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I have a 2003 m3 e46. Last year I replaced all the coils. A few weeks ago I replaced the thermostat and wsterpump. Its been running ok since. Today my CEL came on, red the codes and cylinder 3 is misfiring. When driving it will randomly stop misfiring and run perfectly fine, then go back to running poorly. I replaced the coil on that cylinder and same thing happens. Any ideas?
 

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Could be a bad fuel injector
 

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Classic trick is to move coil 4 to hole 3 and see if the misfire moves. If it doesn't move, the problem is NOT the coil. Look at injector, vacuum leak, bad plug, compression test, etc., etc.,
 

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I have a 2003 m3 e46. Last year I replaced all the coils. A few weeks ago I replaced the thermostat and wsterpump. Its been running ok since. Today my CEL came on, red the codes and cylinder 3 is misfiring. When driving it will randomly stop misfiring and run perfectly fine, then go back to running poorly. I replaced the coil on that cylinder and same thing happens. Any ideas?
Consider replacement with FCP Euro sourced coils. Lifetime guarantee
 

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E30M3 Race F10 535 R1150Rt M Coupe
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The classic route of tracing down a misfire is thus:

Move offending cylinder ignition coil to another cylinder. Did the misfire move? Bad coil.
If not, swap two spark plugs. Did the misfire move? Bad spark plug.
Still present? Swap two fuel injectors. Did the misfire move? Bad /dirty injector.
 
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