Chapter
D
: Emission Control Systems Diagnosis and Repair
77
EXHAUST GAS TREATMENT
In addition to exhaust gas recirculation, many engines
use secondary air injection reaction (AIR) to reduce tail
pipe pollutants. Pumping fresh air into the exhaust as it
leaves the engine helps to complete combustion. Air in-
jection helps to oxidize any unburnt fuel in the exhaust
to reduce HC and CO emissions. Two AIR system de-
signs are used:
• Pump-type
• Pulse-type
PUMP-TYPE SYSTEMS
An air pump delivers a stream of fresh air to the exhaust,
figure 4-7. Although a few engines use an electric motor
to drive the air pump, figure 4-8, most are driven by a belt
off of the crankshaft. With the exception of belt adjust-
ment, there are no routine adjustments. However, man-
ufacturers do recommend periodic inspections to ensure
exhaust emissions are kept within legal limits.
Inspection
Inspect a pump-type AIR system as follows:
1. Check drive belt condition and tension.
2. Inspect all hoses and lines for loose connections,
cracking, brittleness, or burning.
3. Inspect the check valve for exhaust leakage. Look
for changes in the color of the metal that indicate
excessive heat.
4. Disconnect the pump hose at the check valve. Start
the engine and check for airflow from the open end
of the hose.
5. Raise engine speed to 1500 RPM and check for an
airflow increase.
6. With the engine running at fast idle, momentarily
pinch off the pump outlet hose and listen for the re-
lief valve open.
7. If a filter is used, remove it and check for clogging.
Fig. 4-7.
Belt-driven pump AIR system.
Fig. 4-8.
Electric motor driven AIR pump.
Summary of Contents for ASE-A8
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