DESCRIPTION
The Spark Timing Control system is designed to control distributor vacuum advance under varying driving conditions to reduce HC and NOx emissions. This is accomplished by the use of a thermal vacuum valve (TVV). A vacuum control valve is also used on Pickup.
SYSTEM CHECK
On all models, ensure all vacuum hoses are in good condition and properly connected. Place transmission in Neutral or Park. With engine cold, connect timing light. Start engine and note timing. If timing is not to specification, loosen distributor clamp bolt and turn distributor until specified ignition timing is obtained. Retighten distributor clamp bolt.
Spark Timing Control System (Pickup, Stanza & 200SX). Scheme 7
Thermal Vacuum Valve (TVV)
The thermal vacuum valve is mounted on the front of the intake manifold. It detects engine coolant temperature by means of wax, and opens or closes the vacuum passage in the thermal vacuum valve. When the valve opens, the vacuum signal line will allow external air to enter, thereby stopping the distributor vacuum from advancing.
Vacuum Control Valve
The vacuum control valve in installed in the distributor vacuum line. When the carburetor venturi vacuum exceeds the pre-set value, the air is bled to the distributor vacuum line and then, the spark timing retards slightly.
Thermal Vacuum Valve
Note. The thermal vacuum valve is a major component of the EGR system. Test procedures for various thermal vacuum valves are contained in EXHAUST GAS RECIRCULATION SYSTEM article.
Drain cooling system. Remove thermal vacuum valve from engine. Immerse valve in water. DO NOT allow water to get inside. Apply suction from port of spark timing control system and check that thermal vacuum valve opens or closes in response to its temperature. Valve should be closed when water temperature is below 59° F (15° C); open between 59-122° F (15-50° C), and closed above 122° F (50° C). DO NOT allow water to get inside the thermal vacuum valve.
Apply vacuum to vacuum control valve, and ensure that distributor side of vacuum control valve opens or closes in response to the vacuum of carburetor side. Valve should be open when more than 1.97 in. Hg of vacuum is applied, and closed when less than 1.97 in. Hg of vacuum is applied.
Ensure all vacuum hoses are in good condition and properly connected. Place transmission in Neutral or Park. With engine cold, connect timing light. Start engine and note timing. If timing is not to specification, loosen distributor clamp bolt and turn distributor until specified ignition timing is obtained. Retighten distributor clamp bolt.
| Application | Man. Trans. | (1) Auto. Trans. | ||
|---|---|---|---|---|
| 1986 Pickup | ||||
| M.P.G. Models | 5 @ 600-800 | N/A | ||
| All Others | ||||
| 2WD | 3 @ 600-800 | 3 @ 550-750 | ||
| 4WD | 3 @ 700-900 | 3 @ 550-750 | ||
| Pulsar NX | ||||
| Federal | 10 @ 700-900 | 10 @ 550-750 | ||
| Calif. | (2) 5 @ 700-800 | (2) 5 @ 600-700 | ||
| Sentra | ||||
| Federal | 10 @ 700-900 | 10 @ 550-750 | ||
| Calif. | (2) 5 @ 700-800 | (2) 5 @ 600-700 | ||
| Stanza | 0 @ 650-850 | 0 @ 600-800 | ||
| Stanza Wagon | 4 @ 650-850 | 4 @ 600-800 | ||
| 200SX | 0 @ 650-850 | 0 @ 600-800 | ||
| (1) With Auto. Trans. selector in "D" position. (2) Degrees are ATDC. | ||||
| (1) | With Auto. Trans. selector in "D" position. |
| (2) | Degrees are ATDC. |
IGNITION TIMING (Degrees BTDC @ RPM)
