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| - | '''Transmission Controlled Vacuum Advance System'' (TCVAS) is an emission control system used starting with 1972 USA models. This system provides the vacuum advance only when the gear is in the top (4th) position, and retarded spark timing (with no vacuum advance) at other positions for complete combustion. For satisfactory performance during engine warm-up, TCVAS is disabled until the temperature warms up. | + | '''Transmission Controlled Vacuum Advance System''' (TCVAS) is an emission control system used starting with 1972 USA models. This system provides the vacuum advance only when the gear is in the top (4th) position, and retarded spark timing (with no vacuum advance) at other positions for complete combustion. For satisfactory performance during engine warm-up, TCVAS is disabled until the temperature warms up. |
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| The thermostatic switch: | The thermostatic switch: | ||
| * Conducts between 41F and 55 F as temperature rises | * Conducts between 41F and 55 F as temperature rises | ||
| - | * Conducts above 34F when temperature falls | + | ** Ohmmeter should indicates 0 above 55 degrees |
| + | * Disconnects below 34F as temperature falls | ||
| + | ** Ohmmeter should indicate infinity (~) below 34 degrees | ||
| Tip: To prevent advance cut-out, leave heater off | Tip: To prevent advance cut-out, leave heater off | ||
| Line 39: | Line 41: | ||
| If you neglect to connect the top switch, | If you neglect to connect the top switch, | ||
| - | vacuum advance works normally. | + | vacuum advance works normally. |
| So this is nearly a foolproof system. If any electrical component goes bad or is not connected, normal operation occurs. Only when every electric circuit is working does it cut vacuum advance. | So this is nearly a foolproof system. If any electrical component goes bad or is not connected, normal operation occurs. Only when every electric circuit is working does it cut vacuum advance. | ||
| + | |||
| + | = Vacuum Hoses = | ||
| + | Vacuum advance in all models uses a hose from the Distributor to the 'port' on the carburetor. TCVAS adds to this, by adding a 'T" line. The 'T' carries vacuum to the '''Vacuum Cutting Valve Solenoid''', which when electrically powered, dumps the vacuum through a small orifice connected to air. This effectively 'cuts' vacuum advance, while the small orifice prevents a vacuum leak. | ||
| + | |||
| + | The source of air to the Valve is both: | ||
| + | * underside of air cleaner | ||
| + | * Flow guide valve | ||
| [[Category:Emission Control And Tune-Up]] | [[Category:Emission Control And Tune-Up]] | ||
Revision as of 17:26, 28 December 2007
Transmission Controlled Vacuum Advance System (TCVAS) is an emission control system used starting with 1972 USA models. This system provides the vacuum advance only when the gear is in the top (4th) position, and retarded spark timing (with no vacuum advance) at other positions for complete combustion. For satisfactory performance during engine warm-up, TCVAS is disabled until the temperature warms up.
Thermo Switch
The thermo switch is located inside the passenger compartment:
Location: Under dash, right side of car
The thermostatic switch:
- Conducts between 41F and 55 F as temperature rises
- Ohmmeter should indicates 0 above 55 degrees
- Disconnects below 34F as temperature falls
- Ohmmeter should indicate infinity (~) below 34 degrees
Tip: To prevent advance cut-out, leave heater off and roll down the windows.
Schematic
Both vacuum and electricity are used.
In cold weather, vacuum advance is normal Until car warms up...
56-series 4-speed (LHD)
- Reverse lights switch
- Top switch (emission controlled models)
When current flows to the Vacuum Cutting Solenoid, it cuts the vacuum advance.
If the Solenoid is disconnected, vacuum advance works normally.
The Top Switch is normally open (allowing current). Only in top gear (4th) does it become electrically closed.
If you neglect to connect the top switch, vacuum advance works normally.
So this is nearly a foolproof system. If any electrical component goes bad or is not connected, normal operation occurs. Only when every electric circuit is working does it cut vacuum advance.
Vacuum Hoses
Vacuum advance in all models uses a hose from the Distributor to the 'port' on the carburetor. TCVAS adds to this, by adding a 'T" line. The 'T' carries vacuum to the Vacuum Cutting Valve Solenoid, which when electrically powered, dumps the vacuum through a small orifice connected to air. This effectively 'cuts' vacuum advance, while the small orifice prevents a vacuum leak.
The source of air to the Valve is both:
- underside of air cleaner
- Flow guide valve