Nissan Z - ZX 1970-1988 Repair Guide

Ignition Timing

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GENERAL INFORMATION



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. To do this, the distributor (370-83) has two means of advancing the spark timing as the engine speed increases: a set of centrifugal weights within the distributor and a vacuum diaphragm, mounted on the side of the distributor.

If the ignition is set too far in advance (BTDC), the ignition and expansion of the fuel in the cylinder will occur too soon and tend to force the piston down while it is still traveling up, causing the engine to ping. If the ignition spark is set too far, 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 it's travel. This will result in poor engine performance and lack of power.

The timing marks consist of a notch on the rim of the crankshaft pulley and a scale of degrees attached to the front of the engine. The notch corresponds to the position of the piston in the No. 1 cylinder. A stroboscopic (dynamic) timing light is used, which is hooked into the circuit of the No. 1 cylinder spark plug. Every time the spark plug fires, the timing light flashes, making the mark on the pulley appear to be standing still. The proper timing is indicated when the notch is aligned with the correct number on the scale.

There are three basic types of timing light available:

  1. The first type is a simple neon bulb with two wire connections (one for the spark plug and one for the plug wire, connecting the light in series). This type of light is quite dim and must be held closely to the marks to be seen; it is inexpensive.
  2.  
  3. The second type of light operates from the car battery. Two alligator clips connect to the battery terminals, while a third wire connects to a spark plug with an adapter. This type of light is more expensive and the xenon bulb provides a nice bright flash which can even be seen in sunlight.
  4.  
  5. The third 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.
  6.  

If your vehicle has an electronic ignition, use a timing light with an inductive pickup. This pickup simply clamps onto the No. 1 plug 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 electronic ignition.

INSPECTION AND ADJUSTMENT



Except Turbocharged Models and 384-88 Vehicles

See Figures 1, 2, 3 and 4

Refer to Emissions Controls (Emission Controls) for the procedure to check and adjust phase timing of the dual points or dual pickups in 373-76 models.

If the underhood emissions decal differs from the information given below, always use the information on the decal, as this reflects the latest changes made during production.

  1. On 370-73 models, set the dwell of the breaker points to the proper specification. Refer to the procedure in this section.
  2.  
  3. Locate the timing marks on the crankshaft pulley and the front of the engine.
  4.  
  5. Clean off the timing marks, so that you can see them.
  6.  
  7. Use chalk or white paint to color the mark on the crankshaft pulley and the mark on the scale (which indicates the correct timing when aligned with the notch on the crankshaft pulley).
  8.  
  9. Attach a tachometer to the engine, according to the manufacturer's instructions.
  10.  



Click image to see an enlarged view

Fig. Fig. 1: Crankshaft groove and timing scale-1970-73 models



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Fig. Fig. 2: Timing scale-1974-83 models



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Fig. Fig. 3: Throttle valve switch- 1980 models



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Fig. Fig. 4: Loosen the distributor lockbolt, and turn the distributor body to adjust the timing

  1. Attach a timing light to the engine, according to the manufacturer's instructions.
  2.  
  3. On 370-79 models, leave the vacuum hose connected to the distributor advance vacuum diaphragm.
  4.  
  5. On 380-81 models:
    1. Disconnect the throttle valve switch harness connector.
    2.  
    3. Disconnect and plug the canister purge hose from the intake manifold.
    4.  
    5. Plug the opening in the intake manifold.
    6.  
    7. On 380 49 State models, also disconnect the hose from the air induction pipe and cap the pipe, then disconnect and plug the vacuum advance hose at the distributor.
    8.  

  6.  

The disconnect and plug instructions, for the air induction pipe and the distributor vacuum advance, do not apply to 380 models sold in California or Canada.

  1. On 382-83 models, disconnect and plug the distributor vacuum hose from the distributor vacuum controller. On 383 models, detach the gray harness connector from the distributor.
  2.  
  3. Check that all of the wires clear the fan, pulleys and belts, then start the engine. Allow the engine to reach normal operating temperature.
  4.  


CAUTION
Block the front wheels and set the parking brake. Shift the manual transmission into Neutral or the automatic transmission into Drive. DO NOT stand in front of the car when making adjustments!

  1. Adjust the idle to the correct setting. See the Idle Speed and Mixture procedures later in this section.
  2.  
  3. Aim the timing light at the timing marks. If the marks on the pulley and engine are aligned when the light flashes, the timing is correct. Turn OFF the engine, then remove the tachometer and the timing light.
  4.  
  5. If the marks are not in alignment, proceed with the following steps:
    1. Turn OFF the engine.
    2.  
    3. Loosen the distributor lockbolt just enough so that the distributor can be turned with a little effort.
    4.  
    5. Start the engine. Keep the wires of the timing light clear of the fan.
    6.  
    7. With the timing light aimed at the pulley and the marks on the engine, turn the distributor in the direction of rotor rotation to retard the spark or in the opposite direction of rotor rotation to advance the spark. Align the marks on the pulley and the engine with the flashes of the timing light.
    8.  
    9. Tighten the distributor lockbolt and recheck the timing.
    10.  

  6.  
  7. Reconnect all hoses and electrical connectors.
  8.  
  9. Disconnect the tachometer and timing light.
  10.  

Turbocharged Models and 384-88 Vehicles

See Figures 5, 6 and 7

Ignition timing is controlled by the Central Electronic Control Unit (CECU), and adjusts to the engine operating conditions; that is, as the best ignition timing in each driving condition has been memorized in the unit, the ignition timing is determined by the electric signal calculated in the unit.

The signals used for determining the ignition timing are: cylinder head temperature, engine rpm, engine load, engine crank angle, detonation sensor, etc.



Click image to see an enlarged view

Fig. Fig. 5: Timing Marks-1984-88 models



Click image to see an enlarged view

Fig. Fig. 6: Loosen the distributor lockbolt



Click image to see an enlarged view

Fig. Fig. 7: With a timing light pointed at the marks on the crankshaft pulley, turn the distributor body to adjust the timing

The signal from the CECU is then transmitted to the power transistor of the ignition coil, thereby controlling the ignition timing. If there is engine knocking, a detonation sensor monitors its condition and the signal is transmitted to the CECU. After receiving it, the control unit adjusts the ignition timing to avoid the knocking condition.

Ignition timing is automatically regulated by the control unit and it is usually unnecessary to adjust it. However, the ignition timing can go wrong if the crank angle sensor is misadjusted. Crank angle adjustment should be left to a qualified technician, since it should be preceded by a system test using an ECCS analyzer. (See the explanation given under Electronic Ignition-Turbocharged Engines).

To adjust the timing, proceed as follows:

If the underhood emissions decal differs from the information given below, always use the information on the decal, as this reflects the latest changes made during production.

  1. Locate the timing marks on the crankshaft pulley and the front of the engine.
  2.  
  3. Clean off the timing marks, so that you can see them clearly.
  4.  
  5. Use chalk or white paint to color the mark on the crankshaft pulley and the mark on the scale (which indicates the correct timing when aligned with the notch on the crankshaft pulley).
  6.  
  7. Attach a tachometer to the engine, according to the manufacturer's instructions.
  8.  
  9. Attach a timing light to the engine, according to the manufacturer's instructions.
  10.  
  11. Disconnect the throttle valve switch connector, if equipped.
  12.  
  13. Disconnect and plug the canister purge hose from the intake manifold.
  14.  
  15. Check that all of the wires clear the fan, pulleys and belts, then start the engine. Allow the engine to reach normal operating temperature.
  16.  


CAUTION
Block the front wheels and set the parking brake. Shift the manual transmission into NEUTRAL or the automatic transmission into DRIVE. DO NOT stand in front of the car when making adjustments!

  1. Adjust the idle to the correct setting. See the Idle Speed and Mixture procedures later in this section.
  2.  
  3. Aim the timing light at the timing marks. If the marks on the pulley and engine are aligned when the light flashes, the timing is correct. Turn OFF the engine, then remove the tachometer and the timing light.
  4.  
  5. If the marks are not in alignment, proceed with the following steps:
    1. Turn OFF the engine.
    2.  
    3. Loosen the distributor lockbolt just enough so that the distributor can be turned with a little effort.
    4.  
    5. Start the engine. Keep the wires of the timing light clear of the fan.
    6.  
    7. With the timing light aimed at the pulley and the marks on the engine, turn the distributor in the direction of rotor rotation to retard the spark, or in the opposite direction of rotor rotation to advance the spark. Align the marks on the pulley and the engine with the flashes of the timing light.
    8.  
    9. Tighten the distributor lockbolt and recheck the timing.
    10.  

  6.  
  7. Reconnect all hoses and electrical connectors.
  8.  
  9. Disconnect the tachometer and timing light.
  10.  

 
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