How to Find an Engine Vacuum Leak

Written by david montoya
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How to Find an Engine Vacuum Leak
Engine vacuum leaks often cause engine idling. (new car engine with red trim image by Raxxillion from

Engine vacuum leaks are notoriously difficult to find, but their symptoms are all too apparent. The most common problems associated with a vacuum leak are lean fuel burning and engine idling. This happens because the leaks are allowing too much oxygen to enter the engine. This, in turn, upsets the delicate oxygen-to-fuel ratio necessary for efficient internal combustion. Too much oxygen means inadequate fuel is running through the engine. This also causes your engine to work harder, an issue that can create other problems down the road. Nip the problem in the bud by using an automobile smoke machine.

Skill level:

Things you need

  • Automobile smoke machine

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  1. 1

    Turn off your car and lift the bonnet to your engine. You need the engine to be off before you start this project to ensure the bonnet isn't hot to the touch when you lift it. The moving parts within the engine pose their own dangers as well. A loose article of clothing or a careless placement of your hand can cause serious injury or damage your car. This is an easy step and maybe even an obvious one, but an important one nonetheless.

  2. 2

    Inspect the vacuum hoses leading to the engine check for cracks, holes or loose connections. Most of the time engine vacuum leaks will be difficult to spot. Taking this step will help identify the problem on the rare occasions that your vacuum hose damage is readily apparent.

  3. 3

    Open the evaporator system service port. This is the port covered with a small green cap. Now attach the automobile smoke machine to the port using the hose fittings on the smoke machine.

  4. 4

    Turn your car engine on and start the smoke machine. Smoke will start to flow through the vacuum tubes in your car. Any cracks or pinholes will start spewing out smoke. Make note of the locations of the leaks. Cracks and pinholes will require new hoses to be placed in your car. Loose-fitting hoses may only require an adjustment. If none of the vacuum hoses show signs of smoking, your car problems are most likely not being causes by an engine vacuum leak.

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