1979 Pickups
- With engine at normal operating temperature, disconnect Neutral switch (Man. Trans.) or inhibitor switch (Auto. Trans.). Place transmission in Neutral.
- Disconnect anti-dieseling solenoid. Connect harness side of connector to a voltmeter and ground the other voltmeter lead. Connect solenoid valve side of connector directly to positive battery terminal.
- Disconnect fuel shut-off vacuum switch-to-intake manifold vacuum hose. Install a vacuum "T" fitting in hose, then reconnect hose to switch. Connect vacuum gauge to "T" fitting.
- Start and run engine. Increase engine speed to 2500-3000 RPM, quickly close throttle, and note vacuum gauge and voltmeter readings. Vacuum should rise quickly to at least 24 in. Hg as throttle is closed. Voltage should quickly drop from 12 to zero (0) volts as throttle is closed.
- Check vacuum switch operating pressure with engine at idle. Operating pressure should be 23-24 in. Hg. If not, remove rubber cap from vacuum switch. See Fig 1. Turn adjusting nut clockwise to increase operating pressure and counterclockwise to decrease pressure.
NOTE:
After each operating pressure adjustment, race engine and recheck pressure to ensure adjustment is correct.