GM Camaro 1982-1992 Repair Guide

Description

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Ignition timing is the measurement, in degrees of crankshaft rotation, of the point at which the spark plugs fire in each of the cylinders. It is measured in degrees before or after Top Dead Center (TDC) of the compression stroke.

Because it takes a fraction of a second for the spark plug to ignite the mixture in the cylinder, the spark plug must fire a little before the piston reaches TDC. Otherwise, the mixture will not be completely ignited as the piston passes TDC and the full power of the explosion will not be used by the engine.

The timing measurement is given in degrees of crankshaft rotation before the piston reaches TDC (BTDC). If the setting for the ignition timing is 5° BTDC, the spark plug must fire 5° before each piston reaches TDC. This only holds true, however, when the engine is at idle speed.

As the engine speed increases, the pistons go faster. The spark plugs have to ignite the fuel even sooner if it is to be completely ignited when the piston reaches TDC.

If the ignition is set too far advanced (BTDC), the ignition and expansion of the fuel in the cylinder will occur too soon and try to force the piston down while it is still traveling up. This causes engine ping. If the ignition spark is set too far retarded, after TDC (ATDC), the piston will have already passed TDC and started on its way down when the fuel is ignited. This will cause the piston to be forced down for only a portion of its travel, resulting in poor engine performance and lack of power.

When timing the engine, the Number 1 plug wire should be used to trigger the timing light. On engines where timing is adjustable, the notch for the No. 1 cylinder is usually scribed across all three edges of the double sheaf pulley. Another notch located 180° away from the No. 1 cylinder notch is scribed only across the center section of the pulley to make it distinguishable from the No. 1 cylinder notch.

There are two basic types of timing lights available. The first type of light operates from the car's battery. Two alligator clips connect to the battery terminals, while a third wire connects to the spark plug with an adapter or to the spark plug wire with an inductive pickup. This type of light is more expensive, but the xenon bulb provides a nice bright flash which can even be seen in sunlight. The second type replaces the battery source with 110-volt house current. Some timing lights have other functions built into them, such as dwell meters, tachometers, or remote starting switches. These are convenient, in that they reduce the tangle of wires under the hood, but may duplicate the functions of tools you already have.

Because this car uses electronic ignition, you should use a timing light with an inductive pickup. This pickup simply clamps around the Number 1 spark plug wire (in this case, the coil wire), eliminating the adapter. It is not susceptible to crossfiring or false triggering, which may occur with a conventional light due to the greater voltages produced by these systems.

ADJUSTMENT



When adjusting the timing, refer to the instructions on the emission control sticker inside the engine compartment. If the instructions on the label disagree with the procedure listed below, follow the instructions on the label.

1982-87 Vehicles
  1. Locate the timing marks on the crankshaft pulley and the front of the engine.
  2.  
  3. Clean off the marks and coat them with white paint or chalk, if necessary, so that they may be seen.
  4.  
  5. Run the engine until it reaches normal operating temperature, then shut off the engine.
  6.  
  7. With the ignition OFF, connect a tachometer to the distributor, and a timing light with an inductive pickup lead to the No. 1 spark plug wire.
  8.  


WARNING
Never pierce a secondary ignition wire in order to connect a timing light. A pierced wire may lead to engine misfiring and driveability problems.

  1. To properly set the ignition timing, the EST must be placed in the bypass mode.
    1. On the 2.5L engine, refer to the emission control label for the procedure.
    2.  

  2.  

If the label is missing or unreadable, contact your Chevrolet dealer for a replacement.

  1. On 2.8L and 5.0L carbureted engines, disconnect the 4-wire EST connector at the distributor. (Fault code 42 may be set in ECM memory, and must be cleared once the procedure is completed). Proceed to Step 7.
  2.  
  3. On 2.8L, 5.0L and 5.7L fuel injected engines, with the engine RUNNING and all accessories off, use a jumper wire to connect diagnostic terminal B and ground terminal A of the 12-terminal Assembly Line Diagnostic Link (ALDL) usually located under the left side of the instrument panel. DO NOT disconnect the 4-wire EST connector at the distributor. Aim the timing light at the timing mark; the line on the balancer or pulley will line up with the timing mark. Increase engine speed and check for timing advance. If the timing still advances with engine speed, perform Step 6. If timing does not advance with engine speed, proceed to Step 7.
  4.  

If timing advances with engine speed, it will be necessary to disconnect the single-wire Set Timing connector. (Fault code 42 may be set in ECM memory, and must be cleared once the procedure is completed).

  1. Remove the jumper wire from the ALDL, and shut off the ignition. Disconnect the Set Timing connector, usually located under the plastic cover above the heater unit, in the engine compartment. (The wire in this connector is normally Tan/Black.)
  2.  
  3. With the engine running and all accessories off, aim the light at the timing mark. The line on the balancer or pulley will line up with the timing mark. If a change in timing is necessary, loosen the hold-down clamp bolt at the base of the distributor. While observing the timing mark, rotate the distributor slightly until the line indicates the correct timing. Use the timing specification on the emission control label in the engine compartment. If this label is missing or damaged, refer to the Tune-Up Specifications chart in this Section.
  4.  
  5. Once the timing is set to specification, tighten the distributor hold-down clamp. Recheck the timing to make sure it did not change while the bolt was being tightened.
  6.  
  7. Remove the jumper wire from the ALDL connector, if applicable, with the engine still running. (Usually, if this is performed before the engine is shut off, no trouble codes will be stored.)
  8.  
  9. Turn the engine OFF, then remove the timing light and tachometer. Reconnect the number 1 spark plug wire, if disconnected.
  10.  
  11. Attach the 4-wire EST connector at the distributor, or reconnect the Set Timing connector, if applicable.
  12.  
  13. Check for fault code 42, and clear, if necessary, by disconnecting the negative battery cable for at least 30 seconds.
  14.  

To prevent ECM damage, the key must be in the OFF position when disconnecting or reconnecting battery cables.

1988-90 Vehicles

See Figure 1

When adjusting the timing, refer to the instructions on the emission control sticker inside the engine compartment. If the instructions on the label disagree with the procedure listed below, follow the instructions on the label.

  1. Locate the timing marks on the crankshaft pulley and the front of the engine.
  2.  
  3. Clean off the marks and coat them with white paint or chalk, so that they may be easily seen.
  4.  
  5. Run the engine until it reaches normal operating temperature, then shut off the engine.
  6.  
  7. With the ignition OFF, connect a tachometer to the distributor, and a timing light with an inductive pickup lead to the No. 1 spark plug wire.
  8.  


WARNING
Never pierce a secondary ignition wire in order to connect a timing light. A pierced wire may lead to engine misfiring and driveability problems.

  1. Start the engine. With the engine running and all accessories off, use a jumper wire to connect diagnostic terminal B and ground terminal A of the 12-terminal Assembly Line Diagnostic Link (ALDL), located under the instrument panel.
  2.  

If jumping the ALDL terminals does not prevent timing advance, the EST bypass wire will have to be disconnected instead.

  1. Aim the timing light at the timing mark. The line on the balancer or pulley will line up with the timing mark. If a change in timing is necessary, loosen the hold-down clamp bolt at the base of the distributor. While observing the timing mark, rotate the distributor slightly until the line indicates the correct timing. Use the timing specification on the emission control label in the engine compartment. If this label is missing or damaged, refer to the Tune-Up Specifications chart in this Section.
  2.  
  3. Once the timing is set to specification, tighten the distributor hold-down clamp. Recheck the timing to make sure it did not change while the bolt was being tightened.
  4.  
  5. With the engine still running, unground the diagnostic terminal. (Ungrounding the diagnostic terminal while the engine is still running will usually prevent trouble codes from being stored.)
  6.  
  7. Turn the engine OFF and remove the timing light and tachometer. Reconnect the number 1 spark plug wire, if disconnected.
  8.  



Click image to see an enlarged view

Fig. Fig. 1: Grounding the diagnostic terminal in order to set ignition timing

1991-92 Vehicles

See Figure 2

When adjusting the timing, refer to the instructions on the emission control sticker inside the engine compartment. If the instructions on the label disagree with the procedure listed below, follow the instructions on the label.

  1. Locate the timing marks on the crankshaft pulley and the front of the engine.
  2.  
  3. Clean off the marks and coat them with white paint or chalk, if necessary, so that they may be seen.
  4.  
  5. Run the engine until it reaches normal operating temperature, then shut off the engine.
  6.  
  7. With the ignition OFF , connect a tachometer to the distributor, and the pickup lead of an inductive timing light to the No. 1 spark plug wire. Connect the timing light power leads according to the manufacturer's instructions.
  8.  


WARNING
Never pierce a secondary ignition wire in order to connect a timing light. A pierced wire may lead to engine misfiring and driveability problems.

  1. Start the engine. With the engine running at normal operating temperature and all accessories OFF, disconnect the EST bypass connector.
  2.  

An ECM code will be set when the EST bypass connector is disconnected.

  1. Aim the timing light at the timing mark. The line on the balancer or pulley will line up with the timing mark. If a change in timing is necessary, loosen the hold-down clamp bolt at the base of the distributor. While observing the timing mark, rotate the distributor slightly until the line indicates the correct timing. Use the timing specification on the emission control label in the engine compartment. If this label is missing or damaged, refer to the Tune-Up Specifications chart in this Section.
  2.  
  3. Tighten the distributor hold-down bolt and recheck the ignition timing to make sure the distributor was not moved when the bolt was tightened.
  4.  
  5. Turn the engine OFF and remove the timing light and tachometer. Reconnect the number 1 spark plug wire, if disconnected.
  6.  
  7. Connect the EST bypass connector, then check for and clear the ECM code by disconnecting the negative battery cable for at least 30 seconds.
  8.  

To prevent ECM damage, the key must be in the OFF position when disconnecting or reconnecting battery cables.



Click image to see an enlarged view

Fig. Fig. 2: EST bypass connector

 
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