Vacuum System Diagnosis
- Block wheels. Apply parking brake. Place automatic transmission in Park or manual transmission in Neutral. Connect vacuum gauge to vacuum pump inlet. See Fig 1
. If applicable, disconnect outlet hose from outlet tube on pump and plug end of hose. DO NOT plug vacuum pump outlet tube.
- Start and run engine at idle. Minimum vacuum reading should be 21 in. Hg at sea level, within 30 seconds. For higher altitudes, compensate vacuum reading according to graph. See Fig 1
. If vacuum reading is correct, go to step 4).
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- If vacuum reading is low or fluctuating, check gauge and connections for leaks. If pump is belt driven, check belt tension and pulley fit to shaft. Check and adjust idle speed as necessary. Recheck vacuum reading. If reading is still low, replace vacuum pump. If reading is now okay, go to next step.
- If applicable, remove plug from outlet hose and reconnect hose to pump. Reconnect inlet hose to pump with a "T" fitting and vacuum gauge. See Fig 2
. With engine idling, vacuum may be 3 in. Hg less than that measured in step 1) after one minute.
- If vacuum reading is correct, remaining problems are not in vacuum system. If vacuum reading is lower than specified, check hoses for leaks and repair as necessary. If vacuum reading is still low, check vacuum operated components for leaks. Repair or replace as necessary.
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