What is a dwell meter?

unless it's the automotive variety, probably not. but don't worry about it. if your car has electronic ignition, it's irrelevant because "dwell" is all determined by the ecu or ignition module. all that matters is that the igniter switches, that the coil fires, and that the plugs spark.

use of the word "dwell" is a throwback to the old days of contact breakers where the contacts had to "dwell" for long enough to energize the coil. too little dwell, not enough spark energy, especially at high rpm's. too much, coil ran too hot.

In the old mechanical breaker points ignition systems, dwell angle is the angle of rotation of the distributor through which the mechanical points are "closed. The points must remain closed for a sufficient time to store energy in the coil sufficient to produce a good, hot spark at the plug when the points open. In a four cylinder engine, dwell angle is typically around 60 degrees.

There is an equivalent measurement in an electronoic ignition system that is usually called dwell, but it is not properly dwell in the old contact points sense. This quantity is electronically controlled. I am not sure what an old fashioned dwell meter would be measuring in a modern electronic ignition engine. However, I do not think it would be useful information. There is typically no way to make adjustments on most electronic ignition systems anyway.

Hope this helps.

Elliot Richmond Freelance Science Writer and Editor

The 'Old' Dwell meters were usually based on continuity testers. I suppose you could measure continuity with it. I have seen articles in the electronic trade magazines about using Volt-Ohm (V.O.M.)meters for measuring point dwell. This was back in the late sixties and early seventies. I know I'm showing my age here.

Randy

Young whippersnapper!

My dwell meter scale read in degrees. I never took it apart but my guess was that it was some sort of RC circuit (or maybe IRC) with a voltmeter reading the potential across the capacitor. The longer the dwell, the more charge the capacitor would accumulate, and the higher the voltage, which would then read as a larger dwell angle.

Elliot Richmond Freelance Science Writer and Editor

That's how I would build one - dead simple :)

Some of them would simply let the longer the dwell be indicated by the lower resistance read. Letting the mechanical inertia of the meter integrating the pulses into a smooth reading.

Randy

There should be no change in resistance - either it's infinite (points open) or near-zero (points closed).

That's how almost all tachometers work.

Replace the dwell with a spare bulb from the taillights.

Yes/No. If the coil is severely dead there is no load. And no load = no signal. That's why the bulb works.

"Elliot Richmond" wrote

A dwell meter can measure fuel injector's richness, although the correct way is to measure current.

dwell is the number of degrees the points were open, for an ignitior it's faster to use a common test light. Chip