VENTURI Vacuum Amplifier
NOTE:
Amplifiers have built-in calibrations, and no external adjustments are required. If an amplifier bias test reveals malfunction, replace amplifier. Venturi vacuum amplifier is checked after checking all other basic EGR components.
- Remove hose connecting EGR valve to amplifier at EGR valve end and connect vacuum gauge to hose. By-pass EGR delay valve, if so equipped. Disconnect vacuum hose at reservoir and "T" this line to a manifold vacuum source.
- Start engine and accelerate to 1500 to 2000 RPM, then release throttle to idle speed. Disconnect hose at carburetor venturi. Vacuum should be within ±.3 in. Hg of specified bias value. If specification is zero, vacuum may read up to 0.5 in. Hg. Replace amplifier if not to specification.NOTE: Before performing the following steps, by-pass vacuum solenoid valve or vacuum operated switch, if so equipped.
- Accelerate engine to 1500 to 2000 RPM then release throttle to idle speed. If vacuum gauge increased more than 1 in. Hg during acceleration, replace amplifier. Reconnect venturi hose to carburetor. If output vacuum increases more than 0.5 in. Hg, check idle speed. If idle speed is too high, output vacuum could increase due to increase in venturi vacuum.
- Accelerate engine to 1500 to 2000 RPM and check vacuum gauge. Vacuum should measure above 4 in. Hg during acceleration and return to specified bias when throttle is released. If vacuum does not return to specified bias, replace amplifier.
- Connect "R" nipple to manifold vacuum source, "S" nipple to spark port vacuum, "V" nipple to venturi vacuum, and "O" nipple to vacuum gauge. Accelerate engine to 1500 to 2000 RPM and release throttle to idle speed. Remove vacuum hose at carburetor venturi, and check spark port vacuum. If vacuum is greater than 2 in. Hg, amplifier output vacuum could increase. Vacuum gauge reading should be less than 0.5 in. Hg for all amplifiers. If not to specification, replace amplifier.