Honda Civic/CRX/del Sol 1984-1995 Repair Guide

Additional Exhaust Emission Controls

Print

CARBURETED VEHICLES



Mixture Control System

See Figure 1

The anti-afterburn valve and air valve let fresh air into the intake manifold when the manifold vacuum suddenly increases; such as during deceleration.



Click image to see an enlarged view

Fig. Fig. 1: Mixture control system diagram-carbureted engine

ANTI-AFTERBURN VALVE

When manifold vacuum suddenly increases (i.e. sudden deceleration), the diaphragm/valve unit is pulled downward. Air flow from the air chamber to the sensing chamber is restricted by an orifice, creating a pressure differential on the diaphragm, which holds the valve open. This unbalanced condition lasts for a few seconds until the pressure in both chambers is equalized by air entering through the orifice, then the spring pushes the diaphragm up, closing the valve.

ANTI-AFTERBURN CONTROL SOLENOID VALVE

The anti-afterburn control solenoid valve is designed to cut off manifold vacuum flow to the top side of the anti-afterburn valve diaphragm.

On Manual transaxle cars, when the vehicle speed is below 10 mph, the anti-afterburn control solenoid valve opens and the anti-afterburn valve does not open because there is no vacuum difference on both sides of the diaphragm.

On automatic transaxle cars, the anti-afterburn control solenoid valve is off for four seconds after cranking the engine. Thereafter, it is on to activate the anti-afterburn valve.

AIR VALVE

When manifold vacuum is above the set vacuum of the control switch, the switch is open so manifold vacuum is applied to the air valve to open the air passage.

AIR CONTROL SOLENOID VALVE (1.3L ONLY)

The air control solenoid valve is designed to bleed manifold vacuum to the atmosphere. When the solenoid valve is opened, it takes a higher level of manifold vacuum to open the control switch.

VACUUM CONTROL VALVE (1.3L HI ALT (ALL); 1.5L 2WD M/T (ALL); 49 STATE (HI ALT)

When the engine coolant temperature exceeds the set temperature of thermovalve A and manifold vacuum suddenly increases, the diaphragm/valve is opened, which allows manifold vacuum into the air valve.

Air Injection System

See Figures 2 and 3

AIR SUPPLY-TO-EXHAUST MANIFOLD

This system makes use of vacuum pulses in the exhaust manifold to draw air from the air cleaner to the exhaust manifold to promote oxidation of hydrocarbons.

The control unit energizes the air suction control solenoid valve to apply manifold vacuum to the air suction cut-off diaphragm valve, which opens the secondary air passage. When negative pressure, created by exhaust pulses, opens the air suction reed valve, fresh air pours into the exhaust manifold.

Air bleed valve B is designed to cut off manifold vacuum flow to the air suction cut-off diaphragm. When air bleed valve B opens fresh air does not pour into the exhaust manifold because the air suction cut-off diaphragm valve closes the secondary air passage. The air chamber acts as silencer to reduce exhaust noise.



Click image to see an enlarged view

Fig. Fig. 2: Air injection system-carbureted engine



Click image to see an enlarged view

Fig. Fig. 3: Auxiliary carburetor air supply system-carbureted engine

Auxiliary Carburetor Air Supply System

When the engine coolant temperature is below the set temperature of thermovalve C, fresh air pours into the auxiliary intake manifold to prevent an overly-rich mixture.

During gear shifting or deceleration, the anti-afterburn valve senses the change in intake manifold vacuum, and provides fresh air into the intake manifold.

Under such conditions, fresh air is also supplied from the anti-afterburn valve into the intake ports of the auxiliary carburetor throat through check valve G in order to prevent an incombustible mixture in the auxiliary combustion chamber.

Feedback Control System

The Feedback Control System maintains the proper air/fuel mixture ratio by allowing air into the intake manifold, as is necessary, to adjust a temporarily fuel-rich condition. This system is made up of two subsystems; the X-system and the M-system.

The X-system consists of air control valve B, frequency solenoid valve B, feedback control solenoid valve, check valve B, surge tanks A and B, and control unit. When frequency solenoid valve B and feedback control solenoid valve are activated by the control unit, manifold vacuum is applied to air control valve B. When air control valve B opens, it allows the correct amount of air to be fed into the intake manifold.

Surge tank A acts as a vacuum reservoir while surge tank B dampens the vacuum pulses so the relatively steady vacuum is applied to air control valve B.

The M-system consists of air control valve A, frequency solenoid valve A and control unit. When frequency solenoid valve A is opened by control unit, air control valve A, which has been already opened by vacuum from the carburetor port, feeds the correct amount of air into the intake manifold. The amount of air is proportional to intake air volume.

COMPONENT TESTING



Intake Air Temperature Control System (Engine Cold)

See Figure 4

  1. Inspect for loose, disconnected, or deteriorated vacuum hoses and replace as necessary.
  2.  
  3. Remove the air cleaner cover and element.
  4.  
  5. With the transmission in Neutral and the blue distributor disconnected, engage the starter motor for approximately two (2) seconds. Manifold vacuum to the vacuum motor should completely raise the air control valve door. Once opened, the valve door should stay open unless there is a leak in the system.
  6.  
  7. If the valve door does not open, check the intake manifold port by passing a No. 78 - 0.016 in. (0.4mm) diameter - drill or compressed air through the orifice in the manifold.
  8.  
  9. If the valve door still does not open, proceed to the following steps:
    1. Vacuum Motor Test: Disconnect the vacuum line from the vacuum motor inlet pipe. Fully open the air control valve door; block the vacuum motor inlet pipe, then release the door. If the door does not remain open, the vacuum motor is defective. Replace as necessary and repeat Steps 1-3.
    2.  
    3. Air Bleed Valve Test: Unblock the inlet pipe and make sure that the valve door fully closes without sticking or binding. Reconnect the vacuum line to the vacuum motor inlet pipe. Connect a vacuum source (for example, hand vacuum pump) to the manifold vacuum line (disconnect at the intake manifold fixed orifice) and draw enough vacuum to fully open the valve door. If the valve door closes with the manifold vacuum line plugged (by the vacuum pump), then vacuum is leaking through the air bleed valve. Replace as necessary and repeat Steps 1-3.
    4.  

  10.  


WARNING
Never force the air bleed valve (bi-metal strip) on or off its valve seat. The bimetallic strip and the valve seat may be damaged.

  1. After completing the above steps, replace the air cleaner element and cover and fit a vacuum gauge into the line leading to the vacuum motor.
  2.  
  3. Start the engine and raise the idle to 1500-2000 rpm. As the engine warms, the vacuum gauge reading should drop to zero.
  4.  

Allow sufficient time for the engine to reach normal operating temperature - when the cooling fan cycles on and off.

If the reading does not drop to zero before the engine reaches normal operating temperature, the air bleed valve is defective and must be replaced. Repeat Step 3 as a final check.



Click image to see an enlarged view

Fig. Fig. 4: Feedback control system-carbureted engines

Temperature and Transaxle Controlled Spark Advance (Engine Cold)

See Figures 5 and 6

  1. Check for loose, disconnected or deteriorated vacuum hoses and replace (if necessary).
  2.  
  3. Check the coolant temperature sensor switch for proper operation with an ohmmeter or 12V light. The switch should normally be open (no continuity across the switch terminals) when the coolant temperature is below approximately 120°F (49°C). If the switch is closed (continuity across the terminals), replace the switch and repeat the check.
  4.  
  5. On manual transaxle models, check the transmission sensor switch. The switch should be open (no continuity across the connections) when 4th gear is selected, and closed (continuity across the connections) in all other gear positions. Replace if necessary and repeat the check.
  6.  



Click image to see an enlarged view

Fig. Fig. 5: Intake air control system components-carbureted engines



Click image to see an enlarged view

Fig. Fig. 6: Testing the vacuum advance diaphragm-disconnect vacuum hose No. 2 to connect the vacuum pump

  1. Remove the spark control vacuum tube, leading between the spark advance/retard unit and the solenoid valve, and connect a vacuum gauge to the now vacant hole in the solenoid valve, according to the diagram.
  2.  
  3. Start the engine and raise the idle to 2000 rpm. With a cold engine, the vacuum gauge should read approximately 3 in. Hg or more. As the coolant temperature reaches 120°F (49°C), the vacuum reading should drop to 0. On manual transaxle models, vacuum should return when 4th gear is selected (transmission switch is opened). If this is not the case, proceed to the following steps:
  4.  

If the engine is warm from the previous test, disconnect the coolant temperature switch wires when making the following tests.

  1. If vacuum is not initially available, disconnect the vacuum signal line from the charcoal canister and plug the open end, which will block a possible vacuum leak from the idle cut-off valve of the canister. With the line plugged, again check for vacuum at 2000 rpm. If vacuum is now available, reconnect the vacuum signal line and check the canister for vacuum leaks. (Refer to the Evaporative Emission Control System check.) If vacuum is still not available, stop the engine and disconnect the vacuum line from the solenoid valve (the line between the solenoid valve and the manifold T-joint) and insert a vacuum gauge in the line. If vacuum is not available, the vacuum port is blocked. Clear the port with compressed air and repeat the test sequence beginning with Step 3.
  2.  

  1. If vacuum is available in Step 5 after the engine is warm and in all ranges of the automatic transaxle and in 1st, 2nd and 3rd of the manual transaxle, stop the engine and check for electrical continuity between the terminals of the coolant temperature sensor:
    1. If there is no continuity (engine is warm), replace the temperature sensor switch and recheck for continuity.
    2.  
    3. If there is continuity, check the battery voltage to the vacuum solenoid. If no voltage is available (ignition switch ON ), check the wiring, fuses and connections.
    4.  
    5. If there is battery voltage and the temperature sensor is operating correctly, check connections and/or replace the solenoid valve.
    6.  

  2.  

After completing the above steps, repeat test procedure beginning with Step 4.

Feedback Control System

See Figures 7 and 8

These tests require the use of two hand held vacuum pumps. These must be designed to provide either air pressure or vacuum.



Click image to see an enlarged view

Fig. Fig. 7: Connecting a vacuum pump to the air control valve



Click image to see an enlarged view

Fig. Fig. 8: Use two vacuum pumps to test air control valve B

  1. Disconnect the air suction hose at the vacuum hose manifold. Tee in a vacuum pump as shown in the illustration. Hook up the pump so as to apply pressure. Then, use the vacuum pump to attempt to force air pressure into the system. If air does not flow, proceed to step 2. If it does, proceed to 2a.
    1. If air flows into the system, remove the air box cover and then pinch off the vacuum hose leading to frequency solenoid valve A. Then, blow air through the hose. If air flows, replace air control valve B and then recheck that air does not flow. If air does not flow, replace the frequency solenoid valve A and retest as in Step 1.
    2.  

  2.  
  3. Disconnect vacuum hose No. 24 at surge tank B. Connect the vacuum pump to the end of this hose so as to apply pressure. Then, disconnect the hose leading from Air Control Valve B and frequency solenoid valve A. Connect the hand pump so as to apply pressure. Apply vacuum at hose #24 and blow air into the other hose (the B-valve side of the Air Control Valve). Air should flow. If it does, proceed to Step 3. If not, proceed to 2a.
    1. Replace air control valve B and then retest the system to make sure air does flow.
    2.  

  4.  
  5. Jumper battery voltage (from the + terminal) to the green/white connector of connector box #2 (see illustration). Blow air into the vacuum hose going to frequency valve A. If air flows, the valve is okay and you should proceed to Step 4. If not, proceed to Step 3a.
    1. If air does not flow, disconnect the hose leading from frequency solenoid valve A to air control valve A and check for air flow with the pump in operation. If air flows, replace control valve A and then retest to make sure the system now works. If air does not flow, replace frequency solenoid valve A and re-test to make sure the system now works.
    2.  

  6.  
  7. Disconnect vacuum hose #29 at the vacuum hose manifold and connect the vacuum pump to the open end. Apply vacuum to the open end and blow air into the air suction hose leading to Control Valve A. When there is vacuum applied via the pump, air should flow without resistance. When vacuum is released, air should flow into the system only with significant resistance; that is, pressure should build up on the gauge of the pump supplying pressure and then be released only gradually. If this occurs, reconnect the air suction hose and hose #29 and then go on to Step 5. If there is no such change in resistance, replace air control valve A and then repeat the test.
  8.  
  9. Jumper battery voltage from the battery (+) terminal to the frequency solenoid valve B. Disconnect the vacuum hose #23 from surge tank B and connect a vacuum pump to it. Then, apply vacuum. Vacuum should build up on the pressure gauge. If there is vacuum, go to Step 6. If not, pinch the hose leading from the frequency solenoid valve B to the constant vacuum valve. Then, repeat the test. If there is now vacuum, replace the constant vacuum valve and then retest to make sure the system is repaired. If there is still no vacuum, replace the frequency solenoid valve B and repeat the test to make sure the system is repaired.
  10.  
  11. Leaving the vacuum pump hooked up, disconnect the jumper wire leading to frequency solenoid valve B. Make sure there is still vacuum in the system. Vacuum should disappear when the wire is disconnected. If it does disappear, reconnect vacuum hose #23 and go on to Step 7. If it does not disappear, replace solenoid valve B and retest to make sure it now disappears.
  12.  
  13. Remove the cover of control box #2 and disconnect the hose connecting the constant vacuum valve and frequency solenoid valve B from its connection within the box. Then, connect a vacuum pump to the open end of the hose. Now, start the engine, allow it to idle, and measure the vacuum with a gauge. It should stabilize in the range 6-11 in.Hg (manual transaxle) vehicles and 2-7 in.Hg (automatic transaxle). If vacuum stabilizes in this range, the constant vacuum valve is okay, and you should reconnect the hose. If not, replace the constant vacuum valve, and then retest to make sure you have corrected the malfunction.
  14.  

 
label.common.footer.alt.autozoneLogo