Honda Accord/Civic/Prelude 1973-1983 Repair Guide

Evaporative Emission Control System

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OPERATION



This system prevents gasoline vapors from escaping into the atmosphere from the fuel tank and carburetor and consists of the components listed in the illustration.

Fuel vapor is stored in the expansion chamber, in the fuel tank and in the vapor line. When the vapor pressure becomes higher than the set pressure of the one-way valve, the valve opens and allows vapor into the charcoal canister. While the engine is stopped or idling, the idle cut-off valve in the canister is closed and the vapor is absorbed by the charcoal.

At partially opened throttle, the idle cut-off valve is opened by manifold vacuum. The vapor that was stored in the charcoal canister and in the vapor line is purged into the intake manifold. Any excessive pressure or vacuum which might build up in the fuel tank is relieved by the two-way valve in the filler cap.

SERVICE



See Figures 1, 2, 3 and 4

Purge Control/Unloader Solenoid Valve
CARBURETED-ENGINE COLD

The coolant temperature must be below the thermosensor(s) set temperature; the thermosensor(s) must have continuity.

  1. Using a Vacuum Pump/Gauge tool No. H/C 058369 or equivalent, disconnect the upper hose (purge control diaphragm valve) from the evaporative canister and connect the hose to the gauge.
  2.  



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Fig. Fig. 1: Purge control/unloader solenoid valve electrical connector



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Fig. Fig. 2: Purge control/unloader solenoid valve electrical connector



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Fig. Fig. 3: Testing charcoal canister with vacuum gauge tool



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Fig. Fig. 4: Thermosensors located on engine block

  1. Start the engine and allow it to idle; there should be no vacuum.
  2.  
  3. If there is vacuum and the vehicle is equipped with a purge control/unloader solenoid valve, perform the following procedures:
    1. Disconnect the purge control/unloader solenoid valve electrical connector.
    2.  
    3. Using an ohmmeter, check for voltage at the connector.
    4.  
    5. If there is voltage, replace the purge control/unloader solenoid valve, then, retest.
    6.  
    7. If there is no voltage, for the 49ST/HI ALT models, inspect the wiring, the fuse and the Thermosensor A, then, retest. If there is no voltage, for the CAL models, inspect the wiring, the fuse and the Thermosensor B, then, retest.
    8.  

  4.  
  5. If there is vacuum and the vehicle is not equipped with a purge control/unloader solenoid valve, replace the thermosensor and retest.
  6.  
  7. To install, reverse the removal procedures.
  8.  

CARBURETED-ENGINE HOT
  1. Using a Vacuum Pump/Gauge tool No. H/C 058369 or equivalent, disconnect the upper hose (purge control diaphragm valve) from the evaporative canister and connect the hose to the gauge.
  2.  
  3. Start the engine and allow it to warm up; there should be vacuum at idle.
  4.  
  5. If there is no vacuum and the vehicle is equipped with a purge control/unloader solenoid valve, perform the following procedures:
    1. Disconnect the purge control/unloader solenoid valve electrical connector.
    2.  
    3. Using an ohmmeter, check for voltage at the connector.
    4.  
    5. If there is voltage, replace the thermosensor, then, retest.
    6.  
    7. If there is no voltage, replace the purge control/unloader solenoid valve, then, retest.
    8.  

  6.  
  7. If there is no vacuum and the vehicle is not equipped with a purge control/unloader solenoid valve, perform the following procedures:
    1. Pinch off the thermosensor-to-air filter hose; there should be vacuum.
    2.  
    3. If no vacuum is present, check the hoses for blockage or leaks.
    4.  

  8.  
  9. To install, reverse the removal procedures.
  10.  

Charcoal Canister

This procedure is to be performed with the engine Hot.

  1. Using a tachometer, connect it to the engine. Start the engine and allow it to reach normal operating temperatures; until the cooling fan turns on.
  2.  
  3. Remove the fuel filler cap.
  4.  
  5. Using a Vacuum Gauge tool No. H/C 081167 or equivalent, disconnect the charcoal canister from the frame and connect the gauge to it.
  6.  
  7. Raise the engine speed to 3,500 rpm; vacuum should appear on the gauge in 1 minute. If vacuum appears, the canister is OK; end of test.
  8.  
  9. If no vacuum appears, perform the following procedures:
    1. Disconnect the vacuum gauge and reinstall the fuel filler cap.
    2.  
    3. Remove the charcoal canister and check for signs of damage or defects.
    4.  
    5. If necessary, replace the canister.
    6.  

  10.  
  11. Stop the engine and disconnect the PVC hose from the charcoal canister.
  12.  
  13. Using a Vacuum Gauge tool No. H/C058369 or equivalent, install it to the purge control solenoid valve (on top of the canister) and perform the following procedures:
    1. Hand pump the vacuum gauge to create vacuum.
    2.  
    3. If the vacuum remains steady, proceed with the next step; if the vacuum drops, replace the canister and retest.
    4.  

  14.  
  15. Reconnect the PCV hose and start the engine; the Purge side vacuum should drop to zero. If the vacuum does not drop to zero, perform the following procedures:
    1. Disconnect the hose from the PCV fitting and check for vacuum at the hose.
    2.  
    3. If vacuum exists, replace the canister and retest.
    4.  
    5. If no vacuum exists, recheck the thermosensor valve operation.
    6.  
    7. If the purge side vacuum drops to zero, connect the vacuum gauge to the purge hose and check for vacuum with the engine speed at 3,500 rpm. If vacuum exists, replace the canister and retest; if no vacuum, inspect the hose and carburetor for blockage.
    8.  

  16.  
  17. Connect the vacuum gauge to the fuel tank hose and check for vacuum. If no vacuum exists, replace the fuel filler cap - test complete. If vacuum exists, replace the canister and retest.
  18.  

 
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