Chapter
D
: Emission Control Systems Diagnosis and Repair
74
3. Listen for a hissing noise from the valve.
4. Place a finger over the end of valve. A strong vacu-
um should be felt and engine speed should drop by
40 RPM or more if the system is working properly.
If engine speed does not increase when the valve is dis-
connected, or does not drop at least 40 RPM when the
valve is blocked, the system is not working properly.
Check the valve, hoses, and manifold passages for tight
connections and blockage. Insufficient engine speed
drop can also be caused by the wrong PCV valve being
installed.
On some engines, the evaporative emission control
(EVAP) vapor canister purges through the PCV line.
Leakage in the purge hose will cause poor test results.
Disconnect and plug the canister purge hose, then re-
peat the tests. If the PCV system passes the second
test, the problem is in the purge system.
PCV SYSTEM SERVICE
Service of the PCV system usually consists of cleaning
or replacing the filter, or replacing the connecting hoses
or the valve itself.
Filter Replacement
The PCV inlet air is filtered through the engine air filter
on some engines. Simply replace the element at the rec-
ommended interval. Other designs have a separate PCV
filter element that mounts in the air cleaner housing, fig-
ure 4-2. This may be a foam filter or a wire mesh screen,
which unless torn or otherwise damaged can be cleaned
and reinstalled. To service, remove the filter, wash with
solvent, air dry, then reinstall. Lightly oil a foam type fil-
ter with clean motor oil before installation.
Filters installed in the oil filler cap are usually made of
wire mesh. Remove the filler cap and soak the complete
cap and filter in solvent. Allow it to drain and dry in the
air. Do not dry with compressed air; this will damage the
wire mesh.
Hose Replacement
Any damaged or deteriorated hose must be replaced to
ensure proper system operation. Use only hose de-
signed for PCV and fuel system applications. Standard
heater hose cannot withstand the blowby vapors and will
quickly fail.
PCV VALVE REPLACEMENT
A PCV valve cannot be distinguished by its appearance;
internal valve characteristics are specifically calibrated
for each application. Always refer to the part number
when replacing a valve. When installing a valve, make
sure to fit it with the arrow indicating direction of flow
pointing toward the intake manifold. If the valve is mount-
ed in a rubber grommet, it must provide a snug fit. If the
grommet is hardened or cracked, replace it.
THERMOSTATIC VACUUM SWITCH TEST
A thermostatic vacuum switch is normally activated by
engine coolant or air temperature. The vacuum switch
may be opened or closed by high or low temperatures,
depending upon its use and the system design.
Coolant-controlled switches are tested with the engine
cold, and at normal operating temperature. In some
cases, a third check is made at higher than normal tem-
perature. Do not allow the engine to overheat. A typical
test procedure for a three-port switch is shown in figure
4-3.
SPARK DELAY VALVE TESTS
In many older model vehicles spark delay valves were
used to slow the vacuum advance signal to the distribu-
tor. Some of theses valves delayed vacuum by means of
a restricted
orifice
in the vacuum line, figure 4-4.
Test a delay valve by attaching a vacuum gauge to the
distributor side of the valve. Use a vacuum pump to
apply 10 to 15 in-Hg (69 to 103 kPa) of vacuum to the
valve inlet side. The gauge reading should rise slowly to
AIR CLEANER
COVER
PCV
FILTER
FILTER
ELEMENT
Fig. 4-2.
Separate PCV filter installed in the intake air filter housing.
Summary of Contents for ASE-A8
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