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Join Date: Sep 2005
Location: Sacramento CA
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e46 Coil Resistance Spec?

Just about to change the plugs on the 2004 330.

I understand that a lot of e46 coils failed and were replaced on warranty. This car has recently developed a couple of quirks that may be coil related, so I want to check the coil resistance while I have them off.

I have not dropped the $90 for a manual for this car yet.

Anyone have the resistance specs for these coils?
Any other tests I can do while they are off?
Should they be hot when I check the resistance?

Thanks!
Old 09-09-2008, 09:02 PM
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Location: DFW (Hurst), Texas
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There was a recall or TSB on coils from some of the early E46's but that was taken care of by the 2001 models.

I dont have my E46 manual with me. I've seen people post resistance specs in these forums but they may have been in the E36 forum.

Other things to check are oil in the wells and general condition of the plugs. And don't forget to replace the little ground wires on the coils when you reinstall them.
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Old 09-10-2008, 07:13 AM
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I put in new NGK plugs today. The original BMW (NGK) platinum plugs were eroded around the center electrode a lot more than I would have expected at 62k miles with platinum plugs. If I can figure out a way to make my camera focus through a magnifying glass, I will post a pic.

Measuring the resistance in the coils was interesting.

The primary side had exactly 0.6 ohms resistance on each coil. That sounds reasonable because the spec for an e36 coil is 0.4 - 0.8 ohms.

I did not pull off the spark plug connectors because I didn't want to loosen them. Therefore, my secondary resistance measurement includes the resistance of the connector, which should be 1.8k ohms, according to the parts book.

My cheap digital VOM would not measure any resistance at all on the secondaries. It just was not pushing enough voltage to get any measurable amount of current through the coil. It showed infinite resistance on all of them.

Old reliable analog meter measured 20k ohms on every secondary. Interestingly, however, there appears to be a diode inside the coil, because I measured 20k one way, and infinity the other on all six coils.
Old 09-20-2008, 02:18 PM
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