[bhavyas]

So for the past few days I am noticing something about my exhaust when I first start up the car..

On some days the sound is very feeble, like a small "grrrr" nothing monstrous... but on some days it starts up with a crazy monstrous sound, enough to cause vibrations in my apt. I keep mine in Sports mode., but its just unpredicatble.

Not sure if this an issue but anyone else notice something like this happening?

[Sledgehammer70]

Are you noticing what drive mode the car is starting in? If I am in track mode, my car will default to Tour mode when i shut it off and start it back up again. But when in Sport mode, it will always stay in sport mode.

Not sure if this is a ECU bug or how the car should work, but sounds like your car is on tour sometimes and that is why it is tame.

[Modshack]

I leave mine in sport mode and it always starts with a growl.
If I start in Tour mode, the same growl, but it calms down in a few minutes when the valves close..

[raptor5244]

Originally Posted by bhavyas

So for the past few days I am noticing something about my exhaust when I first start up the car..

On some days the sound is very feeble, like a small "grrrr" nothing monstrous... but on some days it starts up with a crazy monstrous sound, enough to cause vibrations in my apt. I keep mine in Sports mode., but its just unpredicatble.

Not sure if this an issue but anyone else notice something like this happening?

Cold start or warm start?

[JRS]

If your car starts up cold the computer has the timing set pretty far retarded which makes a lot more exhaust noise. It's programmed to tapper off towards normal timing within 1 minute regardless of the mode the cars in. I can post some pic's of the computers parameters.

[bhavyas]

Originally Posted by Nicul15

ambient air tempurature plays a big part in the cold start

I noticed a bigger growl when I start my car after a few days... So say.. If I start my car on a Saturday after not starting it up since last sunday... The growl is louder.. The followin day ..That is sunday.. If I start my car... It's more feeble..

[bhavyas]

Originally Posted by Sledgehammer70

Are you noticing what drive mode the car is starting in? If I am in track mode, my car will default to Tour mode when i shut it off and start it back up again. But when in Sport mode, it will always stay in sport mode.

Not sure if this is a ECU bug or how the car should work, but sounds like your car is on tour sometimes and that is why it is tame.

I keep my car in sports mode always.. Not sure how to test it for the ecu bug

[bhavyas]

Originally Posted by JRS

If your car starts up cold the computer has the timing set pretty far retarded which makes a lot more exhaust noise. It's programmed to tapper off towards normal timing within 1 minute regardless of the mode the cars in. I can post some pic's of the computers parameters.

Interesting... Sure can you post some pics.. Also it would be great if u I can explain what it means..lol

[raptor5244]

Originally Posted by bhavyas

I noticed a bigger growl when I start my car after a few days... So say.. If I start my car on a Saturday after not starting it up since last sunday... The growl is louder.. The followin day ..That is sunday.. If I start my car... It's more feeble..

Yeah, that is pretty typical. Like JRS mentioned the ECU has to use all its sensors to manage the fuel injection process. If the engine is cold you need more fuel, timing changes, higher idle rpm and you run in open loop mode for a bit until the O2 sensors warm up enough before the ECU switches to closed loop. You will then notice the idle come down and things quiet down a bit into a nice exhaust burble. So, if you engine is still warm when you go to start it again next time then the ECU make not need those more aggresive cold start settings, which will reduce the initial bark of the start-up exhaust note. It is still there, just not quite as loud.

Also, the growl exhaust intensity you get could be enhanced by other factors. Like a cold start in garage during the early morning hours when you wake the neighbors.

[HCGxKaLiBeR]

Colder the day louder it sounds : )

My 335i sounds like a V8 when engine is very cold, very quite when its hot outside.
It is all about fuel mixture and timing.

[Algeron]

I have noticed the same. My car is in sport mode, but I have the exhaust set to track mode. I have also noticed the car show touring mode on the dash then switch to sport on start up and switch back to touring when I turn it off.

[cwl011]

NPP start wide open all the time, however on cold days it will be loud. You have to remember that the colder the gas is the harder it is to atomize. This will result in a longer harder cold start.

[bhavyas]

Hmmm... My initial suspicion was the cold start... Wish the growl was louder when I start it up every single time!! Haha

[JRS]

Here's a (bad) pic of the table for startup timing. The number across the top is the engine coolant temp, the number up and down is the engine run time. The number's in the graph represent the timing taken out of the base timing as far as I know, please correct me if I'm wrong.

If you have a tuner you can adjust these settings to have that roar even when it's hot but the reason they don't do this is it make it harder for the starter to turn the engine over. It's harder to turn over because when you retard the timing the engine fires before top dead center which makes the engine kick back but when it is cold like someone said fuel doesn't atomize so you need to light it off sooner (retard timing) in order to get the engine to start and run.