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Old 09-14-2012, 10:18 PM   #1
bboyjamin
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Ignition Coil Test

Hi All, this is my first post.

I've got a 2007 2.0 L Focus. It died while driving. Found the Engine Management Fuse, F9, 20A, was bad. Replaced that and it started.

After starting I noticed it was idling rough. It wasn't really noticeable when driving, but the engine is shook around a lot on idle. I guess it's a misfire.

I checked resistance on all 4 coils (coil on plug system).

I assumed primary resistance is measured between the two connector pins, and secondary is measured between the bottom coil and one of the connector pins.

RESULTS:

1 (passenger side): primary 3.1 Ohm, secondary 5.6 kOhm
2: primary 3.1 Ohm, secondary 5.5 kOhm
3: primary 3 Ohm, secondary 5.4 kOhm
4 (driver side): primary 4.2 Ohm, secondary O.L. (aka open loop)

The haynes manual is a little lacking on the 2005 and later electrical stuff. It says resistance should be: primary 0.4 - 0.6 Ohm, secondary 10.5 - 16.5kOhm.

I'm inclined to believe that the Haynes is wrong and my readings for cylinders 1 - 3 are the true resitances.

My coil part number is 4M5G-12A366-BC , 6B1182

Right now my suspicion is that coil 4 is toast. At over $100 per coil, I thought I'd tell my story and let someone point out any flaws in my test.



p.s. I looked at all spark plugs as well and each one is just a little brown. Looks OK.



Thanks all.


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Old 09-14-2012, 11:03 PM   #2
VEGAS
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i dunno a 100% answer but sounds like you did it right... I wish you were in Vegas, I have a spare..
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Old 09-18-2012, 10:37 PM   #3
bboyjamin
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Thanks Vegas, Got one new coil from Ford today, installed it and she's running better than ever.

I've heard coil on plug is more reliable cause there are no spark plug wires. But they're so expensive! This coil was $190 from the dealership. That would be almost $800 if I bought 4 OEM coils.

Anyway, I'm happy for now!
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Old 09-19-2012, 02:58 AM   #4
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eBay is dirt cheap and most people here who tinker have spares.
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