Air Injection System GMC Pickup R3500

DESCRIPTION

Air Injection Reaction (AIR) system is used to reduce carbon monoxide (CO) and hydrocarbon (HC) emissions. The AIR system provides additional oxygen to continue combustion process after exhaust gases leave the combustion chamber. The AIR system diverts air from exhaust manifold during increased RPM or when electrical malfunction is detected within the system.

Federal system, (over 10,000 GVW) used on 5.7L or 7.4L engines consist of 2 air pumps, an air filter, 2 High-flow Electric Air Control (HFEAC) valves, 2 check valves, a control module and necessary plumbing. The 7.4L engine also uses a control relay to operate "SERVICE ENGINE SOON" light.

California systems and all models under 10,000 GVW consist of one air pump, air filter, air injection tubes, diverter valve (over 10,000 GVW), an electric air control with Relief Tube valve (ECT, 4.3L and V8 engines, under 10,000 GVW) or an Electric Air Control valve (EAC, 2.8L engine), check valves, air manifold assembly and hoses connected to various components.

AIR PUMP

The belt driven air pump supplies air through a centrifugal filter fan to a diverter valve, ECA valve or ECT valve.

California Models (Over 10,000 GVW)

Under normal vacuum conditions, metering valve is held open by a spring on vacuum side of diaphragm. This allows air from engine to pass into exhaust manifold. During deceleration (very high vacuum), vacuum is applied to diaphragm to overcome spring tension, closing metering valve momentarily. During closed metering valve, air is diverted to air cleaner or silencer. (Scheme 175)

Scheme 175

Federal (Over 10,000 GVW)

The HFEAC valve is a diverter valve with an electric solenoid to combine electronic control to a normal diverter valve function. With ignition on, solenoid is energized through control module and air is directed to exhaust manifold.

During deceleration, when there is a rise in the manifold vacuum signal, air is directed to air cleaner or silencer, even though solenoid is energized. The solenoid is de-energized when there is a high RPM over a prolonged period or a corresponding electrical circuit failure. (Scheme 176)

Scheme 176

ELECTRIC AIR CONTROL (EAC) & ELECTRIC AIR CONTROL WITH RELIEF TUBE (ECT) VALVES

Note. On EAC valve, divert and signal tube locations are reversed from previous model year.

Scheme 177

When engine is cold or at wide open throttle, ECM energizes solenoid on valve and air is directed to exhaust manifold ports. When coolant temperature increases, solenoid is de-energized and air goes into air cleaner.

At higher engine speeds, air is directed to air cleaner through pressure relief valve (if equipped), even though solenoid may be energized. Air should not be entering exhaust manifold during "closed loop" mode.

During deceleration, the increased manifold vacuum signal directs air to air cleaner. Check valve on air injection pipe, prevents exhaust gases from entering air pump. Under rich mixture condition or "SERVICE ENGINE SOON" light is on, solenoid is de-energized. (Scheme 177)

DECELERATION CONTROL VALVE

To assist in preventing backfiring during high vacuum conditions, a deceleration valve is used. High vacuum draws valve diaphragm down and opens valve to allow air from air cleaner to flow into intake manifold. This process leans the mixture created by high vacuum.

Accelerate engine to approximately 1500 RPM and observe air flow from hose. If air flow increases as engine is accelerated, air pump is okay. If air flow does not increase or is not present, check belt tension and for leaky pressure relief valve. Air may be heard leaking with pump running. Replace as necessary.

CHECK VALVE

Remove check valve. Blow air through check valve away from air pump. Air should pass freely. Blow air through check valve toward air pump, air should not pass. Replace valve if not operating properly.

DIVERTER VALVE

Ensure air pump operates properly. Start engine. Air should enter exhaust ports. Check for manifold vacuum signal at valve with engine idling. Vacuum should be 10 in. Hg (34 kPa). During decel and high vacuum signal, air should go to air cleaner and silencer. Replace valve if any conditions are incorrect.

AIR CONTROL VALVE

1. Ensure air pump operates properly. Disconnect electrical connector at solenoid valve. Turn ignition on and check for 12 volts at connector. If voltage is not within specifications, check for open and repair as necessary.
2. Start engine. Air should go to air cleaner or silencer. Connect solenoid electrical connector. Air should go to exhaust manifold. Check manifold vacuum signal at valve with engine idling. Vacuum should be 10 in. Hg (34 kPa). During decel and high vacuum signal, air should go to air cleaner and silencer. Replace valve if operation is incorrect.

THROTTLE BODY INJECTION TYPE

Note. Due to the complexity of the electronic controls, for testing of "SERVICE ENGINE SOON" light, see AIR MANAGEMENT CHECK (ELECTRONIC AIR CONTROL VALVE) chart in appropriate article in the COMPUTERIZED ENGINE CONTROLS section.

"SERVICE ENGINE SOON" Illuminated (4.8L)

1. Disconnect air temperature switch. Install a jumper wire across harness terminals. Turn ignition on. Disconnect air divert solenoid electrical connector. Using a test light, check for power from Pink/Black wire to ground. (Scheme 179)
2. If test light illuminates, check for power across air divert solenoid harness terminals. If test light illuminates, circuit is okay, go to next step. If test light does not illuminate, go to step 4).
3. Using an ohmmeter, measure resistance across air divert solenoid terminals. If resistance is less than 20 Ohms, replace solenoid and valve.
4. Check continuity of Yellow wire between control module and air temperature switch. Check continuity of Brown wire between control module and air temperature switch. If continuity checks are okay, replace control module.
5. Connect air divert solenoid harness connector. Disconnect 2 connectors from control module. Using a test light, check for power between terminals "A" and "B" of 5-pin connector.
6. If test light does not illuminate, check for an open circuit to module connector. If test light illuminates, check for power between terminals "A" and "D" of 5-pin connector. If test light illuminates, check for a short to ground on Brown/White wire. If test light does not illuminate, go to next step.
7. Check for an open circuit on Yellow wire between air divert solenoid and control module. If Yellow wire is okay, replace control module.

No "SERVICE ENGINE SOON" Light (5.7L)

1. Disconnect control module connector. Turn ignition on. Connect a jumper wire between Brown/White wire and ground. (Scheme 180) The "SERVICE ENGINE SOON" light should illuminate. If light illuminates, go to step 3). If light does not illuminate, go to next step.
2. Check for an open circuit on Pink/Black wire to "SERVICE ENGINE SOON" light. Check for a bad bulb or an open in Brown/White wire to control module.
3. Connect a jumper wire between terminal "B" and "D" of control module connector. The "SERVICE ENGINE SOON" light should illuminate. If light does not illuminate, check for an open in Black ground wire. If light illuminates, replace control module.

"SERVICE ENGINE SOON" Light Illuminated (5.7L)

1. Turn ignition on. Disconnect each air divert solenoid electrical connector. Using a test light, check for power between Pink/Black wire and ground on each connector. (Scheme 180) If test light does not illuminate, check for an open circuit in Pink/Black wire to each solenoid.
2. If test light illuminates, check for power across air divert solenoid harness connectors. If test light illuminates. Circuit is okay. Using an ohmmeter. Measure solenoid resistance.
3. If resistance is less than 20 ohms, replace solenoid and valve. If test light does not illuminate, check for an open circuit on Brown wire or a faulty control module.
4. Connect solenoid electrical connectors. Disconnect control module connector. Using a test light, check for power between terminals "A" and "B". If test light does not illuminate, check for an open circuit to control module.
5. If test light illuminates. Check for power between terminals "A" and "D" of control module connector. If light illuminates, check for a short to ground in Brown/White wire. If light does not illuminate, replace control module.

Scheme 178

Scheme 179

Scheme 180

Scheme 181