors engine coolant
temperature and other operating conditions to determine when EGR
operation is desired.
4 On inline six-cylinder engines, a vacuum transducer is installed in-
line between the EGR valve solenoid and the EGR valve. The transducer
is controlled by exhaust backpressure. When backpressure exceeds
a preset value, the transducer allows vacuum to actuate the EGR valve.
5
Common engine problems associated with the EGR system are
rough idling, stalling at idle, rough engine performance during light
throttle application and stalling during deceleration.
Checking
Refer to illustrations 6.8a, 6.86, 6. 1 l a and 6.1 l b
EGR valve
6 Perform the EGR valve checking procedures in Chapter 1.
7 If the EGR valve appears to be in proper operating condition,
-
models when checking the valve, remove the vacuum
hose and connect a hand vacuum pump
The Motor Manual Guy
Chapter 6 Emissions and engine control systems
carefully check all hoses connected to the valve for cracks, leaks and
kinks. Replace or repair the valve and hoses as necessary.
8 With the engine idling at normal operating temperature, detach the
vacuum hose from the EGR valve and connect a vacuum pump. Note:
On four-cylinder and inline six-cylinder engines, the EGR valves are
located where shown (see illustrations). On V6 engines, the EGR valve
is located on the intake manifold, in front of the carburetor
body. If the EGR valve is operating properly, the engine should stumble
or stall when you apply vacuum. Replace the EGR valve with a new
one if the idle remains unchanged.
9 Because of the EGR system's interrelationship with the ECM or
ECU, further checks of the system are beyond the scope of the home
mechanic. Have the system checked by a dealer service department
or certified emission control repair shop.

EGR valve solenoid

1 0 Warm the engine up t o normal operating temperature.
11 With the engine idling, detach the vacuum hose at the solenoid
vacuum source (see illustrations) and attach a vacuum gauge to the
hose. Verify the vacuum is at least 15 in-Hg.
a) If vacuum is low, check the hose for kinks, twists or a loose con-
nection at the manifold fitting.
ceed to the next step.
12 Detach the hose at the solenoid output port and attach a vacuum
gauge to the port. The vacuum reading should be zero.
a) If the vacuum reading is zero, leave the gauge connected and
proceed to the next step.
a dealer service department (special tools are required for further
checking).
1 3 Detach the electrical connector at the solenoid and determine
whether there is vacuum at the solenoid output port. Vacuum should
now be present at the output port.
a) If vacuum is present, the EGR valve may be faulty. See the EGR
checking procedure above.
Location of the EGR valve on inline six-cylinder
-
models when checking the valve, detach the vacuum
-
hose (arrow) when removing the valve, detach the
transducer vacuum inlet hose
or throttle