Mechanical Vacuum Pump:
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Assists the actuation of crucial vehicle safety components
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Produces negative pressure
Combined Vacuum-Fuel Pump:
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Combines both the vacuum and fuel pump into one housing
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Useful for space saving in the engine bay
Troubleshooting:
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Symptoms:
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Rattling or tapping noise from vacuum pump
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Insufficient brake power
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Car falling into ‘limp mode’
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Possible causes for failure:
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Cam disc has worn cam roller which drives the vacuum pump
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Pump is worn due to a lack of lubricating oil
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Fuel leak in combined vacuum-fuel pumps
Testing:
The vacuum pump creates a strong vacuum force so ensure the ignition is turned off before testing.
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The first check is to look at the vacuum pump. Disconnect the brake booster fitting from the pump and connect a vacuum gauge.
Turn the ignition on and measure the amount of vacuum being generated. If a measurement of around 20 inHg is being registered this suggests the vacuum pump is generating a good level of pressure. If this is lower than 20 inHg then this suggests that the pump is not generating sufficient pressure and needs replacing.
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If the vacuum is generating sufficient pressure disconnect the hosing from the supply side of the vacuum and hook the gauge to the hosing and check for leaks. If the reading is below10 inHg, this suggests there is a leak.
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If both are functioning correctly then further components in the vacuum system will need to be tested individually using a hand held vacuum pump (such as central locking and braking systems).
Other components to check:
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Individual components which utilise the vacuum generated by the pump such as central locking and brake boosters
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Vacuum pipes – if the vacuum pipes are damaged the correct amount of pressure may not be reaching the components it actuates
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Oil supply – if the oil supply is low this may signal that there is a leak in the system
