Chapter 10: Emissions Equipment: A.I.R. System
These systems are used to reduce carbon monoxide (CO),
hydrocarbon (HC) and nitrous oxide (NOx) emissions. They also heat up the
catalytic converter quickly on engine start-up so conversion of exhaust gases will
A dual bed converter is used. It consists of a three way
catalyst (which controls all three emissions) in series with a two way catalyst
(which controls only HC and CO). Both are in one housing. A pipe between the two
converters allows air to be injected into the second (two way) converter to
increase it's efficency to futher control HC and CO.
A.I.R. Pump Operation:
The system includes an air pump, a control valve, a check
valve and neccessary plumbing.
- The air pump is driven by a belt on the front of the engine
and supplies air to the system.
- Intake air passes through a centrifugal filter fan at the
front of the pump; where foreign materials are separated from the air by
- Air flows from the pump through an ECM controlled valve
(called a control valve) to a check valve. The check valve prevents back flow
of exhaust into the pump in the event of an exhaust backfire or pump drive belt
An intregal valve, called an air control valve assembly, is
actually two valves or sections that have specific functions. Those sections will
be referred to as air divert and air switching valves. Each is controlled by a
solenoid vacuum valve.
Electric Divert/Electric Air Switching Valve (EDES), (5.0L)
This system uses vacuum operated, ECM controlled
valve which combine both the divert function and the A.I.R. switching function
in one housing.
- The air control (divert) valve provides air divert to the
air cleaner for converter protection or directs air to the switching valve.
- The air switching valve directs air to the exhaust ports
during cold engine operation, or anytime the fuel control system is in open
loop, and between converter beds during warm engine operation when the fuel
control system is in closed loop.
- When divert is needed, the ECM turns off the solenoid in the
air control section of the valve, causing air to be diverted to the air cleaner
- Divert occurs under the following conditions:
- Rich operating conditions.
- When the ECM recognizes a problem and sets the "CHECK
- During deceleration, very high vacuum.
- High RPM when air pressure exceeds the setting for the
relief valve in the air control valve.
5.0L VIN code Y and 9 engines use the same air control
system as explained for EDES valves. However the air divert and the switching
valves are separate valves.
Pressure Operated Electric Divert/Electric
Switching Valve (PEDES), (3.8L)
Divert and switching functions are electrically controlled
by the ECM. Pressure from the A.I.R. pump is used to operate the valve, and
operation is completly independent of manifold vacuum.
Operation of PEDEDS Valve:
- Air enters the body of the valve from the pump.
Air pressure builds against the control valve and for:
- Cold Mode - The port solenoid is energized which in turn
opens the port valve and allows flow to the exhaust ports.
- Warm Mode - The port solenoid is deenergized and the
converter solenoid is energized which closes the port valve and keeps the
converter valve seated, thus forcing flow past the converter valve and to
- Divert Mode - Both solenoids are deenergized which opens
the converter valve, allowing air to take the path of least resistance, ie.,
out the divert/relief tube to atmosphere.
The relief valve operates to limit overall system pressure.
Results of Incorrect A.I.R. System Operation
- If no air (oxygen) flow enters the exhaust stream at the
exhaust ports, or the converter pipe, HC and CO emission levels will be too
- Air flowing to the exhaust ports at all times could cause a
rich ECM command and increased temperature of the converter.
The air pump is a positive displacement vane type which is
permanently lubricated and requires no periodic mantainance.
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