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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 09-30-2012, 08:50 AM   #1
Capo-DaDon
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Join Date: Sep 2012
Location: Texas
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My Ride: 325
2002 325i engine misfire

Hi guys, just recently my cars service engine light turned and my car runs rough while Idle and the rpm needle moves up and down. I took it to a mechanic to run a diagnostic test and he told me that I had a misfire in my spark plugs I went ahead and change them all but I still have the same problem. Does anyone know what this problem could be? Or has anyone had the same problem and got it fixed? This seems to be a common problem with the e46 because I've seen a few videos on YouTube with guys with the same problem. Please help and thank you
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Old 09-30-2012, 08:55 AM   #2
Sansho
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Join Date: Jun 2010
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You need to post the error codes being thrown. If you don't have that capability yourself, any Autozone can read them out for you.
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Old 09-30-2012, 09:10 AM   #3
dirtbiker245
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My Ride: 00 323ci, 02 325i
Once you get the error codes, it usually will tell you what cylinder is misfiring. You can then take the coil pack from that cylinder and move it to another cylinder and see if the problem moves from to the "new" cylinder. That way you can find if you have a dead coil and replace it. My 323's coil packs started to hit the can at about 150k miles. I replaced them one by one as they went out but always had a spare sitting in my trunk. lol.

Another way to check coil packs without getting the codes is to start the motor and let it idle. Unplug each coil pack one by one, plug it back in before moving to the next spark plug. When you unplug it, a cylinder that is fine will make the engine rpm drop or possibly stall. The cylinder that is bad will make no difference whether the coil is plugged in or not. Then you know which cylinder is the problem one.

A cylinder needs 3 things to fire.
1. Spark
2. Fuel
3. Compression

You probably have compression but you can always do a compression check if you want. Spark can either be plugs, coils, the wires from the coils to the ECU or the ECU. Most common problem is the plugs and coils.

Fuel could be dirty injector, clogged fuel filter, or bad fuel pump. If It is ONLY misfiring on one cylinder, then that rules out fuel pump and filter. If those are bad it would misfire randomly on all cylinders.

Dirty injector is a possibility, but not super likely. Usually on these cars the problem lies in spark.

Good luck diagnosing!

Last edited by dirtbiker245; 09-30-2012 at 09:17 AM.
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Old 09-30-2012, 09:31 AM   #4
Capo-DaDon
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Thanks guys I appreciate it
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