How to Use a Vac Gauge to Set Timing

A properly tuned engine will operate at peak efficiency and in turn use less fuel. The ignition timing is a critical part of engine operation that's directly related to fuel economy. Over time internal parts wear out and cause the precise factory set timing to be lost. Fortunately, there is a way of checking and setting the timing that does not involve complex repairs or expensive professional work. Use a simple vacuum gauge to monitor and adjust the ignition timing.

Things You'll Need

  • Wheel chock
  • Vacuum T
  • Vacuum hose
  • Vacuum gauge
  • Distributor wrench
  • Shift the vehicle to "park" for an automatic transmission or to "neutral" if it is a manual transmission. Place a wheel chock under the rear wheel. Start the engine and bring it to normal operating temperature. Turn the engine off.

  • Locate the intake manifold and find a vacuum port. A vacuum port may or may not have a vacuum hose already attached to it. Locate a manifold vacuum source, normally a port either on the intake manifold itself or at the base of the carburetor or throttle body. Attach the vacuum gauge to the manifold vacuum source. Do not disconnect any vacuum hoses as this may give a false reading; instead, tap into the existing hose using a short piece of vacuum hose or vacuum T, as required.

  • Start the engine and observe the vacuum reading. A normal engine will run from 15 to 24 inches of vacuum at idle. If the vacuum gauge reads "0" then relocate the connection to another vacuum port.

  • Loosen the distributor hold-down bolt using a distributor wrench. Turn the distributor very slowly back and forth until the maximum vacuum reading is shown on the gauge. Back off the timing 2 to 3 inches from the maximum reading. Tighten down the distributor hold-down bolt.

  • Remove the vacuum gauge from the engine and reconnect any hoses that you removed. Remove the wheel chock. Test drive the vehicle and listen for any pinging noises or observe any lack of power. Repeat Steps 1 to 4 if the engine pings or has a serious lack of power.