Fuel Delivery and Air Induction: Description and Operation

This system prevents overheating of the catalytic converter and backfiring in the exhaust during deceleration by momentarily stopping fuel flow through the carburetor under high vacuum conditions. System components include carburetor mounted, micro-processor (computer) controlled fuel cut solenoids, the computer which monitors manifold vacuum and on most models engine RPM, and a vacuum sensor switch. When the fuel cut solenoid circuit is completed to ground, the solenoid valve is retracted and fuel flows through the carburetor slow circuit. When the computer opens the solenoid ground circuit, the valve closes and fuel flow is stopped.

Fig. 25 Deceleration fuel cut system.:

3A-C, 4A-C & 4A-LC ENGINES

In this system, Fig. 25, the fuel cut solenoid ground circuit is completed as long as engine speed is less than 1900 RPM. When engine speed exceeds 2290 RPM, the solenoid ground circuit is completed through the computer as long as manifold vacuum is less than 7.09 inch Hg. When manifold vacuum exceeds 8.46 inches Hg, the vacuum switch is off and the solenoid ground circuit is opened by the computer.