How to Use a Vacuum Gage to Check a Car Engine
There are many functions on an automobile that can be monitored by the engine's gauge panel. Oil pressure, fuel levels and even the charging system are represented on the dashboard of most vehicles. Wouldn't it be nice if there was a gauge specifically designed to perform engine diagnostics? Imagine being able to look at your dashboard and identify such engine problems as a clogged exhaust or even a blown head gasket. These are problems that most vehicle owners are forced to have diagnosed by a professional mechanic. But there is a gauge that will help you identify these problems: a vacuum gauge.
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Instructions
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1
Park vehicle on a flat hard surface. Place the vehicle in "park" or "neutral" if it is a stick shift. Set the parking brake and open the hood.
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Locate a vacuum hose in the engine compartment. This must be a simple manifold source and not a ported manifold source. In most cases, this will be a direct manifold source. Note that in EFI (electronic fuel injection) equipped vehicles, this is best accomplished by teeing into the source line from the heater system.
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3
Insert the gauge into the hose. Using the T-fitting from the vacuum gauge kit, insert the T into the vacuum line by pulling the line from its nipple on the manifold and placing it on one nipple of the T. Place the other T nipple into the vacuum port where you removed the line. The last nipple of the T is connected to the hose leading to the gauge.
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4
Start the engine. With the engine running, monitor the vacuum gauge, making notes on the needle's behavior. Compare this behavior to the chart that accompanies the gauge. The gauge will identify problems such as clogged exhaust, worn valves and guides, leaky manifolds and poor head gaskets. Even bad timing or incorrect fuel mixture can be detected with a vacuum gauge.
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Make the required repairs. Correct the detected problems and run the engine again to watch the gauge. When all is well, disconnect vacuum gauge, reinstall the vehicle's vacuum hose in the manifold's nipple and close hood.
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Tips & Warnings
It is often easiest to have a helper sit inside the vehicle and rev the engine, if needed.
