Honda Accord/Prelude 1984-1995 Repair Guide

General Information

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Ignition timing is the measurement, in degrees of crankshaft rotation, of the instant the spark plugs in the cylinders fire in relation to the location of the piston.

Ideally, the air/fuel mixture in the cylinder will be ignited and just beginning its rapid expansion as the piston passes Top Dead Center (TDC). If this happens, the piston will be beginning the power stroke just as the compressed and ignited air/fuel mixture starts to expand. The expansion of the air/fuel mixture will force the piston down on the power stroke and turn the crankshaft.

Due to the time it takes for the spark from the plug to completely ignite the mixture in the cylinder, the plug must fire before the piston reaches TDC so the mixture is completely ignited as the piston passes TDC. This measurement is given in degrees of crankshaft rotation before the piston reaches top dead center (BTDC). If the ignition timing setting is 6 degrees BTDC, this means that the spark plug must fire at a time when the piston for that cylinder is 6 degrees BTDC of its compression stroke. However, this only holds true while the engine is at idle.

As you accelerate from idle, the speed of your engine increases. This increase in engine speed means that the pistons are now traveling up and down much faster. Because of this, the spark plugs will have to fire even sooner if the mixture is to be completely ignited as the piston passes TDC. To accomplish this, the system incorporates a means to advance the timing of the spark as engine speed increases.

The mechanical distributor has two means of advancing the ignition timing. One is centrifugal advance and is actuated by weights in the distributor. The other is vacuum advance and is controlled in that large circular "can" on the side of the distributor. Fully electronic systems use the Engine Control Unit (ECU) to control the trigger signal to the coil. The computer can provide for much more accurate spark control than mechanical units.

In addition, some Honda distributors have a vacuum retard mechanism which is contained in the same housing on the side of the distributor as the vacuum advance. Models having two hoses going to the distributor vacuum housing have both vacuum advance and retard. The function of this mechanism is to regulate the timing of the ignition spark under certain engine conditions. This causes more complete burning of the air/fuel mixture in the cylinder and consequently lowers exhaust emissions.

If ignition timing is set too far advanced (BTDC), the ignition and burning of the air/fuel mixture in the cylinder will try to oppose the motion of the piston in the cylinder while it is still traveling upward. This causes engine ping, a sound similar to marbles in a coffee can. If the ignition timing is too far retarded (after, or ATDC), the piston will have already started down on the power stroke when the air/fuel mixture ignites. This will cause the piston to be forced down with much less power. This will result in rough engine performance, lack of power and poor gas mileage.

CHECKING AND ADJUSTING



See Figures 1, 2 and 3


CAUTION
DO NOT grasp the top of the distributor cap while the engine is running, as you might receive a nasty shock. Instead, grab the distributor housing to rotate.



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Fig. Fig. 1: On some engines, the distributor hold-down bolt is covered with a cap

1984-85 Accord and Prelude

The timing marks are located on the flywheel (manual transaxle) or torque converter drive plate (automatic transaxle), with a pointer on the rear of the cylinder block. All are visible from the front right side of the engine compartment after removing a special rubber access plug in the timing mark window. In all cases, the timing is checked with the engine warmed to operating temperature and at idle.

  1. Following the manufacturer's instructions, connect a timing light to the engine. The positive and negative leads connect to their corresponding battery terminals and the spark plug lead to No. 1 spark plug wire.
  2.  
  3. Make sure that all wires are clear of the cooling fan and hot exhaust manifolds.
  4.  
  5. Set the parking brake and block the front wheels. Start the engine. Check that the idle speed is set to specifications.
  6.  
  7. Point the timing light at the timing marks. When the engine is idling, the red mark must align with the pointer. Some timing marks are indicated by 3 lines; the center one must be aligned with the pointer.
  8.  
  9. If necessary to adjust the timing, loosen the distributor hold-down bolt(s) and/or nut and slowly rotate the distributor in the required direction while observing the timing marks.
  10.  
  11. To complete the adjustment operation, tighten the hold-down bolt, taking care not to disturb the adjustment.
  12.  
  13. Switch the ignition OFF . Reinstall the rubber plug in the timing window and remove the timing light.
  14.  



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Fig. Fig. 2: If necessary, loosen the hold-down bolt, then turn the distributor to adjust the timing

1986-89 Accord, 1986-87 Prelude and 1988-90 Carbureted Prelude

The timing marks are located on the flywheel (manual transaxle) or torque converter drive plate (automatic transaxle), with a pointer on the rear of the cylinder block. All are visible from the front right side of the engine compartment after removing a special rubber access plug in the timing mark window. In all cases, the timing is checked with the engine warmed to operating temperature and at idle.

  1. Disconnect the vacuum hoses from the vacuum advance diaphragm, then plug them.
  2.  
  3. Following the manufacturer's instructions, connect a timing light to the engine. The positive and negative leads connect to their corresponding battery terminals and the spark plug lead to No. 1 spark plug wire.
  4.  
  5. Make sure that all wires are clear of the cooling fan and hot exhaust manifolds.
  6.  
  7. Set the parking brake and block the front wheels. Start the engine. Check that the idle speed is set to specifications.
  8.  
  9. Point the timing light at the timing marks. When the engine is idling, the white mark must align with the pointer.
  10.  
  11. If necessary to adjust the timing, loosen the distributor hold-down bolt(s) and/or nut and slowly rotate the distributor in the required direction while observing the timing marks.
  12.  
  13. Unplug, then connect the vacuum hoses to the advance diaphragm.
  14.  
  15. Point the timing light at the timing marks. The red mark must now align with the pointer. If not, the vacuum advance diaphragm and mechanism should be checked.
  16.  
  17. Switch the ignition OFF . Reinstall the rubber plug in the timing window and remove the timing light.
  18.  



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Fig. Fig. 3: Examples of timing marks used on Accords and Preludes

1988-95 Fuel Injected Prelude and 1990-95 Accord

See Figures 4, 5, 6, 7 and 8

The ignition timing on these cars is controlled by the engine computer. It should not be necessary to routinely reset the timing during other maintenance work. On the Accord V-6, the timing is not adjustable. However, ignition timing can be checked using this procedure.

  1. Remove the rubber cap from the timing window on the engine (except on 1994-95 Accords).
  2.  
  3. Start the engine and allow it to warm up. The engine is fully warmed when the cooling fans come on at least once. Switch the ignition OFF .
  4.  
  5. Locate the service check connector and, if applicable, remove the cap. On 1988-91 Preludes, the cap is yellow and the connector is located next to the vacuum control box in the engine compartment. On 1992-95 Preludes, the service connector is located under the middle of the dash. On 1990-93 Accords, the connector is blue and is located behind the right front kick panel, under the dashboard. On 1994-95 Accords, the service connector is located behind the glove box. Use a jumper wire to connect the two terminals of the service connector.
  6.  

  1. Following the manufacturers instructions, connect a timing light to the engine. The positive and negative leads connect to their corresponding battery terminals and the spark plug lead to No. 1 spark plug wire.
  2.  
  3. Make sure that all wires are clear of the cooling fan and hot exhaust manifolds.
  4.  
  5. Set the parking brake and block the front wheels. Start the engine. Check that the idle speed is set to specifications.
  6.  
  7. Point the timing light at the timing marks. On all models except 1994-95 Accords, the marks are on the flywheel. On the 1994-95 Accords, the timing marks are on the crankshaft pulley. When the engine is idling, the red mark must align with the pointer. Some timing marks are indicated by 3 lines; the center one must be aligned with the pointer.
  8.  

  1. If necessary to adjust the timing, loosen the distributor hold-down bolt(s) and/or nut and slowly rotate the distributor in the required direction while observing the timing marks.
  2.  
  3. To complete the adjustment operation, tighten the hold-down bolt, taking care not to disturb the adjustment.
  4.  
  5. Switch the engine OFF . Reinstall the rubber plug in the timing window and remove the timing light. Remove the jumper wire.
  6.  



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Fig. Fig. 4: Service connector on 1988-91 Preludes



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Fig. Fig. 5: Service connector on 1992-95 Preludes



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Fig. Fig. 6: Service connector on 1990-93 Accords



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Fig. Fig. 7: Service connector on 1994-95 Accords



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Fig. Fig. 8: The timing marks on 1994-95 Accords are on the crank pulley

 
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