Just bought first e46 m3, looking for help! UPDATE

[Htown86er]

It failed to start, so how the batt got 12.8v? Don't let us guessing. The more info data input, the faster you get help.

I dont know how it failed to start, it measure 12.8, when i turn ignition it drops. But everything in the car has perfect power.

[elrichmeister]

So youre having an intermittent starting issue, with no crank? Its either going to be the starter or an EWS issue.
Here is a great resource to a "no start" guide

https://www.e46fanatics.com/threads/no-start-guide.1011677/

[Nate047]

I have the same / very similar issue on my car, intermittent no start. It only happens on my car after it's been driven and brought up to temp, otherwise I could never come up with a pattern.

It's on my "to do" list, but I have a little hand held jumper box thing I always keep in my car, I just use that when it happens instead of fixing it because of how I am as a person.

[sapote]

I dont know how it failed to start, it measure 12.8, when i turn ignition it drops. But everything in the car has perfect power.

is it a standard lead-acid batt? if it is then no way with a car failed to start and the batt still has 12.8v after a few days from fully charged up.

[sapote]

I have the same / very similar issue on my car, intermittent no start. It only happens on my car after it's been driven and brought up to temp, otherwise I could never come up with a pattern.

It's on my "to do" list, but I have a little hand held jumper box thing I always keep in my car, I just use that when it happens instead of fixing it because of how I am as a person.

it failed to crank or it cranked but not fire up?

[Nate047]

it failed to crank or it cranked but not fire up?

Complete loss of power in the car, no crank, no lights, nothing.

[sapote]

I have the same / very similar issue on my car, intermittent no start. It only happens on my car after it's been driven and brought up to temp, otherwise I could never come up with a pattern.

This's so weird, like the alt not charging the batt and you had used up the batt to the point the system shut down due to too low voltage. For this, I'm surprised that the portable booster could start the engine. To really know what happened, need to measure the batt volt when engine died.
So after using the booster to start up, car ran normal with minimum idling needed to charge up the batt?

[Nate047]

This's so weird, like the alt not charging the batt and you had used up the batt to the point the system shut down due to too low voltage. For this, I'm surprised that the portable booster could start the engine. To really know what happened, need to measure the batt volt when engine died.
So after using the booster to start up, car ran normal with minimum idling needed to charge up the batt?

Yea super odd right? It would run normally after jumping it, and usually the issue would go away for a week or two between, then happen again. I can’t drive the car right now unfortunately, but I’d like to circle back on this later when I can diagnose it properly.

[sapote]

Yeah, measure the jumper posts voltage and battery voltage when engine shut down again.