Roasting ignition coil

Post Sat Aug 01, 2015 7:14 pm

I've got a E30 318i m40 and the ignition coil is f00kin hot after running for 15 mins. Is this normal or do I have a problem?

Post Sat Aug 01, 2015 9:57 pm

They run warm, but I wouldn't say 'hot'.

Post Sat Aug 01, 2015 10:33 pm

mmm.... if u think u need another ,ive got 1 avail , £16 posted.

Post Sun Aug 02, 2015 11:08 pm

Just fitted a good used one, the old one cracked I'm assuming this was due to the coil getting so hot. Can anyone share some info on this im pretty confused

Post Sun Aug 02, 2015 11:46 pm

Is the replacement running cooler?

Post Mon Aug 03, 2015 12:02 am

Nope it's still running hot

Post Mon Aug 03, 2015 9:36 am

In that case I'd suspect an ECU fault - either the coil driver gone leaky, or a fault in the components driving it, keeping it turned partly on all of the time.
Is the ECU running particularly hot?
Does the coil get warm if the ignition is left turned on without the engine running?

Post Mon Aug 03, 2015 7:38 pm

What do you mean by this "Either the coil driver gone leaky, or a fault in the components driving it, keeping it turned partly on all of the time."

Yes the ECU also runs very hot didnt really think anything of it until you told me. Also I left the ignition on for about 5 mins and the coil isnt getting hot.

Is it worth me taking the cover off the ECU and looking inside to see if there is any corrosion or any heat marks on the circuit board?

BTW a fitted a good second hand alternator last year.

Post Mon Aug 03, 2015 9:16 pm

SAP1 wrote:What do you mean by this "Either the coil driver gone leaky, or a fault in the components driving it, keeping it turned partly on all of the time."

It basically means try a fresh ECU. The problem is more likely to be actual component failure, rather than something like a dry joint. It's rare, but I'm surprised it's not more common when I read on here of people pulling spark plug leads off on a running engine. If the spark plug gap isn't there for the energy to jump across, then it's likely to flash over internally in the coil, and send a pulse of a few tens of thousands of volts back into the coil driver in the ECU.

Post Thu Sep 10, 2015 7:47 pm

Here's a bit of an update, so I have replaced the ECU and now the coil isn't getting hot and the ECU is luke warm so all is good.

But now the car seems to be lumpy on idle. It runs fine and then the engine shudders slightly and then does this over and over again.

Any reason why this is doing this?

Post Thu Sep 10, 2015 8:38 pm

Leaky driver it looks like it was then!
What you're describing is characteristic of a weak mixture at idle (air leaks, worn injectors, etc.), but don't forget that the fresh ECU may need a bit of time to learn the idle settings.

Post Fri Sep 11, 2015 11:52 am

SAP1 wrote:Here's a bit of an update, so I have replaced the ECU and now the coil isn't getting hot and the ECU is luke warm so all is good.

But now the car seems to be lumpy on idle. It runs fine and then the engine shudders slightly and then does this over and over again.

Any reason why this is doing this?

I thought you were a BMW master tech with 30 years experience?

Post Fri Sep 11, 2015 1:28 pm

LOL mate that's my dad, I'm 18 but have a huge love for E30s

And I try to do most of the work myself without my dads help