Air Injection System - Vehicles Over 8500 Gvw GMC Pickup R1500

DESCRIPTION

Heavy duty emission engines with vehicle weight over 8500 GVW have an AIR System with increased air flow. System is used to reduce carbon monoxide (CO) and hydrocarbon (HC) emissions.

The air injection reaction (AIR) system provides additional oxygen to continue the combustion process after exhaust leaves the combustion chamber. System diverts air from the exhaust manifold at increased engine speed or when an electrical malfunction is detected.

System used on 4.8L engines consists of an air pump, air filter, air control valve, check valve, silencer, air temperature switch, control module and necessary plumbing.

System used on 5.7L and 7.4L engines consists of 2 air pumps, air filter, 2 air control valves, 2 check valves, control module and necessary plumbing. A control relay is used on 7.4L engines to operate the "SERVICE ENGINE SOON" light.

OPERATION

Air pump(s) is mounted on front of engine and is belt driven. Intake air flows through an external air filter to air pump(s). Air flow from pump(s) passes through control valve(s) and air pipe(s).

Air flow passes through check valve(s) and enters exhaust manifold. Purpose of check valve(s) is to prevent a reverse flow of exhaust gasses from damaging air pump in event of a backfire or pump drive belt failure.

AIR CONTROL VALVE

The high flow electric air control (HFEAC) valve uses a solenoid to combine electronic control with normal diverter valve function. With ignition switch "ON", solenoid is energized through control module. Air control operates as a standard diverter valve. With solenoid energized, air is directed to exhaust manifold.

During engine deceleration, manifold vacuum will increase. A strong vacuum signal will cause air to be directed to air cleaner or silencer even though solenoid is energized. Solenoid is de-energized when there is high engine speed over a prolonged time period or an electrical malfunction has occurred. (Scheme 48)

"SERVICE ENGINE SOON" LIGHT

A malfunction of control module, wiring harness or solenoid(s) will cause an amber "SERVICE ENGINE SOON" instrument panel light to illuminate. With ignition switch "ON" and engine not running, "CHECK ENGINE SOON" light will be "ON". This is used as a bulb check (except 7.4L models). When engine is started, light will remain on for 3-6 seconds and then turn off.

On 7.4L system, with ignition "ON" and engine not running, "SERVICE ENGINE SOON" light will come "ON" and stay "ON" for 1-2 seconds and then go "OFF". This is also a bulb check.

DECELERATION CONTROL

A deceleration (gulp) valve is used on AIR systems as an aid in preventing backfires during high vacuum conditions. High manifold vacuum draws deceleration valve diaphragm down and opens valve allowing air from air cleaner to flow into intake manifold. Incoming air leans air/fuel mixture during deceleration.

Scheme 48

When throttle valve is closed and engine RPM is high, high manifold vacuum draws an excessive amount of fuel from idle discharge ports. Deceleration valve effectively controls this temporarily rich mixture condition. (Scheme 49)

Scheme 49

Scheme 50

AIR PUMP

1. Air pump is permanently lubricated and requires no periodic maintenance. Accelerate engine and observe air flow from hose(s). If air flow increases as engine is accelerated, pump is operating satisfactorily.
2. If air flow does not increase or is not present, inspect for correct drive belt tension or leaking pressure relief valve. Air may be heard from leaking relief valve with pump running.

1. Ensure that air pump is working properly. Disconnect solenoid connector at valve. Turn ignition "ON". Check for 12 volts at connector. If no voltage is present, refer to diagnostic charts. (Scheme 57), (Scheme 58) and (Scheme 59). Start engine. Air should flow to air cleaner or silencer. Connect solenoid connector. Air should flow to exhaust ports.
2. Check for manifold vacuum signal at valve with engine idling. Vacuum should be 10" Hg (34 kPa). During deceleration and high vacuum signal conditions, air should flow to air cleaner and silencer. If airflow does not conform to specifications, replace air control valve.

CHECK VALVE

1. Inspect check valve whenever hose to valve is disconnected or if check valve failure is suspected.
2. If air pump is inoperative and shows signs of exhaust gases entering pump, check valve failure is indicated. Air flow must be in one direction only, toward exhaust manifold. If air flow is in both directions, replace check valve.

HOSES & PIPES

1. Inspect all hoses and pipes for holes or deterioration. Inspect for loose pipe connections and clamp tightness. Check for correct hose and pipe routing.
2. If a leak is suspected on pressure side of system or if a hose has been disconnected, use soapy water solution to check for leaks. With air pump running, bubbles will form if leak exists.

DECELERATION VALVE

1. Remove air cleaner. Plug air cleaner vacuum source. Connect tachometer. With engine running at specified idle speed, remove small deceleration valve signal hose from manifold vacuum source. Reconnect signal hose and listen for air flow through ventilation pipe and into deceleration valve. A drop in engine RPM will be noticed when signal hose is reconnected.
2. If air flow does not continue for at least one second or engine RPM does not drop noticeably, check deceleration valve hoses for restrictions or leaks. If no restrictions or leaks are found, replace deceleration valve. (Scheme 53), (Scheme 55) and (Scheme 56).

Scheme 51

AIR SYSTEM

1. To determine if excessive noise is fault of Air Injection Reactor System, operate engine with air pump drive belt removed. If excessive noise does not exist with belt removed, inspect pump for damage.
2. Inspect drive belt for wear, cracks or deterioration. Check for seized air pump. Check for improper pump mounting and bolt torque. Check for improper routing and connection of hoses. If none of these conditions exist and pump is still excessively noisy, replace air pump.

"SERVICE ENGINE SOON" LIGHT IS ON

Note. Illumination of "SERVICE ENGINE SOON" light indicates a malfunction of control module, solenoid or wiring. Check solenoid and module connectors for proper connection.

1. Disconnect air temperature switch. Install a jumper wire across switch terminals. With ignition on, disconnect each solenoid connector. Using a test light, check for a light from the Pink/Black wire to ground. If light does not illuminate, check for open at circuit No. 39 to solenoid.
2. If light illuminates, check for a light across terminals. Circuit is okay if there is a light. Check solenoid coil resistance. If coil resistance is less than 20 ohms, replace solenoid and valve.
3. If there is no light, check for open in circuit No. 900 to air temperature switch, open in circuit No. 436 or faulty control module.
4. Connect solenoid connectors. Disconnect both connectors at control module. Check for a light between terminals "A" and "B" of 5-pin connector. If test light does not illuminate, check for open circuit to module.
5. If test light illuminates, check for a light between 5-pin connector harness terminals "A" and "D". If test light illuminates, check for short to ground in circuit No. 419. If test light does not illuminate, check for open in circuit 900 between solenoid terminal "B" and module 2-pin connector terminal "A". If circuit No. 900 is not open, replace control module. (Scheme 58), (Scheme 59) and (Scheme 52).

DIAGNOSTIC CHART FOR 7.4L CARBURETED ENGINE "SERVICE ENGINE SOON" LIGHT "ON" AT ALL TIMES

1. Determine if power is available to air temperature switch. (Scheme 52)
2. Ensure power is available to circuit by eliminating air temperature switch. Check wiring between air temperature switch and solenoids.
3. Check wiring between solenoids and ground, including circuit inside control module.
4. Determine if problem is short to ground in "SERVICE ENGINE SOON" light circuit or malfunction in air management system.
5. Check for battery positive at "A" and ground at "B". This determines that power is available to control module.
6. Determine if ground signal is sent to relay because circuit No. 919 is grounded outside module.
7. Check for tachometer signal to control module.

Scheme 52

Removal

1. Secure pump pulley by compressing drive belt. Loosen pump pulley bolts. Loosen pump mounting bolt. Remove belt from pulley.
2. Disconnect hoses at rear of pump. If control valve is attached to pump, disconnect vacuum and electrical connections. Remove pump pulley. Remove pump. Remove control valve (if attached).

Installation

1. To install, reverse removal procedure. Tighten pump pulley bolts to 10 ft. lbs. (15 N.m). Retighten pump pulley bolts to specification within 10 minutes.
2. Install pump drive belt. Ensure belt is fully seated in grooves of A/C compressor, AIR pump, generator and crankshaft pulleys. Adjust belt tension to specification.

Scheme 53

Scheme 54

Scheme 55

Disconnect electrical connector from solenoid. Remove air outlet hoses from control valve. Disconnect manifold vacuum hose. Remove air control valve, gaskets and adapter.

To install, reverse removal procedure.

Removal & Installation

Release clamp and disconnect air hose from check valve. Remove check valve bracket. Unscrew check valve from air injection pipe. To install, reverse removal procedure.

Scheme 56

Remove hose and clamp from check valve. Remove check valve. Remove nuts attaching pipes-to-manifold. Remove pipe assembly. To install, reverse removal procedure.

Scheme 57

Scheme 58

Scheme 59

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS