Ignition Coil Readings
#1
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Ignition Coil Readings
So does anyone know what a good measurement is for our ignition coils? I thought I had some bad readings, so I ordered a new set of coils. I measured them, and they might be similar readings to my used ones (I'll check once I swap them out).
I did find a very strange thing thou. The readings are different depending on the resistance measurement mode I use on my multimeter. The 2000 ohm (diode) measurement setting gives very different results. If anyone understands electronics, and/or ignition coils better they can explain it.
For reference, I'm including a picture of the meter I used (a cheap one, but seems to read fairly well on other things) and the readings of all four new coils. I did both forward and reverse readings on the terminals, the first letter I list is the terminal which the positive lead was attached to. For the readings in Mohm, the value was steadily dropping, after a few seconds it would drop very slowly and that was the reading I took. All other values were stable. Unless it was the 2000ohm diode setting, all other modes would read the same value. The mode listed provided the most accurate reading.
A-B (20K res) : 1.54Kohm, 1.42Kohm, 1.38Kohm, 1.56Kohm
A-B (2000 diode) : 745ohm, 713ohm, 701ohm, 755 ohm
B-C (20M res) : 16.2Mohm, 18.6Mohm, 18.2Mohm, 16.5Mohm
B-C (2000 diode) : 487ohm, 495ohm, 495ohm, 494ohm
C-A (20M res) : inf, inf, inf, inf
C-A (2000 diode) : inf, inf, inf, inf
reverse readings
B-A (20K res) : 1.57Kohm, 1.43Kohm, 1.39Kohm, 1.57Kohm
B-A (2000 diode) : 577ohm, 575ohm, 575ohm, 573ohm
C-B (20M res) : inf, inf, inf, inf
C-B (2000 diode) : inf, inf, inf, inf
A-C (20M res) : 14.6Mohm, 17.6Mohm, 17.2Mohm, 15.6Mohm
A-C (2000 diode) : 572ohm, 570ohm, 565ohm, 570ohm
I did find a very strange thing thou. The readings are different depending on the resistance measurement mode I use on my multimeter. The 2000 ohm (diode) measurement setting gives very different results. If anyone understands electronics, and/or ignition coils better they can explain it.
For reference, I'm including a picture of the meter I used (a cheap one, but seems to read fairly well on other things) and the readings of all four new coils. I did both forward and reverse readings on the terminals, the first letter I list is the terminal which the positive lead was attached to. For the readings in Mohm, the value was steadily dropping, after a few seconds it would drop very slowly and that was the reading I took. All other values were stable. Unless it was the 2000ohm diode setting, all other modes would read the same value. The mode listed provided the most accurate reading.
A-B (20K res) : 1.54Kohm, 1.42Kohm, 1.38Kohm, 1.56Kohm
A-B (2000 diode) : 745ohm, 713ohm, 701ohm, 755 ohm
B-C (20M res) : 16.2Mohm, 18.6Mohm, 18.2Mohm, 16.5Mohm
B-C (2000 diode) : 487ohm, 495ohm, 495ohm, 494ohm
C-A (20M res) : inf, inf, inf, inf
C-A (2000 diode) : inf, inf, inf, inf
reverse readings
B-A (20K res) : 1.57Kohm, 1.43Kohm, 1.39Kohm, 1.57Kohm
B-A (2000 diode) : 577ohm, 575ohm, 575ohm, 573ohm
C-B (20M res) : inf, inf, inf, inf
C-B (2000 diode) : inf, inf, inf, inf
A-C (20M res) : 14.6Mohm, 17.6Mohm, 17.2Mohm, 15.6Mohm
A-C (2000 diode) : 572ohm, 570ohm, 565ohm, 570ohm
#2
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Thread Starter
Well, it looks like my coils were probably fine. These are the measurements taken from my old (I believe original, 45k mile) coils.
A-B (20K res) : 1.71Kohm, 1.71Kohm, 1.73Kohm, 1.75Kohm
A-B (2000 diode) : 788ohm, 810ohm, 799ohm, 805 ohm
B-C (20M res) : 15.5Mohm, 15.1Mohm, 15.2Mohm, 14.9Mohm
B-C (2000 diode) : 486ohm, 486ohm, 488ohm, 485ohm
C-A (20M res) : inf, inf, inf, inf
C-A (2000 diode) : inf, inf, inf, inf
reverse readings
B-A (20K res) : 1.72Kohm, 1.72Kohm, 1.74Kohm, 1.76Kohm
B-A (2000 diode) : 579ohm, 577ohm, 574ohm, 573ohm
C-B (20M res) : inf, inf, inf, inf
C-B (2000 diode) : inf, inf, inf, inf
A-C (20M res) : 14.6Mohm, 14.5Mohm, 14.6Mohm, 14.1Mohm
A-C (2000 diode) : 582ohm, 583ohm, 578ohm, 581ohm
These look about the same as the new ones. So, when people say that their readings show the coils are going, what are they measuring and what values are they seeing?
A-B (20K res) : 1.71Kohm, 1.71Kohm, 1.73Kohm, 1.75Kohm
A-B (2000 diode) : 788ohm, 810ohm, 799ohm, 805 ohm
B-C (20M res) : 15.5Mohm, 15.1Mohm, 15.2Mohm, 14.9Mohm
B-C (2000 diode) : 486ohm, 486ohm, 488ohm, 485ohm
C-A (20M res) : inf, inf, inf, inf
C-A (2000 diode) : inf, inf, inf, inf
reverse readings
B-A (20K res) : 1.72Kohm, 1.72Kohm, 1.74Kohm, 1.76Kohm
B-A (2000 diode) : 579ohm, 577ohm, 574ohm, 573ohm
C-B (20M res) : inf, inf, inf, inf
C-B (2000 diode) : inf, inf, inf, inf
A-C (20M res) : 14.6Mohm, 14.5Mohm, 14.6Mohm, 14.1Mohm
A-C (2000 diode) : 582ohm, 583ohm, 578ohm, 581ohm
These look about the same as the new ones. So, when people say that their readings show the coils are going, what are they measuring and what values are they seeing?
#4
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iTrader: (2)
@ dannobre ... looks like I'm following you around lol
Service Bulletin for Ignition Coil inspection
http://www.finishlineperformance.com...16-07-1793.pdf
My quick review of it, didn't mention anything about measuring the ohms ...
Service Bulletin for Ignition Coil inspection
http://www.finishlineperformance.com...16-07-1793.pdf
My quick review of it, didn't mention anything about measuring the ohms ...
Last edited by wcs; 05-22-2010 at 06:16 AM.
#5
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Thread Starter
@ dannobre ... looks like I'm following you around lol
Service Bulletin for Ignition Coil inspection
http://www.finishlineperformance.com...16-07-1793.pdf
My quick review of it, didn't mention anything about measuring the ohms ...
Service Bulletin for Ignition Coil inspection
http://www.finishlineperformance.com...16-07-1793.pdf
My quick review of it, didn't mention anything about measuring the ohms ...
#8
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So it looks like it probably wasn't the coils. I took it in to the dealer, and after a decarbonization and some other attemped fixes, nothing changed. A compression test revealed low numbers across the board.
It took a while for them to determine if the engine would be replaced under warranty, but they eventually decided that it would be, and it's currently being swapped. I had to supply proof of service, even for the period before I owned the car. Luckily the previous owner did their service at a Mazda dealer so I was able to obtain the records. Not sure what would have happened otherwise.
It took a while for them to determine if the engine would be replaced under warranty, but they eventually decided that it would be, and it's currently being swapped. I had to supply proof of service, even for the period before I owned the car. Luckily the previous owner did their service at a Mazda dealer so I was able to obtain the records. Not sure what would have happened otherwise.
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