48i cold start problem?

[absentmathis]

The past two days have been colder than normal for winter in Charlotte, at least this year...mid 20s. My 08 48i has been hard to start two mornings in a row. The battery is a little bit older but it cranks really strong and shows no other signs of weakness, and after 30-60 seconds or so of cranking (on and off) it will start, sputter and die, and then eventually start and run perfectly. Plugs are a couple years old, the car is pretty well maintained with no obvious issues or codes from a Carly scan. After getting it started the past two mornings it’s run and started perfectly the rest of the day. Even after sitting for hours. Any ideas on this?

[dadysev]

Any codes? do you see black smoke out the back when it does start? If so leaky injectors.

[absentmathis]

No smoke at all that I can tell. Are leaky injectors an issue on the gas V8s? Hadn’t previously heard that but they may be. No codes at first, got couple misfires on second scan but that seems like a side effect more than a cause due to the stumbling at start. I’m wondering about fuel pressure. And also the battery because I know how sensitive these things are, but just have a hard time believing the battery is the problem if it can crank the car easily for long enough that it starts.

Edit to add: the misfire codes were cleared after morning cold start and didn’t return all day.

[ard]

Originally Posted by absentmathis

No smoke at all that I can tell. Are leaky injectors an issue on the gas V8s? Hadn’t previously heard that but they may be. No codes at first, got couple misfires on second scan but that seems like a side effect more than a cause due to the stumbling at start. I’m wondering about fuel pressure. And also the battery because I know how sensitive these things are, but just have a hard time believing the battery is the problem if it can crank the car easily for long enough that it starts.

Edit to add: the misfire codes were cleared after morning cold start and didn’t return all day.

Battery.


The 'smart' battery management system is conserving battery current for the starter, but at the cost of starving other components (hence the misfires and stumbling).


It can surely be surprising, since in the good old days, there was one +12V wire, and if there was power to crnk there was power to start- but no so much these days.


Thats my vote!

[absentmathis]

Hey ard, appreciate the input. I’d second your vote on most issues, and funny enough I bought a battery earlier tonight (pickup tomorrow) because of this and it’s time anyway. Got a Bosch 49-850 for $150. Is the autocraft better?

[dadysev]

Originally Posted by ard

Battery.


The 'smart' battery management system is conserving battery current for the starter, but at the cost of starving other components (hence the misfires and stumbling).


It can surely be surprising, since in the good old days, there was one +12V wire, and if there was power to crnk there was power to start- but no so much these days.


Thats my vote!

Forgot about that depending on where you live. These BMW's are heavily dependent on stable voltage of just over 12v. On my 11' 550i i had to deregister my battery to get rid of a lot of gremlins. I don't drive it that often and it has that stupid "efficiency dynamics" which only charges when you decelerate, so no short trips!

I'm having an issue similar to yours with my 4.8. I know its vanos related though as i just changed all 4 vans solenoids and got back my power, but on cold days its like the bank 2 intake vans is sticking or not getting enough oil pressure to move the cam and advance the timing so i get the code p0021.
when it starts it takes a bit longer and then 5 seconds later you hear the engine rev up to 1500 for a second and then come down. if i don't tap the throttle it may throw the code. if i turn it off an on again its all good. Driving me nuts!

Good luck with yours!
BTW, multiple missfires on these n62's and even m52's can be vanos related sometimes also, but you really need to scan after the battery is changed.