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I am unskilled; Help with OHM coil readings

Old 07-08-2009, 01:14 AM
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I am unskilled; Help with OHM coil readings

Hello,

Upon looking at my four coils, they all had those white burnt marks on them. And I've read through this TSB http://www.finishlineperformance.com...16-07-1793.pdf.

I used a cheap multimeter to check up on the actual values of my coils because I wanted a real answer. Well I got numbers I think, but cannot interpret them at the moment (I'm just learning about electrics now).

Here are my preliminary results, though I plan to study more about these values, I'd love your guy's insight.

Multimeter was set at 200. I believe this means 200OHM.

A(+) to B(-) = 1 63, 1 22, 1 46, 1 93

B((+) to C(-) = 1 46, 1 66, 1 39, 1 80

If my way of presenting this information is inadequate or plain stupid, I'm sorry. But this was my first time playing with a multimeter. Any wrongs I've done I welcome correction and input.

I tested two of my coils, what do you guys think?
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Old 07-08-2009, 06:07 AM
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Those are some funky numbers and is probably because you had your meter set to 200ohms.
You probably saw numbers as it was attempting to measure resistance and then displayed "OL" which is an over limit indicator because the value exceeded the range (which was up to 200ohms).
That's when you turn the dial to the next measurement value which should be 2K ohms.
With this you should have a reading across A and B.

I found an old meter similar to what you have and I'll walk you through the steps.
I will also use a better meter because it was needed for my coil (which I'll explain later).

First measuring across terminals A+ and B-
With the RS (Radio Shack) meter set to 2K ohms, I get 1.5k ohms
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The Fluke meter has an auto range feature so I don't have to use a specific range.
But you can see it too reads 1.5k ohms (you can see the "k" on the lower right corner).
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Now when I measured terminals B+ and C- I got the OL indicator, even with my range up to 2M ohms.
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Using my fluke I can see why my little RS meter couldn't read it.
I measured 2.6M ohms across those two terminals with my Fluke meter and my RS meter could only go up to 2M ohms.
A few weeks ago I checked someone's coils and I measured 1.6M ohms across those two terminals.
In that case, I could use my RS meter with the dial set to the 2M ohm range.
So you may be able to read it with your meter, but you'll know why if you can't.
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Now we check for continuity across terminals C+ and A-.
In this case we do NOT want to see any readings and it should read OL


My Fluke meter verifies the same result.
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Hope this helps.

Last edited by Jon316G; 07-10-2009 at 06:35 AM.
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Old 07-08-2009, 07:02 AM
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Nicely presented Jon, as always. For the OP I would only add a bit of general theory.

The "coils" are so named because way back when they were literally loose coils of wire, forming a crude transformer. This transformer is needed to raise the battery's 12 volts to a much higher value to in turn facilitate the mini lightning bolt (spark from sparkplug) that ignites the fuel vapor during the combustion cycle.

However, per Ohm's Law, as voltage increases, amperage increases, with resistance (measured in Ohm's) remaining constant.

E (Electromotive potential, or voltage) = I (amperage or current) x R (resistance) -or- R = E/I

We check the resistance of the coils primarily for continuity, that is, whether there is a normal or abnormal path for the electricity. As the coils burn out (displaying the white spots) the resistance increases and therefore, again according to Ohm's Law, the voltage capable of being transformed diminishes and the coils must be replaced.

Edit - to bring this full circle, the wasted energy from the increased resistance of failing coils is dissipated as increased heat which forms the burn spots on the back of the coils.

Last edited by Huey52; 07-08-2009 at 07:21 AM.
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Old 07-08-2009, 07:05 AM
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Couldn't have said it better Huey52
Thanks for adding the explanation.
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Old 07-08-2009, 10:07 AM
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Remember the resistence can be ok now... butt when the coil heats up the resistance breaks down and it fails.

Coils usually fail in this way.
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Old 07-08-2009, 11:33 AM
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Jon to the rescue!
nice post
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Old 07-08-2009, 12:32 PM
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maybe this should be up on the DIY section for ppl to be able to test their coils!
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Old 07-08-2009, 12:53 PM
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I'm sure by "resistance breaking down" you mean that when heated the coil resistance actually goes up (increases), with the ultimate failure being an open circuit of infinite resistance. Heat is indeed the enemy of electronics, as it is FI and general automotive operation.

Our engines and their support systems are basically heat pumps which are in turn adversely affected by abnormal heat. We can't win!

But we can change our coils, 'plugs, and wires on a regular maintenance schedule.

Originally Posted by Razz1 View Post
Remember the resistence can be ok now... butt when the coil heats up the resistance breaks down and it fails.

Coils usually fail in this way.

Last edited by Huey52; 07-08-2009 at 12:55 PM.
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Old 07-08-2009, 11:58 PM
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Wow.

All of you guys are awesome, I can't thank you right over the internet for the appreciation I have for this info.

The tester I was using was a 4.99 analog my friend got on clearance at a parts store. Today I went out to get myself an Innova 3310 ranging ( I thought auto-ranging would take out the fun of learning about this crap).

Gonna bust the coils outta my car within the week and will post what I get.

That sticky comment isn't a bad idea. Maybe I can take pics, but you guys will have to make up for the information!
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Old 07-09-2009, 12:09 AM
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I just Googled the Innova 3310 meter... not a bad unit.
I would recommend reading the manual that comes with it.
They usually give you information on how to properly perform various measurements, what each setting means, and helpful tips/cautions like not measuring resistance on a circuit that's still powered.
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Old 07-09-2009, 12:44 AM
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as coils tend to fail at hi rpm sometimes only.

what you need to do is get an inductive timing light.. hook it to a spark plug wire. route it under the hood and a wiper..

aim it at the drivers seat about eye level..

go for a drive.. rev the car to where it has an issue.. does the light flash at an increasing pace??? or does it stop..

if it stops you found you problem. if not move to the next coil..

repeat 4 times and you have your answer..

beers
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Old 07-09-2009, 06:40 AM
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And who said that since the advent of electronic ignition there was no longer any use for a timing light.

The Mazda TSB also describes this way of checking coil vitality, but they don't mention at rev, which is a good idea (and of course you need not be driving, just rev in the driveway).
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Old 07-09-2009, 07:57 AM
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Thats why I said "screw" the Mazda's coil test.

The easiest to tell if your coils are shot is, go drive it, push it hard. if you get misfire, 99.99% chance ur coils are shot (assumes u have working battery, alternator, working ECU, working engine harness, good wires and new/good plugs ...)
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Old 07-09-2009, 04:51 PM
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Hmm....now where to find a timing light....
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Old 07-09-2009, 05:40 PM
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The heck with the timing light. You cited you had burn marks Targatheory. Swap out your coils and sleep worry free.

Tommy at Rosenthal Mazda will send you out a set in no time at all.

http://www.finishlineperformance.com...cat=338&page=2
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Old 07-10-2009, 12:39 AM
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A long time ago I wanted the BHR kit. I was just about ready to get them until my financial priorities moved away from my car. Now, unemployment coupled with school and a new single studio is a hinderance...

Anyway, yes, four coils have white smudges on them; is there a reason the Mazda TSB says not to judge coil performance based on these burn marks?

I tested the same two coils as in the opening post with my new (and newly loved) Innova.

The "200" OHM setting gave me nothing on either coils so...

Coil 1 @ 2K
A(+) to B(-) = 1.634
B(+) to C(-) = No Reading
C(+) to A(-) = No Reading (Good, right?)

Coil 2 @ 2K
A(+) to B(-) = 1.692
B(+) to C(-) = No Reading
C(+) to A(-) = No Reading (Again, good, right?)

Up it to 200K...

Coil 1 @ 200K
A(+) to B(-) = 1.6
B(+) to(C(-) = 56.8
C(+) to A(-) = No Reading

Coil 2 @ 200K
A(+) to B(-) = 1.7
B(+) to C(-) = 57.7
C(+) to A(-) = You guessed it, No Reading

So um, being a noob, do my @200K B(+) to C(-) readings mean I am 57,700 OHMS resiliant to normal electrical flow? Yea, that's right, I'm looking into some math touch up classes pretty soon.
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Old 07-10-2009, 06:29 AM
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I speculate that the reason Mazda states in the TSB not to judge the coils solely by the burn marks is that the coils, as inductive loads, may still be viable despite the add'l resistance and therefore dissipated heat that caused the marks. They don't want techs swapping out coils simply on visual observation and therefore go on to cite metering/timing light procedures.

Now, we as uber preventive maintenance types swap ours at this first sign of deterioration - what's the point in waiting for the inevitable failure once they've hit this wear point?

But I do sympathize with your need now to be more frugal and therefore prolong their use.

Yes, your B(+) to C(-) reading indicates that you have 57.7K ohms of resistance to electrical flow. But keep in mind that there will always be some resistance, that is until sometime in the future when we achieve absolute zero-like perfect flow at ambient temps.
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Old 10-04-2014, 04:17 PM
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Hi gentlemen,

I'm having a problem with this. I am getting some strange values from the 4 pulled from the car and one of my brand new ignition coils. I am also using a multimeter, and I think I'm using as described in the test cases above.
Not Used
Black Wire Tester
Red Wire Tester


#1 Ignition Coil Test Results

----20M ------------ 20M ------------- 2K
C:.:B:.:A ------ C:.:B:.:A ------ C:.:B:.:A
---9.58 ----------- 9.59 ------------ 0.961



#2 Ignition Coil Test Results

----20M ------------ 20M ------------- 2K
C:.:B:.:A ------ C:.:B:.:A ------ C:.:B:.:A
---9.50 ----------- 9.50 ------------ 0.9



#3 Ignition Coil Test Results

----20M ------------ 20M ------------- 2K
C:.:B:.:A ------ C:.:B:.:A ------ C:.:B:.:A
---9.46 ----------- 9.46 ------------ 0.90



#4 Ignition Coil Test Results

----20M ------------ 20M ------------- 2K
C:.:B:.:A ------ C:.:B:.:A ------ C:.:B:.:A
---9.68 ----------- 9.7 ------------ 0.912





#NEW Ignition Coil Test Results

----20M ------------ 20M ------------- 2K
C:.:B:.:A ------ C:.:B:.:A ------ C:.:B:.:A
---9.1 ----------- 9.1 ------------ 0.888


Looks like the brand new coils have the lowest values. Also, the shop told me one of my coils was arcing and needed replacement. So... if they all look about the same... does that mean it's more likely the spark plug that is the issue? I have 1 brand new Lead and 1 brand new Trailing spark plug. So if need be, I can update those.

I just want to know if: 1. I'm taking these readings correctly. 2. Are these values normal?

Thanks!

Last edited by Gyro_Bot; 10-04-2014 at 04:24 PM.
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Old 10-04-2014, 04:32 PM
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How do I swap spark plugs without flooding the engine?

Could I do a live plug swap plug and play? ... put all 4 back, but replace #2 coil. Then hope the idle is fine. Leave it on until the engine warms up, and then proceed to do more tests. Could I disconnect #1 and swap the coil - while the engine is on?
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Old 10-04-2014, 06:58 PM
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That worked. The coils where the problem. Mostly one of the two leading coils used for idle.
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