Except 1973 610 Models
The spark timing control system has been used in different forms on NissanDatsuns since 1972. The first system, Transmission Controlled Spark System (TCS) was used on most Nissan/Datsuns through 1979. This system consists of a thermal vacuum valve, a vacuum switching valve, a high gear detecting switch, and a number of vacuum hoses. Basically, the system is designed to retard full spark advance except when the car is in high gear and the engine is at normal operating temperature. At all other times, the spark advance is retarded to one degree or another.
The 1980 and later Spark Timing Control System replaces the TCS system. The major difference is that it works solely from engine water temperature changes rather than a transmission mounted switch. The system includes a thermal vacuum valve, a vacuum delay valve, and attendant hoses. It performs the same function as the earlier TCS system. To retard full spark advance at times when high levels of pollutants would otherwise be given off.1973 610 With Dual Point Distributor
The dual point distributor has two sets of breaker points which operate independently of each other and are positioned with a relative phase angle of 7° apart. This makes one set the advanced points and the other set the retarded points.
The two sets of points, which mechanically operate continuously, are connected in parallel to the primary side of the ignition circuit. One set of points controls the firing of the spark plugs and hence, the ignition timing, depending on whether or not the retarded set of points is energized.
When both sets of points are electrically energized, the first set to open (the advanced set, 7° sooner) has no control over breaking the ignition coil primary circuit because the retarded set is still closed and maintaining a complete circuit to ground. When the retarded set of points opens, the advanced set is still open, and the primary circuit is broken causing the electromagnetic field in the coil to collapse and the ignition spark is produced.
When the retarded set of points is removed from the primary ignition circuit through the operation of a distributor relay inserted into the retarded points circuit, the advanced set of points controls the primary circuit. The retarded set of points is activated as follows:
The retarded set of points is activated only while the throttle is partially open, the temperature is above 50°F (10°C) and the transmission is any gear but fourth gear.
When the ambient temperature is below 30°F (-1°C), the retarded set of points is removed from the ignition circuit no matter what switch is ON.
In the case of an automatic transmission, the retarded set of points is activated at all times except under heavy acceleration and high speed cruising (wide open throttle) with the ambient temperature about 50°F (10°C).
There are three switches which control the operation of the distributor relay. All of the switches must be ON in order to energize the distributor relay, thus energizing the retarded set of points.
The switches and their operation are as follows:
A transmission switch located in the transmission closes an electrical circuit when the transmission is all gears except Fourth gear.
A throttle switch located on the throttle linkage at the carburetor is ON when the throttle valve is removed within a 45° angle.
The temperature sensing switch is located near the hood release level inside the passenger compartment. The temperature sensing switch comes on between 41°F (5°C) and 55°F (13°C) and rising and goes OFF above 34°F (1°C) when the temperature falls.
The distributor vacuum advance mechanism produced a spark advance based on the amount of vacuum in the intake manifold. With a high vacuum, less air/fuel mixture enters the engine cylinders and the mixture is therefore less highly compressed. Consequently, this mixture burns more slowly and the advance mechanism gives it more time to burn. This longer burning time results in higher combustion temperatures at peak pressure and hence, more time for nitrogen to react with oxygen and form nitrogen oxides (NOx). At the same time, this advanced timing results in less complete combustion due to the greater area of cylinder wall (quench area) exposed at the instant of ignition. This cooled fuel will not burn as readily and hence, results in higher unburned hydrocarbons (HC). The production of NOx and HC resulting from the vacuum advance is highest during the moderate acceleration in lower gears.
Retardation of the ignition timing is necessary to reduce NOx and HC emissions. Various ways of retarding the ignition spark have been used in automobiles, all of which remove vacuum to the distributor vacuum advance mechanism at different times under certain conditions. Another way of accomplishing the same goal is the dual point distributor system.
INSPECTION & ADJUSTMENTS
Except 1973 610 Models
Normally the TCS and Spark Timing Control systems should be trouble-free. However, if you suspect a problem in the system, first check to make sure all wiring (if so equipped) and hoses are connected and free from dirt. Also check to make sure the distributor vacuum advance is working properly. If everything appears all right, connect a timing light to the engine and make sure the initial timing is correct. On vehicles with the TCS system, run the engine until it reaches normal operating temperature, and then have an assistant sit in the car and shift the transmission through all the gears slowly. If the system is functioning properly, the timing will be 10-15° advanced in high gear (compared to the other gear positions). If the system is still not operating correctly, you will have to check for continuity at all the connections with a test light.
To test the Spark Timing Control System, connect a timing light and check the ignition timing while the temperature gauge is in the cold position. Write down the reading. Allow the engine to run with the timing light attached until the temperature needle reaches the center of the gauge. As the engine is warming up, check with the timing light to make sure the ignition timing retards. When the temperature needle is in the middle of the gauge, the ignition timing should advance from its previous position. If the ignition timing does not change, replace the thermal vacuum valve.TRANSMISSION SWITCH
Disconnect the electrical leads at the switch and connect a self powered test light to the electrical leads. The switch should conduct electricity only when the gearshift is moved to fourth gear.
If the switch fails to perform in the above manner, replace it with a new one.THROTTLE SWITCH
The throttle switch located on the throttle linkage at the carburetor is checked with a self powered test light. Disconnect the electrical leads of the switch and connect the test light. The switch should not conduct current when the throttle valve is closed or opened, up to 45°. When the throttle is fully opened, the switch should conduct current.TEMPERATURE SENSING SWITCH
The temperature sensing switch mounted in the passenger compartment near the hood release lever should not conduct current when the temperature is above 55°F (13°C) when connected to a self powered test light as previously outlined for the throttle switch.