Toyota Tercel 1984-1994 Repair Guide

Exhaust Gas Recirculation

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OPERATION



Used on 3A-C, 3E and 3E-E engines.

The EGR system reduces oxides of nitrogen. This is accomplished by recirculating some of the exhaust gases through the EGR valve to the intake manifold, lowering peak combustion temperatures.

The EGR vacuum modulator controls the EGR valve by modulating the vacuum signal with an atmospheric bleed. This bleed is controlled by the amount of exhaust pressure acting on the bottom of the EGR vacuum modulator (diaphragm).

Since recirculation of exhaust gas is undesirable at low rpm or idle, the system limits itself by sensing the exhaust flow. Under low load conditions, such as low speed driving, the exhaust pressure is low. In this state, the diaphragm in the modulator is pushed down by spring force and the modulator valve opens to allow outside air into the vacuum passage. The vacuum in the line is reduced, the EGR valve does not open as far, and the amount of recirculation is reduced.

Under high load conditions or high rpm driving, the exhaust pressure is increased. This pushes the modulator diaphragm upwards and closes the bleed valve. A full vacuum signal is transmitted to the EGR valve; it opens completely and allows full recirculation. The slight reduction in combustion temperature (and therefore power) is not noticed at highway speeds or under hard acceleration.

Some vehicles also control the EGR with a vacuum switching valve (VSV). This device allows the ECM to further control the EGR under certain conditions. The ECM will electrically close the VSV if the engine is not warmed up, the throttle valve is in the idle position or if the engine is under very hard acceleration. Aside from these conditions, this EGR system (late models) operates in accordance with the normal vacuum modulator function.

SERVICING



EGR Valve

See Figure 1

  1. Remove the EGR valve.
  2.  
  3. Check the valve for sticking and heavy carbon deposits. If a problem is found, clean or replace the valve.
  4.  
  5. Reinstall the EGR valve with a new gasket.
  6.  



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Fig. Fig. 1: The EGR valve should be cleaned of carbon deposits

Vacuum Modulator
3A-C ENGINES

See Figures 2 and 3

  1. Label and disconnect the two vacuum hoses from their ports.
  2.  
  3. Plug one port with your finger.
  4.  
  5. Blow air into the other port. Check that the air passes freely through the air filter side of the modulator.
  6.  
  7. Start the engine, maintain it at 3,000 rpm.
  8.  
  9. Repeat the steps above. Check that there is a strong resistance to air flow.
  10.  
  11. Reconnect the vacuum hoses to the proper locations.
  12.  



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Fig. Fig. 2: Modulator air flow with the engine stopped; 3A-C engines



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Fig. Fig. 3: Modulator air flow with the engine running at speed; 3A-C engines

3E AND 3E-E ENGINES

See Figures 4 and 5

  1. Label and disconnect the vacuum hoses from ports P , Q , and R of the EGR vacuum modulator.
  2.  
  3. Plug the P and R ports with your fingers.
  4.  
  5. Blow air into port Q . Check that the air passes freely through the air filter side of the modulator.
  6.  
  7. Start the engine, maintain it at 3,000 rpm for 3E engines or 2,500 rpm for 3E-E engines.
  8.  
  9. Repeat the steps above. Check that there is a strong resistance to air flow.
  10.  
  11. Reconnect the vacuum hoses to the proper locations.
  12.  



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Fig. Fig. 4: Modulator air flow with the engine stopped; 3E and 3E-E engines



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Fig. Fig. 5: Modulator air flow with the engine at speed; 3E and 3E-E engines

Vacuum Switching Valve

See Figures 6, 7, 8 and 9

Used on 3E-E engines.

  1. The vacuum switching circuit is checked by blowing air into the pipe under the following conditions:
    1. Connect the vacuum switching valve terminals to battery voltage.
    2.  
    3. Blow into the tube and check that the VSV switch is open.
    4.  
    5. Remove battery voltage from the terminals.
    6.  
    7. Blow into the tube and check that the VSV switch is closed (no flow).
    8.  

  2.  
  3. Check for a short circuit within the valve. Using an ohmmeter, check that there is no continuity between the positive terminal and the VSV body. If there is continuity, replace the VSV.
  4.  
  5. Check for an open circuit. Using an ohmmeter, measure the resistance (ohms) between the two terminals of the valve. The resistance should be 38-44- at 68°F (20°C). If the resistance is not within specifications, replace the VSV.
  6.  

The resistance will vary slightly with temperature. It will decrease in cooler temperatures and increase with heat, slight variations due to temperature range are not necessarily a sign of a failed valve.

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Fig. Fig. 6: Air should pass through the VSV with battery voltage applied



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Fig. Fig. 7: With battery voltage disconnected, there should be no air flow



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Fig. Fig. 8: Checking the VSV for a short circuit



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Fig. Fig. 9: Checking for an open circuit

Bi-metal Vacuum Switching Valve

See Figures 10, 11, 12 and 13

Used on 3E engines.

Despite the impressive name, the BVSV valve does nothing more than allow vacuum to flow through the system depending on engine coolant temperature. The bi-metallic element within the switch reacts to temperature changes, opening or closing the valve at a pre-determined level. To test the valve:

  1. Drain the coolant from the radiator into a suitable container.
  2.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Label and disconnect the hoses from the BVSV.
  2.  
  3. Remove the valve.
  4.  
  5. Using cool water, cool the threaded part of the valve to below 104°F (40°C).
    1. M/T - check that air flows from port M to ports L and N.
    2.  
    3. A/T - check that air flows through the ports
    4.  

  6.  
  7. Using warm water, heat the threaded part of the valve to above 129°F (54°C)and blow into the ports again. The valve should not allow air to flow.
  8.  
  9. Apply liquid sealer to the threads of the BVSV and reinstall it. Connect the vacuum lines.
  10.  
  11. Refill the radiator with coolant.
  12.  



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Fig. Fig. 10: BVSV air flow when below its calibrated temperature; 3E engines with manual transaxle



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Fig. Fig. 11: BVSV air flow when below its calibrated temperature; 3E engines with automatic transaxle



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Fig. Fig. 12: BVSV air flow when above its calibrated temperature; 3E engines with manual transaxle



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Fig. Fig. 13: BVSV air flow when above its calibrated temperature; 3E engines with automatic transaxle

Thermostatic Vacuum Switching Valve

See Figures 14, 15 and 16

Used on 3A-C engines.

  1. Drain the cooling system.
  2.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Remove the thermostatic vacuum switching valve (TVSV).
  2.  
  3. Cool the thermostatic vacuum switching valve to below 45°F (7°C).
  4.  
  5. Check that air flows from pipe J to pipes M and L , and flows from pipe K to pipe N .
  6.  
  7. Heat the thermostatic vacuum switching valve to 63-122°F (17-50°C), generally room temperature.
  8.  
  9. Check that air flows from pipe K to pipes N and L and flows from pipe J to pipe M .
  10.  
  11. Heat the TVSV to above 154°F (68°C).
  12.  
  13. Check that air flows from the pipe K to pipes M and L , and does NOT flow from pipe J to any other pipes.
  14.  
  15. Apply liquid sealer to the threads of the TVSV and reinstall.
  16.  
  17. Refill the cooling system.
  18.  
  19. If a problem is found with any of the above procedures, replace the valve
  20.  



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Fig. Fig. 14: TVSV air flow at low temperature; 3A-C engines



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Fig. Fig. 15: TVSV air flow at moderate temperature; 3A-C engines



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Fig. Fig. 16: TVSV air flow at high temperature; 3A-C engines

Check Valve

See Figure 17

Inspect the check valve (one-way valve) by gently blowing air into each end of the valve or hose. Air should flow from the orange pipe to the black pipe but SHOULD NOT flow from the black pipe to the orange pipe.



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Fig. Fig. 17: Check valve air flow

REMOVAL & INSTALLATION



See Figures 18 and 19

EGR equipment is generally simple to work on and easy to get to on the engine. The air cleaner assembly will need to be removed. Always label each vacuum hose before removing it - they must be replaced in the correct position.

Most of the valves and solenoids are made of plastic. Be very careful during removal not to break or crack the ports; you have NO chance of gluing a broken fitting. Remember that the plastic has been in a hostile environment (heat and vibration); the fittings become brittle and less resistant to abuse or accidental impact.

EGR valves are generally held in place by two bolts. The bolts can be difficult to remove due to corrosion. Once the EGR valve is off the engine, clean the bolts and the bolt holes of any rust or debris. Always replace the gasket any time the valve is removed.



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Fig. Fig. 18: On some engines, it may be necessary to remove the exhaust gas crossover pipe before removing the EGR valve



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Fig. Fig. 19: EGR valves are usually secured with two bolts

 
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