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      05-06-2021, 11:43 PM   #1
WrxToBeamerGuy
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Ignition Coil Primary and Secondary Resistance?

BMW 340i xDrive 2016 I'm in the US.

Anyone know a good set of procedures for this car or would generic advice from google do the job? I want to use my Ohm meter to check each of the coils to make sure they are functioning correctly.
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      05-07-2021, 10:12 AM   #2
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Use an OBD reader and check for misfires. if there are none, then it's probably safe to assume their functioning ok.

Do you have a reason to believe they are not?
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      05-07-2021, 10:18 AM   #3
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Checking for misfires is the best method. Resistance won't help you if the insulation is breaking down in the coil, and they are arcing under use.
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      05-07-2021, 10:21 AM   #4
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I am interested in this as well as I have codes 113026 relay ignition, supply voltage injection: short circuit to ground/119404 rail sensor, signal: fixed lying/ 1F0514 Valvetronic, supply voltage: Short circuit to ground. I was told that its possible a bad coil could result in these codes so knowing how to do what the OP is asking would be very helpful!
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      05-07-2021, 10:33 PM   #5
WrxToBeamerGuy
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Quote:
Originally Posted by ooshnoo View Post
Use an OBD reader and check for misfires. if there are none, then it's probably safe to assume their functioning ok.

Do you have a reason to believe they are not?
I'm having trouble with it so I dont want to turn it on. I was having misfires and also I think an injector is stuck open.
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      05-07-2021, 10:34 PM   #6
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Quote:
Originally Posted by Wires View Post
Checking for misfires is the best method. Resistance won't help you if the insulation is breaking down in the coil, and they are arcing under use.
well my plan is to check all coils primary and secondary winding resistance and see if they match. Is that a good plan?
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      05-08-2021, 08:07 AM   #7
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I'd check for codes first. The DME will trap errors on coils not functioning properly, misfires, etc.

You can just pull out one of the good coils and compare to your suspected bad one if you are looking to validate resistance. I'm just saying I've seen in high voltage devices like this where they test fine on the bench, apply power and they arc inside.
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      05-08-2021, 08:24 AM   #8
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Quote:
Originally Posted by Wires View Post
Resistance won't help you if the insulation is breaking down in the coil, and they are arcing under use.
If the insulation is breaking down there will be leakage from winding to winding, which would be seen as lower resistance than normal. Misfires can be caused by other factors as well, so if you have misfires doing a resistance test of the coils would help to confirm or rule them out as a potential cause. I haven't come across the exact primary/secondary values, but the primary resistance is listed as less than 600 megohms, with the primary to secondary resistance ratio being 1:80.
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      05-08-2021, 10:32 AM   #9
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Quote:
Originally Posted by Billfitz View Post
If the insulation is breaking down there will be leakage from winding to winding, which would be seen as lower resistance than normal. Misfires can be caused by other factors as well, so if you have misfires doing a resistance test of the coils would help to confirm or rule them out as a potential cause. I haven't come across the exact primary/secondary values, but the primary resistance is listed as less than 600 megohms, with the primary to secondary resistance ratio being 1:80.
Leakage yes, but that isn't typically picked up on with an Ohmmeter. If you had access to an inductance meeting, it would show there. Regardless, you do have 5 other coils to benchmark against if measuring resistance is the plan.
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      05-08-2021, 10:49 AM   #10
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I've enough experience with inductors and transformers in audio to know that when you have a winding to winding short due to cooked insulation you can measure the change in both the inductance and resistance, and capacitance too for that matter. However, I agree that trying to find out what the spec resistance for the coils is doesn't matter when you can simply pull and measure all of them and compare the results.
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      05-08-2021, 12:27 PM   #11
WrxToBeamerGuy
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Quote:
Originally Posted by Billfitz View Post
If the insulation is breaking down there will be leakage from winding to winding, which would be seen as lower resistance than normal. Misfires can be caused by other factors as well, so if you have misfires doing a resistance test of the coils would help to confirm or rule them out as a potential cause. I haven't come across the exact primary/secondary values, but the primary resistance is listed as less than 600 megohms, with the primary to secondary resistance ratio being 1:80.
it's in milliohms not megohms

Primary resistance less than 600 mΩ
Ratio, primary coil to secondary coil 1:80

but this is still helpful information. So 1:80 would mean im looking for 48 Ohms on the secondary coil?

That being said I'll just pull and compare all results.
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      05-08-2021, 12:37 PM   #12
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      05-08-2021, 11:18 PM   #13
WrxToBeamerGuy
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Just an update for everyone I set my ohm meter to 200 ohms and read the readings and got .4 - .5 ohms off of each primary winding so under the 600 milliohm requirement.

I could not however figure out how to get any sort of secondary winding reading.
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