388 Auto Engine Performance and Driveability
Copyright by Goodheart-Willcox Co., Inc.
areas if necessary. Smoke should be visible at the leak
point. After correcting the leak, use the smoke machine to
retest the system.
Checking EGR Valves
Vacuum-operated EGR valves can be checked by
observing the valve stem or feeling for diaphragm move-
ment as the engine is accelerated, Figure 18-20. With the
transmission/transaxle in park or neutral, set the parking
brake. Have someone depress the brake pedal and then
accelerate the engine. This test can also be performed with
a portable vacuum pump. As the engine speed or vacuum
increases, the valve stem should move. If it does not, the
valve is stuck, the hose is leaking or plugged, or the vacuum
diaphragm is leaking.
Some vacuum-operated EGR valves will not work if
there is no backpressure. Have an assistant slightly restrict
the exhaust with a shop towel or other object. Then, per-
form the test.
To check the EGR pintle itself, the valve must be
removed from the engine. The valve and passages can then
be observed for sticking or excess buildup of deposits.
Note: If the EGR valve is controlled by a
solenoid, this test may not give accurate
results. Consult the service information for
exact testing procedures.
Diagnosing EGR Control Solenoids
A common cause of problems on vacuum-operated
EGR valves is a defective control solenoid. This solenoid con-
trols vacuum fl ow to the diaphragm based on an electrical
signal from the ECM. Most EGR control solenoids are nor-
mally open, allowing vacuum to the diaphragm when the
ECM does not signal the solenoid to close. Therefore, most
problems related to the solenoid result in the EGR valve
opening when it should not. This leads to hesitation, surging,
and stalling.
Some EGR control solenoids can be checked by
energizing them with jumper wires from the battery,
Figure 18-21A. A vacuum gauge and test light can be used
to check other EGR solenoids.
In Figure 18-21B, the EGR diaphragm is activated using
a vacuum pump. For the vehicle on which this EGR valve
is used, if the EGR diaphragm moves when the ignition is
on and the shift lever is in park, either the EGR solenoid or
ECM is defective. To check further on this vehicle, remove
the input wire from the EGR solenoid and attach a test light
to the solenoid terminals. If the light comes on with the
transmission in park, the solenoid is receiving a close signal
Figure 18-20. Feel the EGR diaphragm for movement as the
engine is accelerated. Be careful, as the EGR valve gets very
hot.
Figure 18-21. A—Some EGR solenoids can be checked by
jumping battery power to the terminals. Check the service infor-
mation before performing this test. B—A vacuum pump should
be used to simulate engine vacuum to the EGR valve. (Subaru)
EGR
solenoid
A
BATTERY
B