What is a dwell meter?

Tegger's FAQs has references to dwell meters - e.g for testing the coil. I
have never heard of a dwell meter before and they aren't widely available
from what I can tell..

Wondering if my digital electric multimeter can do this diagnostic...?
Starting Problems
.... is this: Connect a dwell meter to the negative coil terminal and to
ground.
Crank the engine: No dwell, bad igniter; Dwell but no spark, bad coil. ...
www.tegger.com/hondafaq/startproblems.html

 

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.

 

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