384 Auto Engine Performance and Driveability
Copyright by Goodheart-Willcox Co., Inc.
Checking Emission-Control
Components
Emission-control components that can be checked
include the PCV system, evaporative emission control, EGR
valve, air pump and valves, and thermostatic air cleaner.
Many other emission-control components are part of the
fuel, ignition, or computer control system and should have
already been checked as part of those systems.
Checking the PCV System
The PCV system is probably the easiest emission com-
ponent to check. One simple test is to locate the PCV valve,
remove it from the engine, and shake it. Listen for a rattling
noise that indicates the valve is not stuck. If no rattle is
heard, the PCV valve is stuck and should be replaced.
A more accurate test can be performed on some PCV
valves with the engine running. Start the engine and remove
the PCV valve from the grommet that holds it to the valve
cover or crankcase inlet hose (if it has not been removed
already). Do not disconnect it from the hose leading to
the intake manifold. Place your thumb over the valve. You
should feel a strong vacuum and the engine speed should
slightly decrease when the vacuum is cut off. If this does not
occur, the PCV valve is defective or the hose is plugged.
If the PCV valve is defective or the hose to the valve is
clogged or collapsed, replace it. The relatively low cost of
these parts makes cleaning unnecessary, while also reduc-
ing the possibility of a comeback problem. PCV valve and
hose replacement is the reverse of removal.
Note: Some PCV valves are not clearly
visible when looking at the engine. Refer to
the service information for location of the
PCV valve. Some engines do not have a PCV valve.
Checking Evaporative Emission Control
Systems
Evaporative emissions systems are relatively trouble
free, but can develop four kinds of problems:
Flow restrictions can be caused by clogged fi lters,
inoperative fl ow control valves, or defective hoses.
Vacuum pressure buildup can be caused when the
tank vent system fails.
Figure 18-11. Comparing test results to a set standard shows
which readings are above or below allowable levels. This will
help determine where to start looking for the problem.
Gas
HC
CO
.41
.08
3.4 2.8
0.2
1.13
Standards (gpm)
Test Readings
NOX
Figure 18-12. A drive cycle must be performed before an emissions inspection and after the battery has been disconnected. The
steps shown here are generic, but are typical of the steps normally completed for a drive cycle.
Drive Cycle
Drive Status System Monitored
Cold start, coolant temperature 122°F
(50°C)
No system monitored, warm-up only
Idle 90 seconds in drive or neutral, A/C on HO2S heater, EVAP purge, secondary air,
fuel trim, misfire
Accelerate to 45 mph (72 kph),
1/2 throttle, A/C off
Fuel trim, misfire, HO2S monitor
Two minutes of steady throttle at 45 mph
(72 kph)
Misfire, EGR, secondary air, fuel trim,
EVAP purge
Decelerate to 20 mph (32 kph), no braking Fuel trim, EGR, misfire, EVAP purge
Accelerate to 50–60 mph (88–97 kph),
3/4 throttle
Fuel trim, EVAP purge, HO2S, misfire
Four minutes of steady throttle at 55–60 mph
(88–97kph)
Catalyst monitor, misfire, EGR, fuel trim,
HO2S
Decelerate to stop, no braking EGR, EVAP purge
End of Drive Cycle