DESCRIPTION
Deceleration systems reduce HC emissions through the use various devices. On Colt and Colt Vista models a dashpot and a deceleration spark advance system consisting of an engine speed sensor and solenoid valve is used. On Ram-50 Pickups, air switching valve, coasting air valve and dashpot (all Man. Trans. models except Federal Pickups) are used.
Air switching valve cuts off fuel to by-pass holes and pilot outlet by supplying additional air to slow idle passage. Coasting air valve supplies additional air to intake manifold. Deceleration spark advance system advances ignition timing by changing vacuum supplied to valve from carburetor ported intake vacuum to intake manifold vacuum.
AIR SWITCHING VALVE
When engine speed sensor detects 1500-2500 RPM, it deactivates air switching valve by opening solenoid valve. This maintains smooth vehicle operation during engine mode transient stage and prevents engine stalling.
Air Switching Valve Note flow direction and connections. Scheme 6
COASTING AIR VALVE
When engine speed sensor detects 1500-2500 RPM, it deactivates coasting air valve by opening solenoid valve. This maintains smooth vehicle operation during engine mode transient stage and prevents engine stalling.
Coasting Air Valve Note flow direction and connections. Scheme 7
DASHPOT
On all models with manual transmissions except Federal Pickups, carburetor is equipped with a dashpot. Dashpot delays throttle valve closure to its normal idling position, reducing HC emissions.
DECELERATION SPARK ADVANCE
When engine speed sensor detects 1500-2500 RPM, it activates solenoid valve movement. This changes intake manifold vacuum to carburetor ported vacuum, maintaining smooth vehicle operation.
Deceleration Spark Advance System. Scheme 8
With engine idling, push up dashpot free lever to touch dashpot adjusting screw. Turn screw to set idle speed to 1900-2100 RPM.
AIR SWITCHING VALVE SYSTEM
- Run engine at idle. Disconnect solenoid valve connector to disable solenoid valve. Manifold vacuum will act on air switching valve, causing valve to open. If idle drops excessively or engine stalls, air switching valve and solenoid valve are okay.
- If idle speed does not change, check vacuum passage for clogging and check condition of air switching valve or solenoid valve.
- With engine idling, battery voltage should be measured at solenoid connector. If voltage is not present, electrical wiring or engine speed sensor is defective.
- Increase engine speed to 1500 RPM. Check to make sure voltage is present at solenoid valve connector. If not, engine speed sensor is defective.
- Increase engine speed to 2500 RPM. Check to be sure no voltage is present at solenoid valve connector. If it is, engine speed sensor is defective.