Mazda Trucks 1987-1993 Repair Guide

Evaporative Emission Control System

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OPERATION



The evaporative emission control system is designed to control the emission of gasoline vapors into the atmosphere. On carbureted engines, the vapors rising from the gasoline in the fuel tank are vented into a separate condensing tank which is located above the fuel tank. There they condense and return to the fuel tank in liquid form when the engine is not running.

When the engine is running, the fuel vapors are sucked directly into the engine through the PCV valve and are burned along with the air/fuel mixture.

Any additional fuel vapors which are not handled by the condensing tank are stored in a charcoal canister. When the engine is running, the charcoal is purged of its stored fuel vapor. On some models, a check valve vents the fuel vapor into the atmosphere if pressure becomes too excessive in the fuel tank.

The system on the carbureted models consists of a charcoal canister, check and cut valve, purge control valves, evaporator shutter valve in air cleaner.

On the pickup and MPV with fuel injection

, the system takes fuel vapor that is generated in the fuel tank and stores it in the charcoal canister when the engine is not running. This fuel vapor remains in the canister until the engine is started at which time the fuel vapor is drawn into the dynamic chamber and burned. The system on these models is made up of the charcoal canister, purge control solenoid valves, a three-way check valve, vacuum switch control valve and an electronic control unit.

On the Navajo

, the Evaporative Emission Control System provides a sealed fuel system with the capability to store and condense fuel vapors. The system has three parts: a fill control vent system; a vapor vent and storage system; and a pressure and vacuum relief system (special fill cap). The fill control vent system is a modification to the fuel tank. It uses an air space within the tank which is 10-12% of the tank's volume. The air space is sufficient to provide for the thermal expansion of the fuel. The space also serves as part of the in-tank vapor vent system. The in-tank vent system consists of the air space previously described and a vapor separator assembly. The separator assembly is mounted to the top of the fuel tank and is secured by a cam-lockring, similar to the one which secures the fuel sending unit. Foam material fills the vapor separator assembly. The foam material separates raw fuel and vapors, thus retarding the entrance of fuel into the vapor line.

COMPONENT TESTING



There are several things to check if a malfunction of the evaporative emission control system is suspected.

Leaks may be traced by using an infrared hydrocarbon tester. Run the test probe along the lines an connections. The meter will indicate the presence of a leak by a high hydrocarbon (HC) reading. This method is much more accurate than a visual inspection which would indicate only the presence of a leak large enough to pass liquid.

Leaks may be caused by any of the following, so always check these areas when looking for them:



Defective or worn lines
 
Disconnected or pinched lines
 
Improperly routed lines
 
A defective check valve
 

If it becomes necessary to replace any of the lines used in the evaporative emission control system, use only those hoses which are fuel resistant or are marked EVAP.

If the fuel tank has collapsed, it may be the fault of clogged or pinched vent lines, a defective vapor separator, or a plugged or incorrect check valve.

Carbureted Engines

See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Evaporative emission control system

The EEC system consists of a canister No. 3 purge control valve, water thermo valve, check-and-cut valve, purge solenoid valve and an air vent solenoid valve.

The water thermo valve opens the vacuum passage to the No. 1 and No. 3 purge control valves. The canister incorporates the No. 2 purge control valve (2 way check valve), and the No. 1 purge control valve, which opens the fuel vapor passage between the canister and the intake manifold. The No. 3 purge control valve opens the fuel vapor passage between the canister and the intake manifold when the purge solenoid valve is ON.

Port vacuum is applied to the No. 1 purge control valve while the engine is running and to the No. 3 purge control valve during running or heavy load driving.

The check-and-cut valve vents the vapors to the atmosphere if the evaporative hoses become clogged. It also prevents fuel leakage if the vehicle overturns.

  1. Check the vacuum hose routing. Repair or replace if necessary.
  2.  
  3. Start the engine and allow it to reach normal operating temperature.
  4.  
  5. Disconnect the vacuum hose from the No. 1 purge control valve. Connect a suitable vacuum gauge to the hose.
  6.  
  7. Increase the engine speed to 2500 rpm and check that the vacuum gauge reads more than 5.9 in. Hg. If the required vacuum is not reached, check the thermo valve. Reconnect the vacuum hose to the control valve.
  8.  
  9. Disconnect the vacuum line from the canister. Connect a vacuum gauge to the hose. Check that vacuum is present when engine speed exceeds 1400 rpm.
  10.  
  11. If no vacuum exists, check the purge solenoid valve, No. 3 purge control valve and the 1V terminal on the emission control unit. Reconnect the vacuum hose to the canister.
  12.  
  13. Disconnect the evaporation hose from the evaporation pipe, then connect a suitable hand operated vacuum pump to the evaporation pipe. Operate the hand pump and check that no vacuum is held in the system. If so, examine the check-and-cut valve and the evaporation pipe for clogging.
  14.  

AIR VENT SOLENOID VALVE
  1. Remove the air cleaner assembly.
  2.  
  3. Touch the air vent solenoid on the carburetor.
  4.  
  5. Verify that when the ignition switch is turned ON and OFF, the solenoid clicking is felt and heard.
  6.  
  7. If not click is heard or felt, check for voltage at the solenoid or replace the solenoid.
  8.  

CHECK AND CUT VALVE

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Check and cut valve testing

  1. Remove the valve from its location just before the gas tank. Hold the valve in the horizontal position, otherwise the weight of the valve will cause it to move out of position and close the passage.
  2.  
  3. Connect a vacuum gauge in line to the passage which normally connects to the fuel tank - port A .
  4.  
  5. Blow air into port A and verify that the valve opens at a pressure of 0.78-1.00 psi (5.38-6.89kpa).
  6.  
  7. Remove the vacuum gauge and connect it to the passage to atmosphere - port B .
  8.  
  9. Blow air into port B and verify that the valve opens at a pressure of 0.14-0.71 psi (0.97-4.89kpa).
  10.  
  11. If not as specified, replace the valve.
  12.  

WATER THERMO VALVE
  1. Remove the water thermo valve and immerse the valve in a container of water.
  2.  
  3. Heat the water gradually and observe the temperature. Remember, you are working with hot metal and hot water, take steps to prevent burning yourself. Blow through the valve. If air passes through the valve at 130°F (54°C) or higher, the valve is operating correctly.
  4.  

SLOW FUEL CUT SOLENOID VALVE
  1. Run the engine at idle speed and disconnect the slow fuel cut solenoid valve connector.
  2.  
  3. If the engine stalls, the solenoid valve is operating properly. If the engine does not stall, replace the solenoid valve.
  4.  

NO. 1 PURGE CONTROL VALVE

See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: No. 1 purge control valve testing

  1. Disconnect the vacuum lines from the canister.
  2.  
  3. Blow through port A and verify that the air does not flow.
  4.  
  5. Connect a vacuum pump to the purge control valve.
  6.  
  7. Apply 4.3 in. Hg of vacuum to the purge control valve.
  8.  
  9. Blow air through port B and verify that air does not flow.
  10.  
  11. If not as specified, replace the purge control valve.
  12.  

NO. 2 PURGE CONTROL VALVE

See Figure 4



Click image to see an enlarged view

Fig. Fig. 4: No. 2 purge control valve testing

  1. Disconnect the vacuum hose from the fuel tank to the canister at the canister.
  2.  
  3. Blow air into the canister.
  4.  
  5. Verify that the air flows freely and there are no restrictions.
  6.  
  7. If not as specified, replace the canister.
  8.  

NO. 3 PURGE CONTROL VALVE

See Figure 5



Click image to see an enlarged view

Fig. Fig. 5: No. 3 purge control valve testing

  1. Remove the No. 3 purge control valve.
  2.  
  3. Connect a hand vacuum pump to the thermosensor side of the valve.
  4.  
  5. Blow air through the valve from port A while applying 3-4 in. Hg of vacuum to the valve.
  6.  
  7. Verify that air flows through the valve from port A to port B .
  8.  
  9. If not as specified, replace the No. 3 purge control valve.
  10.  

Pickup and MPV with Fuel Injection

See Figure 6



Click image to see an enlarged view

Fig. Fig. 6: Evaporative emission control system-2.2L and 2.6L fuel injected engines

The EEC system consists of a fuel separator, a fuel vapor valve, a check-and-cut valve, a 2 way check valve, a purge control solenoid valve, the engine control unit and input devices.

The amount of evaporative fumes introduced into and burned by the engine is controlled by the solenoid valve and control unit to correspond to the engine's operating conditions.

PURGE CONTROL SOLENOID VALVE

See Figure 7



Click image to see an enlarged view

Fig. Fig. 7: Purge control solenoid valve-2.6L and 3.0L fuel injected engines

  1. Start the vehicle and warm the engine.
  2.  
  3. Disconnect the vacuum hose (usually white) closest to the wire connector from the solenoid valve.
  4.  
  5. Verify there is no vacuum at the solenoid valve at idle speed.
  6.  
  7. If there is vacuum at the solenoid valve, turn the engine OFF.
  8.  
  9. Disconnect the other vacuum hose and apply air pressure. Verify that no air flows through the valve.
  10.  
  11. Next, supply 12 volts to the terminals of the solenoid. Apply air pressure and verify that air does flow through the valve.
  12.  
  13. If not as specified, replace the solenoid valve.
  14.  

FUEL SEPARATOR

The fuel separator is not serviceable and should be checked periodically for damage or leaking. Replace the separator if damage or leaking is evident. The separator is located on the right rear wheelhouse on MPVs, and above the fuel tank on pickup models.

CHECK AND CUT VALVE

See Figure 2

  1. Remove the valve from its location just before the gas tank. Hold the valve in the horizontal position, otherwise the weight of the valve will cause it to move out of position and close the passage.
  2.  
  3. Connect a vacuum gauge in line to the passage which normally connects to the fuel tank - port A .
  4.  
  5. Blow air into port A and verify that the valve opens at a pressure of 0.78-1.00 psi (5.38-6.89kpa).
  6.  
  7. Remove the vacuum gauge and connect it to the passage to atmosphere - port B .
  8.  
  9. Blow air into port B and verify that the valve opens at a pressure of 0.14-0.71 psi (0.96-4.89kpa).
  10.  
  11. If not as specified, replace the valve.
  12.  

2 WAY CHECK VALVE

See Figure 8



Click image to see an enlarged view

Fig. Fig. 8: 2 way check valve testing

The 2 way check valve is not serviceable and should be replaced if damage or leaking is evident.

  1. Remove the valve and blow through from port A and check that air flows.
  2.  
  3. Blow through from the opposite side port and check that air does not flow through. Replace the valve as required.
  4.  

Navajo

See Figure 9



Click image to see an enlarged view

Fig. Fig. 9: Evaporative canister

Other than a visual check to determine that none of the vapor lines are broken, there is no test for this equipment.

The only maintenance on the evaporative system is to periodically check all hoses and connections for leaks and deterioration. Replace any hoses which are found to be damaged in any way. Under normal circumstances, the charcoal canister is expected to last the life of the vehicle, but it should be periodically inspected for any damage or contamination by raw gasoline. Replace any gasoline soaked canister found. Refer to the illustrations for canister mounting and evaporative hose routing on the various engines. Filler cap damage or contamination that clogs the pressure/vacuum valve may result in deformation of the fuel tank.

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Mark and disconnect the vapor hoses from the canister assembly.
  4.  
  5. Remove the screw securing the canister to the bracket or fender apron.
  6.  
  7. Lift up on the canister assembly to disengage the tab on the back side and remove the canister.
  8.  
  9. Installation is the reverse of the service removal procedure. Always install vapor hose in correct location.
  10.  

To disconnect a vapor hose from any component securely grip component with one hand and vapor hose with the other hand as close as possible to connection. Sharply twist hose along its axis to break the connection. No adhesive is used to make hose connections during vehicle assembly, but aging of the connections causes a temporary bond to exist.

If the connection is stubborn and the above method does not work, grip the hose with a pair of small pliers directly over the joint and twist again. Remove the vapor hose from the component.

 
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