Ignition timing is an important part of the tune-up. The 3 basic types of timing lights are available, the neon, the DC and the AC powered. Of the 3 the DC light is the most frequently used by professional mechanics. The bright flash put out by the DC light makes the timing marks stand out on even the brightest of days. Another advantage of the DC light is that you don't need to be near an electrical outlet. Neon lights are available for a few dollars but their weak flash makes it necessary to use them in a fairly dark work area. The 1 neon light lead is attached to the spark plug and the other to the plug wire. The DC light attaches to the spark plug and the wire with an adapter and 2 clips attach to the battery posts for power. The AC unit is similar, except that the power cable is plugged into a house outlet.
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. Basic Ignition timing is controlled by turning the distributor body in the engine. Electronic spark timing is controlled by the Electronic Control Unit (ECU).
Ideally, the air/fuel mixture in the cylinder will be ignited by the spark plug just as the piston passes TDC of the compression stroke. If this happens, the piston will be beginning its downward motion of the power stroke just as the compressed and ignited air/fuel mixture starts to expand. The expansion of the air/fuel mixture then forces the piston down on the power stroke and turns the crankshaft.
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 or after the piston reaches TDC (BTDC or ATDC). 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 has a means to advance the timing of the spark as the engine speed increases. This is accomplished by centrifugal weights within the distributor and a vacuum diaphragm, mounted on the side of the distributor (vehicles without a crank angle sensor). It is necessary to disconnect the vacuum line from the diaphragm when the ignition timing is being set. 1987 and later vehicles are equipped with electronic spark timing to adjust timing as the engine rpm increases.
The timing is best checked with a timing light. This device is connected in series with the No. 1 spark plug. The current which fires the spark plug also causes the timing light to flash. The timing marks consist of a notch or cut out line on the crankshaft pulley and a numbered plate showing crankshaft rotation attached to the front cover. When the engine is running, the timing light is aimed at the marks on the crankshaft pulley and the pointer.
On 1987-88 models, the ECCS system controls the timing there is no mechanical or vacuum advance used in the distributor. Different sensors send signals to the ECU (ECCS control unit) which controls the timing.
On the CA16DE and CA18DE engines do not utilize a conventional distributor and spark plug wires. Instead, they use 4 small ignition coils fitted directly to each spark plug and a crank angle sensor mounted in the front timing belt.
INSPECTION & ADJUSTMENT
Except CA16DE, CA18DE, GA16DE and SR20DE Engines
See Figures 1, 2, 3, 4, 5, 6 and 7
- If equipped with an electronic ignition type distributor, check and/or adjust the reluctor air gap. For further information, refer to Engine Electrical of this information.
- Locate the timing marks on the crankshaft pulley and the front of the engine.
- Clean off the timing marks so that you can see them.
- Use chalk or white paint to color the mark on the crankshaft pulley and the mark on the scale which will indicate the correct timing when aligned with the notch on the crankshaft pulley.
- Attach a tachometer and a timing light to the engine, according to the manufacturer's instructions.
- Disconnect and plug the vacuum line at the distributor vacuum diaphragm, if so equipped. Distributors with a crank angle sensor or camshaft position sensor do not have a vacuum diaphragm. For distributors with a crank angle sensor or camshaft position sensor, proceed to Step 7.
Vehicles which have a crank angle sensor (other than those models with CA16DE, CA18DE, GA16DE and SR20DE engines) include the turbocharged 1984 Pulsar, 1984-88 Pulsar with E16 engine (49 states), 1987-88 models with E16 engine (California and Canada), and 1989-90 Sentra/NX Coupe.
- On the Pulsar E15ET engine (1984 Canadian Turbo), disconnect the Idle Control Valve (ICV) harness connector. On the Pulsar E16 engine (1984 and later, except California and Canada), disconnect the Vacuum Control Modulator (VCM) valve harness connector to adjust the idle speed, then reconnect the harness and make sure that the idle speed is within the proper range.
- Check to make sure that all of the wires clear the fan and then start the engine. Allow the engine to reach normal operating temperature.
- Adjust the idle to the correct setting.
Before checking and/or adjusting the timing, make sure the electrical switches (such as those for the headlights, radiator cooling fan, heater blower and air conditioning) are turned OFF; if equipped with power steering, make sure that the wheels are faced straight ahead.
- Aim the timing light at the timing marks at the front of the engine cover. If the timing marks are aligned when the light flashes, the timing is correct. Turn off the engine, then remove the tachometer and the timing light.
If the timing marks are not aligned, proceed with the following steps:
- Turn off the engine.
- Loosen the distributor lockbolt, just enough, so that the distributor can be turned with a little effort.
- Start the engine. Keep the wires of the timing light clear of the fan.
- With the timing light aimed at the crankshaft pulley and the timing plate on the engine, turn the distributor in the direction of rotor rotation to retard the spark and in the opposite direction to advance the spark. Align the marks on the pulley and the engine scale with the flashes of the timing light.
- Tighten the hold-down bolt. Remove the tachometer and the timing light.
See Figures 4, 8, 9 and 10
The CA16DE and CA18DE engines do not utilize a conventional distributor and high tension wires. Instead they use 4 small ignition coils fitted directly to each spark plug. The ECU controls the coils by means of a crank angle sensor. The crank angle sensor can be found attached to the upper front timing belt cover.
- Run the engine until it reaches normal operating temperature.
- Check that the idle speed is at specifications.
- Disconnect the air duct and both air hoses at the throttle chamber.
- Remove the ornament cover between the camshaft covers. It has 8 screws and says "Twin Cam''.
- Remove the ignition coil at the No. 1 cylinder.
- Connect the No. 1 ignition coil to the No. 1 spark plug with a suitable high tension wire.
- Use an inductive pick-up type timing light and clamp it to the wire connected in Step 6.
- Reconnect the air duct and hoses and then start the engine.
- Check the ignition timing. If not to specifications, turn off the engine and loosen the crank angle sensor mounting bolts slightly.
- Restart the engine and adjust the timing by turning the sensor body slightly until the timing comes into specifications.
See Figures 4, 5 and 6
- Start the engine and allow it to reach normal operating temperature.
- Run the engine at 2000 rpm for 2 minutes and return to idle.
- Turn the engine OFF and disconnect the throttle position sensor harness connector.
- Start the engine and race the engine to 2000 rpm, 3 times.
- Connect a timing light to the No. 1 spark plug wire and battery.
- Loosen the distributor hold-down bolt and adjust the ignition timing to 10 degrees BTDC for the GA16DE and 15 degrees for the SR20DE engines.
- Turn the engine OFF and reconnect the throttle position sensor harness.