A dwell meter measures the amount of time that the points remain closed or "dwell together" when an engine is running. These specifications only apply to vehicles that were made using the old points/plug/condenser ignition. Modern vehicles that use electronic ignition no longer have points, so these steps are not applicable. Dwell figures for any specific engine are found in service manuals that outline engine tuning, and these figures must be referenced for proper use of a dwell meter. For vehicles that rely on older style ignitions, dwell meter readings are a must for doing a proper tuneup.
Attach a dwell meter to your ignition system. The black lead gets clipped onto a ground or solid metal part of the vehicle body, and the red lead gets clipped onto the distributor side of the coil where the wire meets the distributor.
Run the engine if the distributor has an adjustment window, or remove the distributor cap and crank the engine once the ignition wire has been grounded. With the engine running or cranking, read the figures on the dwell meter.
Compare dwell meter readings with official engine specifications. These can be found in any service or repair manual specific to your engine. However, basic readings for an 8-cylinder engine will be about 30 degrees of dwell. For a 6-cylinder engine, the dwell meter will show about 35 degrees of dwell, and for a 4-cylinder engine, you will see about 45 degrees of dwell. These are not exact figures as all engines have very specific dwell angle requirements.
Look for dwell meter readings to remain constant when the engine is being run or during engine cranking. Bouncing or erratic dwell meter readings means there is a problem with either the distributor, the distributor cam or the points. A variation of 3 degrees of dwell signals that the distributor needs replacement or rebuilding.
