Starting problems

[Eflynn46]

Hi guys,i’ve had my m3 for about 4 months,i’ve done 4k miles without a problem,this morning i drove to work about 20 mins stopped for a coffee and it wouldnt start.a tow truck came so we tried to jump it,it started,as soon as the jump pack came off it died.the driver stated he can tell the alternator was charging.I took the batt to 2 different places and its good?(sorry for the book trying to give backstory)now its dead in my drive wont start no audible click from the start button.thanks in advance to anyone who can help thanks😩

[Shiza]

Sounds like a bad alternator to me

[Adriano917]

Time to get that $300 alternator and diy.

[Eflynn46]

Hi thanks for responding,i thought the same but with that wouldnt the car start and run til the batt was dead?the tricky part to me was it cranked over with the jump pack

[Eflynn46]

I actually thought starter until it turned over with the jump pack,

[Shiza]

Originally Posted by Eflynn46

Hi thanks for responding,i thought the same but with that wouldnt the car start and run til the batt was dead?the tricky part to me was it cranked over with the jump pack

The jump box was enough to get the car started but if the alternator wasn't charging the battery then yes it will eventually die and leave you stranded like it did.

[Adriano917]

these cars have a lot of modules that need power, just the battery alone won't suffice. check the battery with a DVOM vehicle off, then check the battery again with vehicle running, if the Voltage fluctuates Alternator is working if not more than likely Alternator is kaputt.

[Eflynn46]

The batt was tested by 2 places and it was fine,with that wouldnt the car at least turn over ?i dont see how an alternator would hinder the car turning over with a good batt i prob wasnt clear all the lights,radio,nav all fine

[Adriano917]

after the fact the battery was tested and it was good ?

[Eflynn46]

Yes,but it still wont turn over thats why i was thinking starter til it turned over with the jump pack.i am thinking now starter and the jump pack gave it enough to crank the starter,but i’m thinking it would have stayed running?thanks for your replies

[mapster37]

normally if u a jump start with a booster pack and it starts your battery is faulty. if the engine dies as soon as jumper is removed your alternator is bad. replace alternator and battery and dont forget to register battery replacement

[ItsGary]

check negative terminal for battery build date
Mine says
49
12

Meaning 49th week of 2012 it was produced.

[Eflynn46]

Thanks for responding itsgary,i’ve been reading your posts for months and it seems you really know your stuff about these cars,the battery was replaced by the dealer when i picked the car up from the dealer first week of march,with that it is a delco batt,a buddy that owns a garage seems to think the battery has a dead cell,so it would check out fine until an actual load is put on it,so should i start throwing batteries and alternators and starters at this problem?looking like yes,either way thanks for your insight,typical i wait 4 yrs to buy a car and it dies 2 days before my 11 yr old and i take it to lime rock for the imsa race guess we are driving the accord..yippee??

[ItsGary]

Originally Posted by Eflynn46

Thanks for responding itsgary,i’ve been reading your posts for months and it seems you really know your stuff about these cars,the battery was replaced by the dealer when i picked the car up from the dealer first week of march,with that it is a delco batt,a buddy that owns a garage seems to think the battery has a dead cell,so it would check out fine until an actual load is put on it,so should i start throwing batteries and alternators and starters at this problem?looking like yes,either way thanks for your insight,typical i wait 4 yrs to buy a car and it dies 2 days before my 11 yr old and i take it to lime rock for the imsa race guess we are driving the accord..yippee??

You could always post your codes. The alternator will throw this code if its gone bad

278D BSD, Alternator : Missing

If you need to replace the battery its a Group 49 or an H8 AGM

[Eflynn46]

So now i’m thinking change the batt because the jump pack started it then the alternator because it wouldnt stay running when the jump pack was removed and go from there?it just seemed a little strange that both went together,i was thinking it was something more than that

[Eflynn46]

I never said before no codes at all,i have read enough here to expect some weirdness with a bad battery

[Eflynn46]

I’m grabbing an interstate battery on the way home today i’ll keep you posted and thank you your insight is greatly appreciated!!

[ItsGary]

Can't really help you over the internet much. Like others have said, get the battery tested.

Possibly the battery the dealer gave you could be under manufacturer warranty still?

[pbonsalb]

Also check the ground cable under the car from the oil pan to frame rail by the header collector on the drivers side. Give it a tug to make sure it is not disintegrating. Or since your battery is fine, use a set of jumper cables to make 2 more grounds from the engine block to the chassis and then try starting as normal.

[Eflynn46]

I was wondering if the jump pack being grounded itself had something to do with it.i’m def new to this platform but this is starting to make sense before i start throwing parts at it,possibly the jump pack being grounded let the starter engage?thanks alot i’m going to try this when i get home,is this something that has happened to your car personally or were you involved with another thread?wondering about a possible part number if you had already done it?again thanks for the insight the people on this forum are 😎

[Dpc2u]

If you are not sure if they have already done so have the battery load tested. That simulates the load placed on it under a start attempt. If the voltage drops a more than just a little, you have a weak or bad cell. Also clean the inside of the terminals. Just a little bit of corrosion will cause issues under a load.

[Eflynn46]

Thanks for the replies looks like i have some homework today hopefully i can get it up and running my son was very upset we weren’t driving our m to lime rock today we have been looking forward to it since the day it came home,the thought of driving our accord there again is killing us