Mazda 323/626/929/GLC/MX-6/RX-7 1978-1989

Rotary Engine Air Injection System

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OPERATION



See Figures 1, 2 and 3

The air injection system used on the Mazda rotary engine differs from the type used on a conventional piston engine in two respects:

  1. Air is not only supplied to burn the gases in the exhaust ports, but is also used to cool the thermal reactor/exhaust manifold.
  2.  



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Fig. Fig. 1: Air injection system-1979-80 RX-7

  1. A three-way air control valve is used in place of the conventional anti-backfire and diverter valves. It contains an air cutout valve, a relief valve, and a safety valve.
  2.  

Air is supplied to the system by a normal vane-type air pump. The air flows from the pump to the air control valve, where it is routed to the air injection nozzles to cool the thermal reactor/exhaust manifold or, in the case of a system malfunction, to the air cleaner. A check valve, located beneath the air control valve seat, prevents the back-flow of hot exhaust gases into the air injection system, in the event of air pressure loss.

Air injection nozzles are used to feed air into the exhaust ports, just as in a conventional piston engine.

On 1979-80 RX-7s, an air pump feeds fresh air into the hot exhaust gas as the gas leaves the exhaust ports. This burns the HC and CO in the exhaust gas. The system works as follows: The air pump draws in fresh air from the air cleaner and sends it to the air control valve, which routes it through the heat exchanger and into the exhaust ports. Not all of the air from the pump follows this path, however; some of the air is, at times, sent through the outer shell of the thermal reactor to keep the reactor from reaching destructively high temperatures. At other times, excess air from the pump is fed back into the air cleaner by the air control valve.



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Fig. Fig. 2: Air injection system-1981-83 RX-7



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Fig. Fig. 3: Cross-section of the air control valve-1979-80 RX-7

When the air from the air pump passes through the heat exchanger, it is pre-heated so that cold air is not pumped into the exhaust ports, which would lower the basic temperature in the exhaust system and affect the thermal reactor's ability to consume noxious gases. The fresh air injected into the exhaust ports adds oxygen to the exhaust gases, and they begin to burn as they pass into the thermal reactor. By the time the gases pass out of the thermal reactor, the previously unburned hydrocarbons and the carbon monoxide have been brought down to legal emission levels.

On 1981-89 RX-7s, the system used on these models replaces the thermal reactor with two catalytic converters (No.1 monolith and No. 2 monolith) and a reactive exhaust manifold. The system retains the air pump and the air control valve.

Air is pulled in from the air cleaner by the air pump and sent to the air control valve, where, according to engine operating conditions, the air is either sent into the exhaust ports or directed down to the dual bed-type catalyst. Excess air is sent back to the air cleaner. The air-burned hydrocarbons and carbon monoxide ignite these unused gases in much the same way the thermal reactor does on 1979-80 RX-7s. The air control valve sends air to the exhaust ports, mainly during deceleration and low engine speeds when HC and CO tend to be produced in large amounts. During this phase, the catalysts act as backup units to insure that fewer noxious gases are produced.

At the middle engine speeds, the air control valve routes air down to the two-bed catalyst. Air is injected through a nozzle between the two pellet beds of the rear catalyst. When the exhaust port air is stopped, the front bed of the rear catalyst processes oxides of nitrogen (NOx), while the rear bed, with the help of the injected fresh air, oxidizes hydrocarbons and carbon monoxide. The monolithic catalyst, located in front of the two-bed catalyst, acts as a backup system for the two-bed unit.

COMPONENT TESTING



Air Pump

See Figures 4 and 5

  1. Check the air pump drive belt tension by applying 22 lbs. (10 kg) of pressure halfway between the water pump and air pump pulleys. The belt should deflect 0.28-0.35 in. (7-9mm). Adjust the belt if necessary, or replace if it is cracked or worn.
  2.  
  3. Remove the belt and turn the pump by hand. If it has seized, the pump will be very difficult or impossible to turn.
  4.  



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Fig. Fig. 4: Test connections for the RX-7's air pump

Disregard any chirping, squealing or rolling sounds coming from inside the pump; these are normal when it is being turned by hand.

  1. Check the hoses and connections for leaks. Soapy water, applied around the area is question, is a good method of detecting leaks.
  2.  
  3. Connect a pressure gauge between the air pump and the air control valve with a T-fitting.
  4.  



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Fig. Fig. 5: After confirming the air pump's operation, disconnect the pressure gauge from the air control valve and seal off the T-fitting-RX-7

  1. Plug the other hose connections (outlets) on the air control valve, as illustrated. A gauge set which is similar to the illustrated rig (Mazda Part No. 49-2113-010B or equivalent) is available to test the air pump.
  2.  


CAUTION
Be careful not to touch the thermal reactor/exhaust manifold; severe burns will result.

  1. Connect a tachometer to the engine and check the idle speed. If the idle speed is not within specifications, adjust as necessary. With the engine at 800 rpm, the pressure gauge should read 1.64 psi (3.34 in. Hg). Replace the air pump if it is less than this.
  2.  
  3. If the air pump is not defective, leave the pressure gauge connected, but unfasten the connections at the air control valve and plug or cap the T-fitting, as shown, before proceeding with the next test.
  4.  

Air Control Valve
1979-80 RX-7

See Figures 6, 7 and 8

The air control valve on 1979-80 models consists of three valves: No. 1 relief valve, No. 2 relief valve, and an anti-afterburn valve. The No. 1 relief valve controls the flow of cooling air to the thermal reactor and is controlled by air pump air pressure. The No. 2 relief valve controls fresh air flow into the exhaust ports when closed, and re-routes excess fresh air back into the air cleaner when open. The anti-afterburn valve allows additional air into the intake manifold to prevent afterburn when the ignition is turned OFF .



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Fig. Fig. 6: Location of the air control valve-1979-80 RX-7

Testing of the air control valve is performed as follows:

  1. Check all hoses and vacuum sensing tubes for loose connections and damage. Make sure the air pump drive belt is properly adjusted.
  2.  
  3. Check that the air control valve is attached to the carburetor tightly.
  4.  



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Fig. Fig. 7: Disconnect the vacuum sensing tube from the relief solenoid valve-RX-7



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Fig. Fig. 8: Check the air control valve by placing a piece of paper in front of it-1979-80 RX-7

  1. Connect a tachometer to the engine, and disconnect the vacuum sensing tube from the relief solenoid valve.
  2.  

The relief solenoid valve has a blue dab of paint on its body.

  1. Disconnect the air hose between the air cleaner and the air control valve at the air cleaner, then start the engine and run it at idle.
  2.  
  3. Place a finger over the air hose opening and verify that air does not flow out of the opening.
  4.  
  5. Reconnect the vacuum sensing tube to the relief solenoid valve and gradually increase engine speed. Air should start to flow out of the air hose when the engine speed reaches about 1,300 rpm.
  6.  
  7. Stop the engine and remove the air pipe between the air control valve and the thermal reactor. It will be warm, so wait a few minutes and be careful.
  8.  
  9. Start the engine and run it at idle. Check to see that air does not flow out from the air control valve by placing a piece of paper in front of the valve, as shown in the illustration.
  10.  
  11. Increase engine speed to 4,500 rpm; air should flow out of the air control valve.
  12.  

If the results for any of these tests differ from the information given here, the air control valve is not working properly and should probably be replaced.

1981-83 RX-7

See Figure 7

The air control valve consists of an air relief valve, an air switching valve and a No. 1 anti-afterburn valve. The air relief valve controls fresh air flow into the exhaust ports when closed, and re-routes excess fresh air back into the air cleaner when open. The air switching valve switches the flow of fresh air back and forth between the exhaust ports and the two-bed catalyst according to engine demand. The anti-afterburn valve allows additional air into the intake manifold to prevent afterburn when the ignition is turned OFF .

  1. Check that all solenoid valve connections are tight and that the air pump drive belt is adjusted properly.
  2.  
  3. Make sure the air control valve is firmly attached to the engine.
  4.  
  5. Connect a tachometer to the engine. Disconnect the relief solenoid valve vacuum sensing tube and connect the tube to a suitable vacuum source.
  6.  

The relief solenoid valve has a blue dab of paint on its body.

  1. Disconnect the hose running from the air control valve to the air cleaner at the air cleaner.
  2.  
  3. Start the engine and run it at idle; no air should be flowing through the hose when the choke is off and the engine is warm.
  4.  
  5. Slowly raise the engine rpm. Air should now begin to flow through the hose when the vacuum is removed from the sensing tube.
  6.  
  7. Reconnect the vacuum source to the relief solenoid valve vacuum sensing tube.
  8.  
  9. Set the engine speed to 2,500 rpm with the throttle, and disconnect the vacuum sensing tube from the switching solenoid valve (gray painted valve); air should flow through the air hose. Air should stop flowing when this vacuum tube is reconnected.
  10.  

1984-89 RX-7

See Figures 9, 10 and 11

The air control valve functions to direct intake air to one of three locations: exhaust port, main converter, or relief air silencer. The air control valve system consists of the relief valve, switching valve and anti-afterburn valve.

  1. Warm up the engine to normal operating temperature. Connect a tachometer to the engine and check/adjust the idle speed.
  2.  



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Fig. Fig. 9: Relief solenoid valve location-1986-89 non-turbo RX-7



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Fig. Fig. 10: Switching solenoid valve location-1986-89 non-turbo RX-7

On 1987-89 turbocharged vehicles equipped with ABS, disconnect the air and vacuum hoses on the air control valve from the turbocharger. Plug the ends of the hoses before disconnecting the air control valve hose in the next step.

  1. Disconnect the hose that runs from the air silencer to the air control valve at the valve.
  2.  
  3. Place a finger over the air control outlet port.
  4.  
  5. Have an assistant gradually increase the engine speed to 1,500-2,500 rpm for 1984-89 non-turbo vehicles, or 3,750-3,850 rpm for 1986-89 turbocharged vehicles.
  6.  
  7. Run the engine at idle speed.
  8.  



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Fig. Fig. 11: Relief solenoid valve connector-1986-89 RX-7 turbo

  1. On 1984-89 non-turbocharged models, locate the vacuum hose that runs between the relief solenoid valve and the air control valve. Disconnect the hose from the relief solenoid valve. On 1986-89 turbocharged vehicles, unfasten the relief solenoid valve connector.
  2.  

The relief solenoid valve is identified by a blue tab or blue dab of paint on some models.

  1. Make sure air flows from the relief solenoid valve at 1,200 rpm or greater. Reattach the vacuum hose or the electrical connector.
  2.  
  3. Locate the split air hose that runs from the intake manifold to the check valve. Disconnect the hose from the check valve and place a finger over the port. Disconnect the vacuum hose from the switching solenoid valve.
  4.  
  5. Make sure air flows from the switching solenoid valve port.
  6.  
  7. If air flow is not as described, replace the air control valve.
  8.  

Check Valve

See Figures 12 and 13

The check valve prevents exhaust gases from traveling backwards into the air pump and damaging it. There are two check valves used in the secondary air injection system. One is installed in the intake manifold, and the other is located inline between the intake manifold and catalytic converter. Both check valves are tested the same way and perform the same protective function.

  1. Warm the engine to normal operating temperature, and connect a tachometer to the engine.
  2.  



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Fig. Fig. 12: Intake manifold-mounted check valve-1985-87 fuel injected RX-7



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Fig. Fig. 13: Exhaust gas leakage at the air control valve's air inlet indicates a defective check valve

  1. Disconnect the hose between the air pump and the air control valve at the air control valve. Disconnect the switching solenoid valve coupler (1981 models). If testing the catalytic converter check valve, locate the hose that runs from the intake manifold to the converter at the rear of the intake manifold, and disconnect it.
  2.  
  3. Slowly increase the engine speed to 1,500 rpm and watch for exhaust gas leakage at the air inlet fitting on the air control valve. If exhaust gas is coming out of the inlet, replace the check valve.
  4.  

REMOVAL & INSTALLATION



Air Pump

See Figure 14

  1. If applicable, remove the air cleaner assembly from the carburetor.
  2.  
  3. Disconnect the air supply hoses from the pump.
  4.  
  5. Loosen and remove the air pump strap bolt.
  6.  
  7. Push the pump toward the engine to slacken belt tension, then remove the drive belt from the pulley.
  8.  



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Fig. Fig. 14: Air pump mounting-RX-7

  1. Unfasten the pump securing bolts and remove the pump.
  2.  


CAUTION
Do not pry on the air pump housing during removal and do not clamp the housing in a vise once the pump has been removed. Any type of heavy pressure applied to the housing will distort it.

To install:
  1. Position the pump on its mounting, then install the mounting bolts. Snug the bolts just enough to allow movement for adjustment.
  2.  
  3. Install and properly tension the drive belt by moving the air pump, then tighten the bolts.
  4.  

While applying 22 lbs. of pressure halfway between the water pump and air pump pulleys, the belt should deflect 0.28-0.35 in. (7-9mm).

  1. Connect the air supply hoses.
  2.  
  3. If applicable, install the air cleaner assembly.
  4.  

Air Control Valve
1979-85 CARBURETED RX-7
  1. Remove the hot air duct.
  2.  
  3. Disconnect the air hose from the valve.
  4.  
  5. Disconnect the electrical lead from the port air solenoid valve.
  6.  
  7. Unfasten the retaining bolts and remove the valve.
  8.  

To install:
  1. Position the air control valve and secure with retaining bolts.
  2.  
  3. Connect the port solenoid valve electrical lead.
  4.  
  5. Connect the air hose to the valve and install the hot air duct.
  6.  

1984-89 FUEL INJECTED RX-7

See Figure 15

  1. On 1984-85 models, remove the throttle chamber funnel.
  2.  
  3. Detach all solenoid valve connectors. (The number of connectors will vary depending on the year.)
  4.  



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Fig. Fig. 15: Air control valve mounting-fuel injected RX-7

  1. Unfasten and remove the valve.
  2.  

To install:
  1. Position the air control valve and secure with retaining bolts.
  2.  
  3. Fasten all the wiring connectors.
  4.  
  5. On 1984-85 models, install the throttle chamber funnel.
  6.  

Check Valve
  1. Remove the air control valve, as described earlier in this section.
  2.  
  3. Unscrew and remove the check valve and gasket from the manifold.
  4.  

To install:
  1. Screw the check valve into the manifold, using a new gasket.
  2.  
  3. Install the air control valve, as described above.
  4.  

Air Injection Nozzle
  1. Remove the gravel shield from underneath the car.
  2.  
  3. Remove the oil pan removal procedure, as detailed in Engine & Engine Overhaul of this repair guide.
  4.  
  5. Unbolt the air injection nozzles from both ends of the rotor housing.
  6.  

To install:
  1. Attach and fasten the air injection nozzles to both ends of the rotor housing.
  2.  
  3. Install the oil pan, as detailed in Engine & Engine Overhaul .
  4.  
  5. Fasten the gravel shield to the bottom of the car.
  6.  

 
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