Honda Accord/Prelude 1984-1995 Repair Guide

Air/Fuel Mixture

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Fuel injected vehicles do not allow the manual adjustment of the air/fuel mixture. The engine control unit or ECU is in charge of that and controls the function of the fuel injectors according to the electric signals sent to it by a host of sensors and monitors. If a fuel injected engine suffers an emission related problem, the sensors and computer-controlled output components must be tested and repaired.

On carbureted engines, this procedure is used to adjust the base idle after carburetor disassembly or repair. In general, the mixture is preset at the factory and should not be altered or adjusted casually. Federal law requires the manufacturer to insert tamper-proof plugs or other devices to keep the uninformed out of the carburetor. These procedures require a fair amount of disassembly, including the removal of the carburetor in some cases. If you are anticipating performing a mixture adjustment solely as part of a maintenance program, don't. The risk of creating more problems outweighs a slight adjustment on an otherwise properly running engine.

The use of the correct tools, in this case a propane enrichment kit, is required for this procedure. Do not begin the procedure if the kit is not available. Make certain the propane bottle is sufficiently full before beginning the procedure.

The mixture may also be determined through the use of an exhaust gas analyzer or emissions tester, but this equipment is rarely available to the home mechanic. If this method is used, you must still gain access to the mixture adjusting screw(s) to perform the adjustments.

ADJUSTMENT



1984-85 Accord and 1986-89 Accord with Manual Transaxles

See Figures 1, 2, 3, 4, 5, 6 and 7

A Keihin 2-barrel carburetor is used on these models.

  1. Place the vehicle in the Park or Neutral. Apply the emergency brake and block the drive wheels. Start the engine and allow it to reach normal operating temperature. The cooling fan(s) should come on at least once.
  2.  
  3. Remove the vacuum hose from the intake air control diaphragm and clamp or plug the hose end.
  4.  



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Fig. Fig. 1: Remove the hose from the intake air diaphragm, then plug it

  1. Connect a suitable tachometer to the engine following the manufacturers instructions.
  2.  
  3. Check the idle speed with all the accessories turned OFF. If necessary, adjust the idle speed by turning the throttle stop screw.
  4.  
  5. Disconnect the air cleaner intake tube from the air duct on the radiator bulkhead.
  6.  
  7. Insert the hose from the propane kit into the intake tube approximately 4 inches (10 cm).
  8.  


CAUTION
Propane is a flammable gas. Observe "no smoking/no open flame" precautions. Have a Class B-C (dry powder) fire extinguisher within arm's reach at all times.

  1. With the engine idling, depress the lock button on top of the propane device, then slowly open the propane control valve to obtain the maximum engine speed. The engine speed should increase as the percentage of propane injected goes up.
  2.  



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Fig. Fig. 2: Injecting propane into the air stream should cause the idle to increase, then decrease. Adjust the flow to hold maximum idle speed

Open the propane control valve slowly; a sudden burst of propane may cause the engine to stall.

  1. The engine idle speed should increase as follows:

    1984-85 Accord w/MT-75-125 rpm
     
    1984-85 Accord w/AT-30-70 rpm
     
    1986 Accord w/MT-15-55 rpm
     
    1987-89 Accord w/MT-30-70 rpm
     

  2.  

  1. If the engine speed increases according to specifications, remove the propane kit, all test equipment and reconnect all disconnected vacuum hoses. If the engine speed fails to increase as specified, continue with the following steps. Switch the ignition OFF .
  2.  
  3. Disconnect the vacuum hose to the fast idle unloader. Pull the throttle cable out of the bracket.
  4.  
  5. Remove the carburetor nuts, washers and bolts securing the steel tubing vacuum manifold. Lift the carburetor clear of the studs, then tilt it backward to obtain the access to the throttle controller bracket screws.
  6.  
  7. Remove the throttle controller bracket. Remove the mixture adjusting screw hole cap from the throttle controller bracket, then reinstall the bracket. With the plug removed, the adjusting screw can now be reached from the outside of the carburetor body with the carburetor in place.
  8.  



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Fig. Fig. 3: Remove the screw securing the throttle control bracket; 1984 Accord shown



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Fig. Fig. 4: The hole cap can be removed after the bracket is removed; 1984-85 Accord shown



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Fig. Fig. 5: Removing the screw securing the throttle control bracket; 1987 Accord shown



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Fig. Fig. 6: The hole cap can be removed after the bracket is removed

  1. Reinstall the carburetor, reconnect the vacuum hose to the fast idle unloader. Reinstall the air cleaner.
  2.  
  3. Start the engine and let it warm up again to normal operating temperature.
  4.  
  5. Remove the vacuum hose from the intake air control diaphragm and clamp or plug the hose end. Reinstall the propane enrichment kit and recheck the maximum propane enrichment rpm.
  6.  
  7. If the propane enriched speed is too low, the mixture is rich. Turn the mixture screw a 1 / 4 turn clockwise and recheck.
  8.  
  9. If the propane enriched speed is too high, the mixture is lean. Turn the mixture screw a 1 / 4 turn counterclockwise and recheck.
  10.  
  11. Close the propane control valve and recheck the idle speed. Be sure to run the engine at 2500 rpm for 10 seconds to stabilize the idle condition.
  12.  
  13. If the engine speed is set to specifications, remove the propane enrichment kit, all test equipment and reconnect all vacuum hoses and the air cleaner intake tube.
  14.  
  15. If the engine speed is not set to specifications, adjust by turning the throttle stop screw. Now repeat the propane enriched speed checks. Once again, check the idle speed and adjust if necessary, by turning the idle control screw.
  16.  
  17. If equipped with air conditioning, make a second check with the air conditioning engaged. Adjust the speed if necessary by turning the adjusting screw on the idle boost diaphragm.
  18.  



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Fig. Fig. 7: With the air conditioning operating, adjust the idle at screw B

Some 1984 Accord models may develop a stalling problem at idle. The probable cause of this stalling is a sticking slow mixture cut-off solenoid. If this is the case, the solenoid should be removed and replaced with the updated type of solenoid. Additionally, various cold starting and driveability problems on these cars were cured through the addition of assorted "cold-start" kits from Honda. Consult your dealer's service department for details.

1986-89 Accord with Automatic Transaxles

See Figures 8, 9, 10, 11, 12 and 13

A Keihin 2-barrel carburetor is used on these models.

  1. Place the vehicle in Park or Neutral, then apply the emergency brake and block the drive wheels. Start the engine and allow it to reach normal operating temperature. The cooling fan(s) should come on at least once.
  2.  
  3. Remove vacuum hose from the intake air control diaphragm and clamp or plug the hose end.
  4.  
  5. Connect a suitable tachometer to the engine following the manufacturer's instructions.
  6.  
  7. Remove air filter from frequency solenoid valve "C", then plug the opening in solenoid valve.
  8.  



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Fig. Fig. 8: For vehicles with automatic transaxles, plug the opening in the frequency solenoid valve after the filter is removed

  1. With no engine load, lower the idle speed as much as possible by turning the throttle stop screw.
  2.  



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Fig. Fig. 9: Throttle stop screw for mechanical idle adjustment

  1. Adjust the idle speed to 550-650 rpm (580-680 rpm on 1987-89 models) by turning the idle control screw.
  2.  



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Fig. Fig. 10: Idle control screw location

  1. With headlights on, rear defroster on and the heater blower set to maximum, adjust the idle speed by turning adjusting screw "A." Idle should be 550-650 rpm on 1986 models and 650-750 rpm on 1987-89 models.
  2.  



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Fig. Fig. 11: Location of adjusting screw A

  1. If equipped with air conditioning, adjust the idle speed to 650-750 rpm by turning adjusting screw "B" with air conditioning on.
  2.  



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Fig. Fig. 12: Location of adjusting screw B

  1. With no engine load, remove the inside vacuum hose from the idle boost throttle controller, then plug the hose.
  2.  
  3. Adjust the idle speed to 650-750 rpm (600-700 rpm at high altitude) by turning throttle stop screw.
  4.  
  5. Disconnect the hose from frequency solenoid valve "A" and connect to air control valve "A."
  6.  



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Fig. Fig. 13: Disconnect the hose from the frequency solenoid valve A, then connect it to the control valve

  1. Disconnect the air cleaner intake tube from the air duct on the radiator bulkhead.
  2.  
  3. Insert the hose from the propane kit into the intake tube approximately 4 inches (10 cm).
  4.  


CAUTION
Propane is a flammable gas. Observe "no smoking/no open flame" precautions. Have a Class B-C (dry powder) fire extinguisher within arm's reach at all times.

  1. With the engine idling, depress the lock button on top of the propane device, then slowly open the propane control valve to obtain the maximum engine speed. The engine speed should increase as the percentage of propane injected goes up.
  2.  

Open the propane control valve slowly; a sudden burst of propane may cause the engine to stall.

  1. The engine idle speed should increase 100-170 rpm.
  2.  
  3. If the engine speed increases according to specifications, remove the propane kit, all test equipment and reconnect all disconnected vacuum hoses. If the engine speed fails to increase as specified, continue with the following steps. Switch the ignition OFF .
  4.  
  5. Disconnect the vacuum hose to the fast idle unloader. Pull the throttle cable out of the bracket.
  6.  
  7. Remove the carburetor nuts, washers and bolts securing the steel tubing vacuum manifold. Lift the carburetor clear of the studs, then tilt it backward to obtain the access to the throttle controller bracket screws.
  8.  
  9. Remove the throttle controller bracket. Remove the mixture adjusting screw hole cap from the throttle controller bracket, then reinstall the bracket. With the plug removed, the adjusting screw can now be reached from the outside of the carburetor body with the carburetor in place.
  10.  
  11. Reinstall the carburetor, reconnect the vacuum hose to the fast idle unloader. Reinstall the air cleaner.
  12.  
  13. Start the engine and let it warm up again to normal operating temperature.
  14.  
  15. Remove the vacuum hose from the intake air control diaphragm and clamp or plug the hose end. Reinstall the propane enrichment kit and recheck the maximum propane enrichment rpm.
  16.  
  17. If the propane enriched speed is too low, the mixture is rich. Turn the mixture screw a 1 / 4 turn clockwise and recheck.
  18.  
  19. If the propane enriched speed is too high, the mixture is lean. Turn the mixture screw a 1 / 4 turn counterclockwise and recheck.
  20.  
  21. Close the propane control valve and recheck the idle speed. Be sure to run the engine at 2500 rpm for 10 seconds to stabilize the idle condition.
  22.  
  23. If the engine speed is set to specifications, remove the propane enrichment kit, all test equipment and reconnect all vacuum hoses and the air cleaner intake tube.
  24.  
  25. If the engine speed is not set to specifications, adjust by turning the throttle stop screw. Now repeat the propane enriched speed checks.
  26.  
  27. Stop the engine. Close the propane control valve, remove all plugs and reconnect all the hoses.
  28.  
  29. Restart the engine and recheck idle speed.
  30.  

Raise the engine speed to 2500 rpm 2 or 3 times in 10 seconds, and then check idle speed. Idle speed should be 650-750 rpm on 1986 models and 680-780 rpm on 1987-89 models.

  1. Recheck the idle speed with headlights, heater blower and rear window defroster ON. Idle speed should be 650-750 rpm.
  2.  
  3. Recheck the idle speed with automatic transmission lever in gear. Idle speed should be 650-750 rpm.
  4.  
  5. Recheck the idle speed with air conditioning ON and with the shift lever in Park or Neutral position. Idle speed should be 650-750 rpm.
  6.  
  7. Recheck idle speed with air conditioning ON and in gear. Idle should be 700-800 rpm.
  8.  
  9. If the idle does not reach the specified idle speeds, inspect the idle control system.
  10.  

Keihin Dual Sidedraft Carburetors 1984-90 Prelude

See Figures 14, 15, 16, 17, 18, 19, 20, 21, 22 and 23

Check that the carburetors are synchronized properly before making idle speed and mixture inspection (see Fuel System .) It will also be necessary to remove the ECU fuse from the fuse box for at least 10 seconds to reset the control unit after this procedure is complete.

  1. Start engine and warm up to normal operating temperature. The cooling fans should come on at least once.
  2.  
  3. Remove the vacuum hose from intake air control diaphragm and clamp or plug the hose end.
  4.  

All wires and hoses should be labeled at the time of removal. The amount of time saved during reassembly makes the extra effort well worthwhile.

  1. Connect a tachometer. Check that the fast idle lever is not seated against the fast idle cam. If the fast idle lever is seated against the fast idle cam, it may be necessary to replace the left carburetor.
  2.  



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Fig. Fig. 14: The fast idle cam must not be engaged during propane enrichment testing

  1. Check the idle speed with all accessories turned OFF. Idle speed should be 750-850 rpm (700-750 rpm on automatic transaxles in gear). Adjust the idle speed, if necessary, by turning the throttle stop screw.
  2.  



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Fig. Fig. 15: Prelude throttle stop screw

If the idle speed is excessively high, check the throttle control.

  1. On 1987 automatic transmission cars only, unplug the wiring connector from frequency solenoid valve "A" and use jumper wires to connect the valve to 12 volts. On all other vehicles, unplug the two prong connector from the Electronic Air Control Valve (EACV), disconnect the hose from the vacuum hose manifold and cap the hose end.
  2.  



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Fig. Fig. 16: On 1988-90 Preludes, disconnect the hose from the manifold, then plug the end



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Fig. Fig. 17: On 1984-86 automatic transaxle vehicles, disconnect the hoses and connect the lower hose to air control valve A



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Fig. Fig. 18: Automatic 1987 Preludes require the frequency valve to be jumpered to 12 volts

  1. Unplug the vacuum tubes and connect the lower hose to air control valve "A." Disconnect the vacuum hose from the air conditioning idle boost throttle controller. Disconnect the air cleaner intake tube from the air intake duct.
  2.  
  3. Insert propane enrichment hose into the opening of intake tube about 4 inches (10 cm).
  4.  


CAUTION
Propane is a flammable gas. Observe "no smoking/no open flame" precautions. Have a Class B-C (dry powder) fire extinguisher within arm's reach at all times.

  1. With the engine idling, depress the lock button on top of the propane device, then slowly open propane control valve to obtain maximum engine speed. Engine speed should increase as percentage of propane injected goes up.
  2.  

Open the propane control valve slowly. A sudden burst of propane may stall the engine.

  1. Propane enrichment maximum rpm:

    1984-86 w/MT-20-70 rpm.
     
    1984-86 w/AT-85-135 rpm (in D3 or D4).
     
    1987 w/MT-45-85 rpm.
     
    1987 w/AT-105-155 rpm (in D3 or D4).
     
    1988-90 w/MT-150-190 rpm.
     
    1988-90 w/AT-40-60 rpm.
     

  2.  

  1. If the engine speed change is proper, the procedure is complete. Disconnect the test equipment and reassemble the disconnected lines and hoses. If engine speed does not increase per specification, the mixture must be adjusted. On 1984-87 Preludes, remove the carburetors. On later cars, the plugs may be removed without removing the carburetors.
    1. Place a drill stop on a drill bit so that only 1 / 8 in. (3mm) of the bit is exposed. Drill through the center of each mixture screw hole plug.
    2.  

  2.  

If drilled deeper than this measurement, damage to mixture adjusting screw may result from the bit.

    1. Screw a 5mm sheet metal screw into hole plugs.
    2.  
    3. Grab the screw head with a pair of pliers and remove the hole plugs.
    4.  
    5. If applicable, reinstall the carburetors.
    6.  

  1. Start engine and warm up to normal operating temperature. The cooling fan(s) must come on at least once.
  2.  



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Fig. Fig. 19: On 1984-87 Preludes, the plug must be drilled before removal. A drill stop is required to prevent damage to the screw



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Fig. Fig. 20: Once drilled, remove the plug

  1. Recheck maximum propane enriched rpm. If mixture is rich (engine speed too slow), turn both mixture screws 1 / 4 turn counterclockwise. If mixture is lean (engine speed too high), turn both mixture screws 1 / 4 turn clockwise.
  2.  
  3. Close the propane control valve.
  4.  
  5. Run engine at 2,500 rpm for 10 seconds to stabilize mixture conditions, then check idle speed. Adjust the idle speed, if necessary.
  6.  
  7. On 1984-86 models, remove propane enrichment kit and reconnect the intake air control diaphragm hose. Install new plugs into idle mixture screw holes.
  8.  
  9. On 1987-89 models, disconnect the number "5" vacuum hose from the air suction valve, then plug the hose.
  10.  
  11. On 1987 Preludes, disconnect the upper number "22" vacuum hose from the air leak solenoid valve at the air jet controller support, then plug the end of hose. Connect a vacuum gauge to the solenoid valve.
  12.  



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Fig. Fig. 21: 1987 Preludes require propane testing with vacuum applied to the air leak solenoid



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Fig. Fig. 22: Remove the plug for access to the adjusting screw on 1988-90 Preludes

  1. With the engine idling, depress the lock button on top of the propane device, then slowly open the propane control valve and check vacuum. Vacuum should be available.
  2.  
  3. If no vacuum is present, inspect the air leak solenoid valve and thermovalve "C."
  4.  
  5. Remove the propane enrichment kit and engage the connector.
  6.  

Some 1984-85 Prelude models may experience hesitation on acceleration before the engine has reached normal operating temperature. This can be corrected by installing a cold driveability kit from the manufacturer. This kit holds full vacuum advance to the distributor when the engine is cold.

  1. On 1988-90 vehicles equipped with air conditioning, check the idle with the A/C running at the end of the procedure. If adjustment is necessary, remove the small cap from the adjusting screw and make necessary adjustments.
  2.  



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Fig. Fig. 23: Adjusting screw for idle with air conditioning engaged; 1988-90 Preludes

 
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