BMW E46 - Spark Plug Coils - One down all down! | Technical matters | Back Room Forum

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Sat 21 Jan 2012 19:16

BMW E46 - Spark Plug Coils - One down all down! - meldrew

My wifes car had been a bit "iffy" but nothing one could put a finger on. At 80k miles probably the HJ seven year life syndrome.

Last Thursday it fired up clearly on less than four cylinders and a warning light (as if one was needed!) came on.

Chugged to my local garage (we have a couple of awesome non franchised repairers where I live) who identified the problem immediately.

Alas with one dead coil it could not be replaced just itself without the ECU taking an outright dislike to it! All four were replaced and it now runs like new.

Question: Why can't just the one be replaced and is this a problem on all cars nowadays? They were originally replaced under warranty so have probably only lasted 60k miles.

Edited by meldrew on 21/01/2012 at 19:17

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Sat 21 Jan 2012 20:27

BMW E46 - Spark Plug Coils - One down all down! - elekie&a/c doctor

Most modern petrol engines use this design of "coil over plug" .Unfortunately due to the location of the coil ,in the very hot part of the cylinder head,with no air space around them for cooling,tends to make them fail on a regular basis.Renault ,VW and Bmw seem to be the worse culprits.It is possible to replace just the one faulty coil but I think most garages would recommend replace all due to amount of labour reqd .It can take the same to replace 1 or X many.Also I would suggest if one has failed then the others are probably not far behind.Btw,I have seen coils fail on Bmw just out of warranty on 08 plates.hth

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Fri 27 Jan 2012 20:43

BMW E46 - Spark Plug Coils - One down all down! - meldrew

Thanks for helpful comments. Yes it does make sense to change them all (4 coils and plugs = £205 incl VAT) and I hope this lasts until car change at 100k miles in a years time!

For the record we had this failure originally when the car was only a few months old and all were replaced under warranty.

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Fri 27 Jan 2012 21:59

BMW E46 - Spark Plug Coils - One down all down! - xtrailman

I wouldnt change all four. Electronic components dont all fail at the same time.

When i had a Audi in 2000 lots of these head mounted coils were failing, but due to a component problem.

Audi were only changing the faulty coil, not all four.

In four years none of mine failed.

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