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 has two means to advance the timing of the spark as the engine speed increases: a set of centrifugal weights within the distributor, and a vacuum diaphragm, mounted on the side of the distributor.
On Maxima models a crank angle sensor in the distributor is used. This sensor controls ignition timing and has other engine control functions. There is no vacuum or centrifugal advance all timing settings are controlled by the Electronic Control Unit (ECU).
If the ignition is set too far advanced (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. 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. This will result in poor engine performance and lack of power.
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 number 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. By aiming the timing light at the timing marks, the exact position of the piston within the cylinder can be read, since the stroboscopic flash makes the mark on the pulley appear to be standing still. Proper timing is indicated when the notch is aligned with the correct number on the scale.
There are three basic types of timing lights available. The first 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, but it is inexpensive. The second type of light operates from the car battery. Two alligator clips connect to the battery terminals, while a third wire connects to the spark plug with an adapter. This type of light is more expensive, but the xenon bulb provides a nice bright flash which can even be seen in sunlight. 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.
If your Datsun has electronic ignition, you should use a timing light with an inductive pickup. This pickup simply clamps onto the No. 1 plug wire, eliminating the adapter. It is not prone to crossfiring or false triggering, which may occur with a conventional light, due to the greater voltages produced by electronic ignition.ADJUSTMENT
Single Point and Electronic Ignition Equipped Models
Nissan does not give ignition timing adjustments for 1980 California models or for any 1981 200SXs and for 1981-84 810s and Maxima models. If timing requires adjustment, please refer to the underhood specifications sticker for applicable procedures.
- Set the dwell of the breaker points to the proper specification.
- 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 to the engine.
- Attach a timing light to the engine, according to the manufacturer's instructions. If the timing light has three wires, one, usually green or blue, is attached to the No. 1 spark plug with an adapter. The other wires are connected to the battery. The red wire goes to the positive side of the battery and the black wire is connected to the negative terminal of the battery.
- Leave the vacuum hose connected to the distributor advance vacuum diaphragm on all models through 1979.
On 1980 models: disconnect the throttle valve switch harness connector (810 only). Disconnect and plug the canister purge hose from the intake manifold (810 only). Plug the opening in the intake manifold. On 1980 49 State models, also disconnect the hoe from the air induction pipe and cap the pipe, and disconnect and plug the vacuum advance hose at the distributor. Note that the disconnect and plug instructions for the air induction pipe and the distributor vacuum advance do not apply to 1980 models sold in Canada.
- Check that all of the wires clear the fan, pulleys, and belts, and then start the engine. Allow the engine to reach normal operating temperature.
- Adjust the idle to the correct setting. See the Idle Speed and Mixture section later in this information.
- Aim the timing light at the timing marks. If the marks which you put on the pulley and the engine are aligned when the light flashes, the timing is correct. Turn off the engine and remove the tachometer and the timing light. If the marks are not in alignment, 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 pulley and the marks on the engine, turn the distributor in the direction of rotor rotation to retard the spark, and 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.
- Tighten the distributor lockbolt and recheck the timing.
- Disconnect the wiring harness of the distributor from the engine harness.
- Connect the black wire of the engine harness to the black wire of the distributor harness with a jumper wire. This connects the advanced set of points.
- With the engine idling, adjust the ignition timing by rotating the distributor.
- Disconnect the jumper wire from the black wire of the distributor harness and connect it to the yellow wire of the distributor harness. The retarded set of points is now activated.
- With the engine idling, check the ignition timing. The timing should be retarded from the advanced setting 7°.
- To adjust the out of phase angle of the ignition timing, loosen the adjuster plate set screws on the same side as the retarded set of points.
- Place the blade of a screwdriver in the adjusting notch of the adjuster plate and turn the adjuster plate as required to obtain the correct retarded ignition timing specification. The ignition timing is retarded when the adjuster plate is turned counterclockwise. There are graduations on the adjuster plate to make the adjustment easier. One graduation is equal to 4° of crankcase rotation.
- Replace the distributor cap, start the engine and check the ignition timing with the retarded set of points activated (yellow wire of the distributor wiring harness connected to the black wire of the engine wiring harness).
- Repeat the steps above as necessary to gain the proper retarded ignition timing.