Hi,

Anyone have any ideas why a N52 engine would stall under hard braking , at random times?

Not always under braking it would stall, But when it does stall, The only way to get the car back to start is to get a jump-start.

On the forms, it someone say it is a sign of a failing brakes booster/vacuum leak,. But would having that result in the car not being able to start without getting a jump after the stall?

 

Next time it does it, before getting a boost try starting it as if it's flooded (press gas pedal to the floor and hold). Sounds like you're overfuelling for some reason. And get your codes read out.

 

Will get codes tomorrow, But I tried that method as well pressing - the gas pedal to floor and still no start. It sounds like it wants to start, but doesn't.

 

the only thing a jump start brings to the scenario is your own battery or other parts of the battery/charging system is too weak to restart it again.

Perhaps getting a high compression situation for some reason and the battery can't overcome it? and the high compression is also what causes the stall?

 

Need more details of your car, like year, model and manual or auto transmission?
What really happens when you can't start after stall?
Engine not turn over or when you try to start??
Also got,any faultcodes after stall?

 

same thing is happening to my 2008 535i

only when cold it would try to stall when braking hard and sometimes it would actually stall

but mine restarts right up. no codes.

 

Try this diagnostic test:

With the engine running at idle, Remove the oil filler cap.

Is it REALLY hard to remove? (due to a lot of vacuum)

After you remove it, does the engine start to idle roughly?

 

ok did this test and everything was fine.

wasn't hard to remove and there was no rough idle with the oil filler cap opened.

i have the RB PCV valve, i don't know if that changes anything. And no aftermarket catch can.