How to check distributor centrifugal and vacuum advance

Written by dan ferrell
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Centrifugal and vacuum advance in a distributor seem like an intricate operational system. In fact, it is an ingenious mechanism to match the spark in the ignition system with the movement of your right foot over the accelerator. However, when problems in the distributor advance system show up, you feel the engine having trouble during acceleration or hear small explosions coming from the engine. Ultimately, engine power decreases and fuel consumption increases. Here, we will test the timing advance mechanism found in contact point-type distributors with some simple steps. You do not need advanced knowledge of car engines.

Skill level:

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Things you need

  • Timing light

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  1. 1

    Open the bonnet of your car and hook up a timing light to the engine. Connect the red alligator clip to the positive terminal of the battery and the black one to the negative side. Now, hook up the timing light’s inductive pickup clamp to spark plug wire #1, the closest one to the front of the engine. Make sure cables and wires are not in the way of moving parts.

  2. 2

    Set the transmission to neutral or park and apply the parking brakes.

  3. 3

    Disconnect the vacuum hose from the distributor.

  4. 4

    Start the engine and let it idle.

  5. 5

    Aim the timing light at the timing mark on the engine while increasing engine RPM to about 3,500.

  6. 6

    Watch the timing mark closely. If the mark advanced smoothly while increasing engine speed, the distributor centrifugal advance is working properly. Otherwise, parts in the system within the distributor might be worn out or rusted.

  7. 7

    Increase the engine speed to about 1,500 RPM and aim the timing light at the timing mark on the engine again and watch its location.

  8. 8

    Reconnect the vacuum hose to the distributor. The timing mark should advance and engine speed should increase. If the advance system did not respond properly to either one of these tests, take the car to an auto shop for inspection.

Tips and warnings

  • If you do not own or have access to a timing light, you may rent one from a major auto parts store.
  • Consult your vehicle service manual to locate and identify components. You can buy one at most auto parts stores or consult one for free at your local public library.
  • When working on a running engine, make sure to keep wires, cables and your arms and hands away from moving parts to prevent damage to equipment and serious injuries to yourself.

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