Carburetor: Testing and Inspection

- Chart C-2D Rear Vacuum Brake (RVB) Check.:

- Wiring Diagram for Chart C-2D Rear Vacuum Brake (RVB) Check.:

CHART C-2D, REAR VACUUM BRAKE (RVB) CHECK (VIN 9)

CIRCUIT DESCRIPTION
The rear vacuum brake is mounted on the carburetor and is controlled by a rear vacuum brake solenoid. When the solenoid is energized, no vacuum is applied to the RVB allowing the plunger to extend (rich). When the solenoid is de-energized, manifold vacuum will be applied to the RVB and pull the plunger in (lean). The RVB solenoid is controlled by the ECM. Battery voltage is supplied by ignition and the ground is completed by the ECM to energize the solenoid.
a. RVB solenoid is energized for about 30 seconds during certain cold engine conditions to keep the RVB from applying to improve cold driveability.
b. Poor cold driveability would result if the RVB is applied during initial start-up.

CHART DESCRIPTION
1. Removing the coolant sensor connector simulates a cold engine and would normally allow the RVB plunger to extend for about 30 seconds.
2. This step separates an electrical short to ground from a vacuum problem. By de-energizing the solenoid, the RVB should normally retract.
3. Checks to see if retracted RVB in step one was due to no electrical signal to energize the RVB solenoid, or to a faulty solenoid. The solenoid should be energized with the ignition "ON" and engine stopped. The test light should be "ON" in this step if the electrical circuit is OK.