How to Use a Tach Dwell Meter

A dwell meter is used to check the dwell angle on vehicles with a points-type ignition. Dwell angle is the length of time (measured by the degree of rotation of the distributor cam) the contact points open on a points-type ignition system. Points-type ignition systems were commonly used on vehicles manufactured before the mid-1970s. The dwell angle must be periodically checked on these vehicles to ensure proper operation of the ignition system. In addition, the dwell angle on these vehicles must be checked before setting the ignition timing.

Run the engine long enough to bring it up to normal operating temperature and then shut it off.

Connect the positive lead on the tache dwell meter to the positive terminal on the ignition coil.

Connect the negative lead on the tache dwell meter to the negative terminal on the ignition coil.

Open the small metal cover on the side of the distributor cap and insert an Allen wrench into the screw behind the cover.

Turn the engine on.

Take the reading on the tache dwell meter and compare it with the figure on the engine tune-up decal in the engine bay or in the vehicle's service manual.

Turn the Allen wrench slowly to adjust the dwell angle to the correct setting.

Turn the engine off.

Remove the Allen wrench from the distributor. Make sure the small metal cover on the side of the distributor is closed.

Remove the electrical leads from the ignition coil.

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