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

Rotary Engine Deceleration Control System

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OPERATION



RX-7 With Carburetor

The deceleration control system on manual transmission models consists of the anti-afterburn valve (two used on 1981 and later models), the dashpot and its delay valve, and the coasting valve. On automatic transmission models, only the anti-afterburn valve is used.

The single (or primary) anti-afterburn valve is part of the air control valve. Please refer to the preceding Air Injection System coverage for additional information.

On 1981 and later models, the second anti-afterburn valve is located to the rear of the carburetor. It controls air intake to the rear rotor, while the anti-afterburn valve (in the air control valve) controls air intake to the front rotor.

The dashpot acts to slow down the closing speed of the throttle valve in the carburetor when the accelerator pedal is released. This helps prevent engine misfire. The dashpot also acts as an emission control device.

The coasting valve allows additional air into the intake manifold to prevent engine misfire during deceleration at engine speeds over 1,150 rpm. It is regulated by the control unit and the idle switch on the carburetor.

RX-7 With Fuel Injection

The deceleration control system on fuel injected RX-7s consists of a fuel cut-off circuit, throttle sensor, anti-afterburn valve and dashpot.

The fuel cut-off circuit stops flow to the fuel injectors while decelerating during certain engine speed ranges.

The throttle sensor measures the opening angle of the primary throttle valve; it sends this information to the control unit, which determines the proper air/fuel mixture needed by the engine during deceleration.

The anti-afterburn valve is an integral component of the air control valve. The valve feeds fresh air into the rear port during deceleration.

The dashpot gradually shuts the throttle valve during deceleration.

COMPONENT TESTING



These systems are highly complex and are covered by an extended warranty. Therefore, only simple adjustments are included here.

Anti-Afterburn Valve
1979-80 RX-7

See Figure 1

  1. Check all hoses and vacuum sensing tubes for improper connections and signs of wear; replace as necessary.
  2.  
  3. Disconnect the hose which runs from the air control valve to the air cleaner at the air cleaner assembly.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Air control valve with its integral anti-afterburn valve-1979 RX-7 shown

  1. Disconnect the vacuum sensing tube from the relief solenoid valve, which can be identified by the blue spot of paint on its body.
  2.  
  3. Start the engine and run it at idle. Place your finger over the disconnected hose to the air cleaner; no vacuum should be present.
  4.  
  5. Detach the electrical connection of the anti-afterburn solenoid valve; vacuum should now be present in the hose. If not, the anti-afterburn valve, its solenoid valve or its vacuum lines are defective and must be replaced.
  6.  

1981-85 RX-7 WITH CARBURETOR

Test the No. 1 anti-afterburn valve as follows:

  1. Warm up the engine and run it at idle speed.
  2.  
  3. Locate the hose that runs between the air control valve and the air pump. Disconnect the hose at the air pump.
  4.  
  5. Place a finger over the opening of the air hose and check that no air is sucked into the hose at idle speed.
  6.  
  7. Have an assistant increase the idle speed to just over 3,000 rpm, then quickly release the accelerator pedal. Make sure air is sucked into the hose for a few seconds while the engine is decelerating. If not, replace the air control valve.
  8.  

Test the No. 2 anti-afterburn valve as follows:

  1. Warm up the engine and run it at idle speed.
  2.  
  3. Locate the hose that runs between the air cleaner and the No. 2 anti-afterburn valve. Disconnect the hose at the air cleaner.
  4.  
  5. Place a finger over the opening of the air hose and check that no air is sucked into the hose at idle speed.
  6.  
  7. Have an assistant increase the idle speed to just over 3,000 rpm, then quickly release the accelerator pedal. Make sure air is sucked into the hose for a few seconds while the engine is decelerating. If not, replace the air control valve.
  8.  

1984-89 RX-7 WITH FUEL INJECTION
  1. Warm up the engine and run it at idle speed.
  2.  
  3. Locate the hose that runs between the air control valve and the air pump. Disconnect the hose at the air pump.
  4.  
  5. Place a finger over the opening of the air hose and check that no air is sucked into the hose at idle speed.
  6.  
  7. Have an assistant increase the idle speed to just over 3,000 rpm, then quickly release the accelerator pedal. Make sure air is sucked into the hose for a few seconds while the engine is decelerating. If not, replace the air control valve.
  8.  

Dashpot
1979 RX-7

See Figure 2

This test procedure applies only to vehicles equipped with a manual transmission.

  1. Remove the air cleaner assembly.
  2.  
  3. Check all vacuum hoses for tears and/or deterioration. Replace as required.
  4.  
  5. Make sure the dashpot plunger rod does not keep the throttle lever from returning to its idle stop when closed.
  6.  



Click image to see an enlarged view

Fig. Fig. 2: A dashpot affects closing of the throttle valve on some RX-7s

  1. Quickly operate the throttle lever; the dashpot plunger rod should quickly extend.
  2.  
  3. Release the throttle lever; the plunger rod on the dashpot should slow its return to the idle position.
  4.  
  5. Connect a tachometer to the engine.
  6.  
  7. Start and run the engine until it reaches normal operating temperature. Make sure the idle speed is within specifications; adjust as necessary.
  8.  
  9. Disconnect the vacuum sensing tube from the top of the dashpot and move the throttle lever away from the dashpot plunger rod. Close the vacuum inlet at the top of the dashpot with your finger.
  10.  
  11. Release the throttle lever and check the engine speed at which the dashpot stops moving after it has been pushed in by the throttle lever. This speed should be 1,650-1,850 rpm. If not, loosen the locknut on the dashpot and adjust by turning the dashpot body. Repeat Step 9 to verify the adjustment.
  12.  

1980-85 RX-7

On 1980-82 models, this test procedure applies only to vehicles equipped with a manual transmission.

  1. Remove the air cleaner assembly (carbureted models only).
  2.  
  3. Check to see that the dashpot does not keep the throttle lever from returning to the idle stop.
  4.  
  5. Quickly operate the throttle lever fully; when the throttle lever is open, the dashpot plunger rod should quickly extend.
  6.  
  7. Release the throttle lever. The lever should quickly snap closed until it hits the dashpot plunger rod, then slowly close until it reaches its stop.
  8.  
  9. Connect a tachometer to the engine. Run the engine until it reaches normal operating temperature, then make sure the idle speed is correct.
  10.  
  11. Move the throttle lever until it is away from the dashpot plunger rod.
  12.  
  13. Slowly close the throttle lever and note the engine speed when the throttle lever just touches the dashpot plunger rod. If engine speed is not 3,500-3,900 rpm for 1980 models, 3,800-4,200 rpm for 1981-85 carbureted models, or 2,350-2,650 rpm for fuel injected models, loosen the locknut and adjust the dashpot by turning it until its plunger rod is in the correct position.
  14.  

1986-89 RX-7
  1. On turbocharged models, drain the cooling system and remove the intercooler.
  2.  
  3. Manually open the throttle valve fully, then push the dashpot actuating rod with your finger; verify that the rod retracts slowly into the dashpot.
  4.  
  5. Release the rod and check that it returns quickly to its original position.
  6.  
  7. If the dashpot does not operate as described, adjust or replace it. (Dashpot adjustment is described later in this section.)
  8.  

Coasting Valve
1979-80 RX-7 WITH MANUAL TRANSMISSION

See Figure 3

The coasting valve allows additional air into the intake manifold to prevent engine misfire during deceleration at engine speeds over 1,150 rpm. It is regulated by the engine control unit and the idle switch on the carburetor.

  1. Connect a tachometer to the engine.
  2.  
  3. Warm the engine to its normal operating temperature.
  4.  

  1. Detach the electrical connection from the coasting valve, then attach a voltmeter to the harness side of the connection. Disconnect the vacuum sensing tube from the dashpot diaphragm on 1979 models.
  2.  
  3. Start the engine and increase the engine speed to 3,000 rpm, using the throttle. Quickly release the throttle lever; current flow should stop when the engine speed falls below 1,050-1,250 rpm (1,000-1,200 rpm on Canadian models). Shut off the engine.
  4.  
  5. Disconnect the voltmeter, then detach the air hose (running from the coasting valve to the air cleaner) at the air cleaner assembly.
  6.  

Do not yet reconnect the coasting valve electrical connection.

  1. Start the engine. There should be no vacuum at the air hose. Activate the coasting valve by attaching jumper wires to its electrical connection from the battery; when the engine is running, vacuum should be present in the air hose.
  2.  



Click image to see an enlarged view

Fig. Fig. 3: Testing the coasting valve-1979-80 RX-7

1981-85 CARBURETED RX-7
  1. Warm up the engine to its normal operating temperature.
  2.  
  3. Disconnect the hose from the coasting valve to the air cleaner at the air cleaner assembly.
  4.  
  5. With the engine running at idle, place a finger over the hose opening and verify that air is not drawn into the hose.
  6.  
  7. Detach the connector from the shutter solenoid valve; air should be drawn into the disconnected hose as the idle roughens. At that same moment, check that the coasting valve rod retracts into the coasting valve approximately 0.4 in. (10mm).
  8.  

ADJUSTMENTS



Throttle Positioner
  1. Disconnect the wiring from the coasting valve solenoid, and connect the solenoid directly to the car battery.
  2.  
  3. Loosen the locknut on the solenoid adjuster.
  4.  
  5. Rotate the adjuster until an idle speed of 900-1,000 rpm is obtained after releasing the throttle from an engine speed of 2,000 rpm.
  6.  
  7. Tighten the locknut carefully once the proper idle speed has been obtained.
  8.  
  9. Disconnect the jumper wires from the battery, then reattach the coasting valve solenoid's electrical connector.
  10.  

As soon as the solenoid is disconnected from the battery, idle speed should drop to 800 rpm.

Idle Switch
  1. Warm up the engine until the water temperature is at least 159°F (71°C).
  2.  
  3. Make sure that the mixture and idle speed are adjusted properly.
  4.  
  5. Adjust the idle speed to 1,075-1,100 rpm (manual transmission) or 1,200-1,300 rpm (automatic transmission), by rotating the throttle adjusting screw.
  6.  
  7. Rotate the idle switch adjusting screw until the switch changes from the OFF to ON position.
  8.  
  9. Slowly turn the idle switch adjusting screw back to the point where the switch just changes from ON to OFF.
  10.  
  11. Turn the throttle screw back so that the engine returns to normal idle.
  12.  

Be sure that the idle switch turns ON when the idle speed is still above 1,000 rpm.

Dashpot
1986-89 NON-TURBO RX-7
  1. Start the engine and allow it to warm up to normal operating temperature at idle speed.
  2.  
  3. Connect a tachometer to the engine and increase the engine speed to 3,000 rpm.
  4.  
  5. Slowly decrease the engine speed and verify that the dashpot actuating rod makes contact with the throttle lever at 2,700-3,100 rpm.
  6.  
  7. To adjust the dashpot, loosen the locknut and rotate the dashpot body clockwise or counterclockwise until the rod makes contact with the lever at the specified rpm.
  8.  

1986-89 RX-7 TURBO

See Figure 4

  1. Drain the cooling system and remove the intercooler.
  2.  
  3. Detach the throttle sensor connector.
  4.  



Click image to see an enlarged view

Fig. Fig. 4: Checking dashpot resistance-1986-89 RX-7 turbo

  1. Attach an ohmmeter to terminals A and B of the throttle sensor connector, as shown in the illustration. Set the meter to the 1000x scale.
  2.  
  3. Manually separate the dashpot actuating rod from the throttle lever and observe the reading on the meter. As the rod and lever separate, the resistance should be 1.8-3.8 kilohms. If the reading is not as specified, adjust by loosening the locknut on top of the dashpot and rotating the dashpot body either clockwise or counterclockwise, until the proper resistance is obtained. Once the adjustment is complete, tighten the locknut.
  4.  

 
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