Chapter 18 Diagnosis and Repair of the Emission Control and Exhaust Systems 391
Copyright by Goodheart-Willcox Co., Inc.
Before replacing the thermal vacuum valve, make sure
that the coolant level is not low. If coolant does not contact
the switch, the switch will not operate properly.
Checking Emissions Filters
Emissions fi lters usually will not cause driveability
problems unless they become completely plugged. If the
PCV fi lter becomes completely plugged, it will cause the
same symptoms as a plugged PCV valve, such as rough idle
and poor gas mileage. If the evaporative emissions fi lter
becomes plugged, the engine will not be able to draw air
through the evaporative emissions system and may exhibit
signs of a rich air-fuel mixture. If a problem is suspected
with an emissions fi lter, remove the fi lter and make a visual
check for obvious accumulations of dirt or oil.
Many emissions canisters and PCV systems do not
have a replaceable fi lter. For those systems with replace-
able fi lters, replacement is usually done as part of routine
maintenance. This is discussed in Chapter 21.
Testing Catalytic Converter Temperature
One simple test of catalytic operation is done with an
infrared thermometer. Operate the vehicle until it reaches
normal operating temperature. Then, run the engine at an
elevated speed (about 2500 rpm) for two minutes. Quickly
and safely raise the vehicle with the engine running. Point
an infrared thermometer at the catalytic converter inlet pipe,
Figure 18-28. After reading the inlet temperature, point the
infrared thermometer at the catalytic converter outlet pipe,
Figure 18-29. Compare the readings.
The outlet temperature should be at least 40°F to
100°F (5°C to 40°C) above the inlet temperature.
The outlet temperature should be above 500°F to
600°F (250°C to 300°C) with the engine at operating
temperature.
If the measured temperatures do not match these guidelines,
the catalyst is coated or worn out. If converter temperature
is above 1200°F (650°C), check for a rich air-fuel mixture
causing the converter to overheat.
Figure 18-25. A—Use a mirror to check the operation of the
valve in a thermostatic air cleaner. The fl ap should close as the
engine warms up. B—If the fl ap does not open or close, use a
vacuum pump to test the vacuum motor. (Subaru)
Mirror
Vacuum
motor
A
Create a vacuum pressure
with a vacuum pump.
Close the outside
air inlet.
B
Figure 18-26. The fl ap on a thermostatic air cleaner should
close off the outside air intake when the engine is cold.
Flap closed
Figure 18-27. Once the heater pellet has been heated by a heat
gun or by operating the engine for 5 to 10 minutes, the fl ap on a
thermostatic air cleaner should be open.
Flap open