How to Connect a Vacuum Gauge

Written by richard rowe
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How to Connect a Vacuum Gauge
Vacuum indicates airflow, which plays an important role in fuel economy. (engine image by goce risteski from

Vacuum itself doesn't have anything to do with fuel economy, but it does give a strong indication of how much fuel the engine is using. Vacuum, or boost gauges measure the negative pounds per square inch (psi) of pressure in the intake system, allowing you to adjust your driving style to extract the maximum possible fuel economy from your automobile. Gauge installation varies by vehicle, gauge type and preferred mounting location, but the gauge-connection procedure will vary little.

Skill level:

Things you need

  • Gauge installation kit
  • Drill and drill bits
  • Razor blade
  • Zip ties

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  1. 1

    Drill a 3/8-inch or 1/2-inch hole in your firewall to pass the gauge sensor line through from the car interior to the engine bay. The size hole you'll need depends on the specific gauge you use and the type of sensor line. If your gauge uses 1/4-inch rubber vacuum line, drill a 1/2-inch hole and install a rubber grommet into the hole with a 3/8-inch hole in the centre. Just above the brake pedal is usually a safe spot to drill.

  2. 2

    Slide the rubber vacuum line over the barbed fitting on the back of your vacuum gauge, then feed the line through the hole in your firewall. Route the line upward through your engine bay and toward the intake manifold. Use zip-ties to secure the line to your firewall, making very sure not to kink it or allow it anywhere near hot or moving engine components. Lay the line on top of your intake manifold, but leave about 6 inches of slack to allow for engine movement.

  3. 3

    Locate a 1/4-inch vacuum line on your intake manifold. Neophyte installers might be tempted to use one of the several vacuum lines coming off the throttle body or carburettor, but don't do it. These "ported" vacuum sources read vacuum ahead of the throttle plate instead of behind it, and won't give you the fuel economy reading you're looking for.

  4. 4

    Cut the chosen manifold vacuum line with a razor. Where you cut it isn't important, as long as the gauge sensor line will reach the cut area. Plug the supplied T-fitting into one side of the cut line, and plug the other side of the line into the other side of the fitting. Plug the sensor line into the third outlet on your T-fitting.

  5. 5

    Start the engine and have an assistant give the throttle a few quick stabs while you check for kinking or binding in the sensor line. If the engine starts running roughly, check your fittings for a vacuum leak.

Tips and warnings

  • The closer you place your T-fitting to the engine, the quicker the gauge will respond to vacuum changes. Avoid placing the T-fitting in a very large line, as smaller lines yield a more accurate vacuum reading.

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