Chapter 18 Diagnosis and Repair of the Emission Control and Exhaust Systems 395
Copyright by Goodheart-Willcox Co., Inc.
of the manifold studs. If the diaphragm can be serviced,
separate it from the valve assembly. If only the diaphragm
is being replaced, make sure that the valve moves freely.
Loosen it with penetrating oil and light hammer tapping if
needed. Reassemble the valve and diaphragm as necessary
and reinstall the assembly on the engine. Be sure to check
operation after the new parts are installed.
Thermal Vacuum Valve
To replace the thermal vacuum valve, depressurize
and drain the cooling system to a level below the switch.
Use a box-end wrench or socket to remove the switch.
Specialized sockets are available to remove these switches.
Compare the old and new switches. Coat the threads of
the new switch with the correct type of sealant and install
the switch in the coolant passage. Recheck operation after
installing the switch.
EGR Valve
The EGR valve is usually mounted on the top or side
of the engine. Refer to Figure 18-34. Start by removing
the electrical and vacuum connections. Then, remove the
bolts holding the valve to the intake manifold. If the EGR
bolts are diffi cult to turn, spray the bolts with penetrating
oil before continuing removal. Finally, pull the valve from
the engine.
Check the assembly for carbon deposits that may be
holding the valve open. Some EGR valves can be cleaned
and reused by striking the pintle with a soft-faced hammer
to knock loose any accumulated deposits, Figure 18-35.
Be careful not to damage the valve during this operation.
Also check the ports in the intake and exhaust manifolds for
excessive carbon buildup and clean if necessary.
If the valve has a non-integral position sensor, remove
the attaching screws and separate the sensor from the valve
body. Assemble the sensor on the new valve body using a
new gasket.
Before reinstalling the valve, check the EGR passages
for carbon buildup and clean them as necessary. Place a
new gasket over the EGR opening, then reinstall the EGR
valve and attaching screws. Reattach the vacuum hose
and electrical connector. After reinstalling the EGR valve,
recheck the operation of the system.
EGR solenoids cannot be repaired. They are replaced
as a unit. To replace the solenoid, disconnect the electrical
connectors and vacuum lines. Then, remove the fasteners
holding the solenoid to the bracket. Compare the new and
old solenoid assemblies to ensure that they are correct.
Then, install the new solenoid. Recheck EGR operation
after the solenoid is installed.
Note: On a few systems, the EGR solenoid
is part of the EGR valve and diaphragm
assembly. If the solenoid is defective, the
entire valve assembly must be replaced.
Air Injection System
The air injection system is comprised of the air-injec-
tion pump, drive belt, diverter valve(s), check valves, and
associated hoses and piping. Most of these parts are easily
removed. The valves and hoses can be removed by loosen-
ing the hoses and any attaching hardware. The fi ttings for
the exhaust system check valve and manifold tubing often
corrode at the exhaust manifold. If they are hard to remove,
soak them with penetrating oil and use a fl are-nut or box-
end wrench to loosen the threads. Always use new gaskets
where applicable for reinstallation.
Check valves commonly fail before other parts of
the air injection system. Begin removal of the check
valve by detaching the hose. Then, remove the old check
Figure 18-34. EGR valves are normally bolted directly to the
intake manifold or plenum. Some are remotely mounted close to
the engine and use a bolt-on pipe or passage.
Figure 18-35. If an EGR valve must be reused, it can be cleaned.
If the pintle is sticking, clean the valve and tap lightly on the base
with a soft-faced hammer. (Subaru)
Soft-faced hammer