Topic: testing coils with multimeter

[narcoticrex]

so I just hooked up my multimeter to the 2 "gouzinta" wires, and there was no resistance whatsoever - but i forgot to take the plug boots off, which are supposed to have 15 ohms as well?  I should have been reading at least 15 ohms right?  does this need to be done with a 12v battery hooked up?  I only tested it with the power through the multimeter (AA batts, 1.5v).  I thought voltage didnt matter when testing resistance (but its been a long time since i took that class...

[750goes]

you need to measure between the two small wires first (power going in ) - I think this is the small resistance side..
then measure without the plug caps across the spark plug lead ends.... I think this is the large resistance.

also measure the resistance when you join both multimeter leads - this will give you the resistance of your meter and leads which needs to be subtracted from your measured results...

when you have results - post back and someone can tell you whether they are good or not..

[TwoTired]

The spark plug boots have either 5K or 10K ohm resistors in each one, usually.  Measure gozoutas without the boots.  Then measure each boot separately.

An ohmmeter supplies it own voltage to make a measurement.  Don't add any external to the meter, as it determines resistance based on the voltage it gets back from the circuit under test.

Cheers,

[narcoticrex]

hrm , thats what i thought...so i guess that means the coils are shot, as there is no resistance whatsoever...

[TwoTired]

hrm , thats what i thought...so i guess that means the coils are shot, as there is no resistance whatsoever...

No resistance is 0 ohms.  A very low value.  So, a low resistance mean you have continuity and good secondary wires. The coil secondary the "goesouta" has a lot of copper windings and should show some resistance.
Some meters are not auto-ranging.  If you don't select a scale appropriate to the measurement being taken, you don't get a meaningful reading.  This comes under the heading of the tool being smarter than the operator.
Understanding the tool you are using is at least as important as the understanding the device you are trying to measure.

Having said that, a break in the wiring will cause infinite resistance to show on the meter.  If this is what you meant by no resistance, then yes, your coil has a problem.

Cheers,

[narcoticrex]

This comes under the heading of the tool being smarter than the operator.

hey, what you trying to say? 

i got it set for a range of 10 ohms.  when the test probes are apart, infinite resistance.  when i touch the test probes together, sweeps across for zero resistance, as it should. when i measure the two gouzinta wires, zero resistance.   

maybe im just not understanding coils, i thought they were transformers and that transformers have resistance, thats why they measure 5 ohms thru the gouzintas...i understand there should be continuity between the 2 gouzintas, but unimpeded contiuity?  that is the question.  Thank for your responses 2t you teach me something every day 

[TwoTired]

The 1&4 or 2&3 ignition leads should have some resistance between them.  I just measured 14K ohms on a set laying around in the shed.  It's a digital auto ranging meter.

If your's measure a direct short, something's amiss.  Any hatchet marks on the coils?  Bullet holes?  Melty bits?

Are these stock coils?

Cheers,

[750goes]

interesting discussion so far............come on tt..........where is the wit ??

[jjwaller]

The problem is, that unless you have a $300.00 plus
digital multimeter, you can't accurately measure Ohms
with any accuracy. In fact to measure resistance the best thing
is an old analog meter(Simpson 260).  Even fairly cheap Radio Shack analog
meters are generally more accurate than cheap digitals in measuring resistance.
 Now having said that, a coil is nothing more than 2 pieces of wire
wrapped in a circle.  The primary side in high voltage coils is wrapped
with less "turns" than the secondary side in the ratio of step-up in voltage
required. Bottom line is, It may be that you can't measure the inherent
resistance of the length of wire in the primary side of the coil with
your meter.  By the way, the primary and secondary sides of the coils are not
electrically connected.  The voltage is transmitted by inductance i.e. transformer
action.

[MrZxp]

i got it set for a range of 10 ohms.

Isn't this scale a little low? If the resistance is above this threshold the (digital) meter will read 0. (infinite resistance)

Especially since TT just got a reading of 14000 ohms on his spare coils? 10 ohm scale is too low. Switch to 20K, 100K or 200K scale.

Cheers, Phil

[MrZxp]

In fact to measure resistance the best thing is an old analog meter(Simpson 260).

Yes. It is so easy to see a short circuit when you get a FSD (full scale deflection) and that needle swings all the way to the right... (kinda like a rev counter  ) with a digital all you get is a boring instant 0.00 (or 00.0 depending on your scale)! 

Cheers, Phil