Ignition Coil... from 318 to 325??? Do they break down???

Post Wed Aug 22, 2012 12:51 pm

Hopefully just a quick guys...

Is the ignition coil the same on 318 M40 cars and 325/327 M20 cars???

They look very similar, but all the labels are worn off - I'm hoping to swap the coils between my two cars to try and prove a fault, before BMW rape me for £94.85 (and a 7 day wait!!!) for a new one!!!

Post Wed Aug 22, 2012 1:00 pm

Yes they are the same on M40, M20 and even M30. (most common ones found in scrap yards).

Post Wed Aug 22, 2012 1:51 pm

Perfect, cheers mate!!!

Post Wed Aug 22, 2012 1:52 pm

Hope you are well! Long time no see

Post Wed Aug 22, 2012 3:17 pm

Still surviving!! All the usual - back problems, car problems.....

Deffo need a new coil now though, as i tightened the -ve terminal back up, it snapped off!!!
No idea if they're always that easy to overtighten or if that was the problem i was having!!!

Post Wed Aug 22, 2012 3:27 pm

Just put an ad in the wanted section, but to further the above - is it likely/usual that an ignition coil will break down or be less efficient with age???

Will I be ok running a second hand one, or should I bite the bullet and pay out for a shiny new one???

Without wanting to go through it all here, I was/am getting an intermittent misfire when hot/under load/max throttle, at different/random revs

Post Wed Aug 22, 2012 5:00 pm

Back problems are a total inconvenience, I have dodgy back, for the most part its ok, if I lift something off centre r twist my upper and pick something up it just goes and swells up! Think ill have it for life now

Coils can break down yes, its not normally something that wears, but its a cheap and easy part to rule out, im sure someone will have one for you for sure!

The terminal is an M6 I believe? Thats quite small so under certain conditions its possible for the threads in the terminal to develop micro fractures meaning the stud would snap off very easily.

Post Wed Aug 22, 2012 5:38 pm

My back probs escalated last winter, got a few disc probs, as well as the usual back pains/probs, one of which was trapping a nerve and cutting off my left leg!!!!!
Had an injection to the nerve which seems to have almost sorted that bit, so I'm on the mend, again!!!

Hopefully got a coil located now, but still open to more offers in my wanted thread!!!

Well it looked small, old and a bit crusty and it's now useless!!! Lol!!!

Cheers!!

Post Wed Aug 22, 2012 8:26 pm

ive got a spare, im just off london road,

Post Thu Aug 23, 2012 10:30 am

9818 - you have pm...

Post Thu Aug 23, 2012 10:38 am

Coils usually last years, but do occasionally fail, and sometimes intermittently.

I had a case where the car became increasingly difficult to start. The first thing I did was check for sparks, which there were. However, then the car wouldn't start at all, and having gone through checks of the carb, etc., I was about to remove the cylinder head when I thought I'd check for sparks again - no sparks at all this time round.

Swapped the coil for a spare, and it's been fine ever since.

Post Thu Aug 23, 2012 11:23 am

I've also had another thought...

Obviously, the coil (and therefore the ignition system), is powered by the battery - so what sort of power (voltage/current) do they need to perform at max load???

If there was an electrical prob somewhere, charging/alt/battery, etc, would/could that cause a random intermittent misfire???

Does a coil use more power when the engine is under max load???

I'm assuming it's a constant and it prob needs a fairly low voltage, but just a thought...

Post Thu Aug 23, 2012 12:20 pm

The electronic ignition unit/ECU will need a certain level of power to drive it; usually if the battery voltage drops below about 8-9V, it will start causing problems, such as a weaker spark at the plugs or intermittent dropping out.

Normally, with the engine running and the alternator charging, the voltage across the battery will be around 14V.

With the engine running at high rpm, the coil will be switched on and off more rapidly (higher duty cycle), so yes, it will consume more power than at low rpm.

So, check the engine to body earth strap and that the alternator is charging the battery properly. Also check all connections to the coil.

If you have a multimeter, measure the resistance of the HT leads - they should all be between 3-10 kilohms.

Post Thu Aug 23, 2012 1:01 pm

Ok, ta!!!

Just considering it because I was having a problem every now and again with starting, which seemed to be because the batt didn't have enough juice, and it doesn't ever got to 14v on this car!!!! Was all very strange but has been behaving ok recently.
All earths, etc are new 0 gauge cable!!!

We'll see what happens if i get to connectin my sound system up - that will kill the electrics if there's any little probs lurking!! Lol!!!