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Evening all,

Just signed up after recently acquiring a 2011 RS5. Hoping to find lots of knowledge, experience & insights on various topics.

First thing that's surprised me about this car is the Cold Start sequence, which I believe AUDi have programmed in on purpose to make it an "event" for owners each time.

Lots of rattles & noise, plus open exhaust valves - is this just pure theatre or is there a specific purpose.

Have read the increase rpm is to get oil pressure up quickly, reducing the chain & lifter noise, plus the open exhaust valves to help mask the noise ?

Have also read a mis-fire is programmed in to create a crackle (again, to mask the rattly engine ??)

First time I heard the car start from cold, i thought it was worn out already !

Double FON
Pictures required

Hi Sparklyman welcome to the forum. The RS5 section is a little quiet on here, so it might be worth also dipping into the B8 RS4 section as well, due to them being the same platform and sharing a lot of componentry.

To answer your question, the cold start up sequence is louder due to a secondary air injection system. This system pumps additional air into the exhaust stream at the cylinder head to dilute the unburned hydrocarbons created from the cold (inefficient) engine. The now better mixed exhaust gasses can then be catalysed more efficiently by the catalytic convertor in this cold engine state. Once the engine starts warming up, the inefficiency improves to a level where the secondary air injection system is no longer necessary and it stops, the engine idle reduces and the car becomes quieter.

The exhaust valves should shut close within the start of this sequence; so maybe worth checking that happens, to ensure there is no vacuum leak.

Hey Sam - thanks for the reply and explanation of what's happening during a cold start - appreciate the knowledge share, just what I was hoping to find here.

Rear Silencer Valves are working fine, but I think I hear other exhaust valving at work during the cold start, seems to be around the transmission area....or is this the air injection shutting down, with a corresponding reduction in exhaust noise ? The ramp down in loudness starts to occur just before the revs tail off to idle.

The car always starts with Drive Select in Auto - if I switch to Dynamic during the cold start, the back end gets louder, so I assume the cold start sequence has rear silencer valves closed by default ?

Now you've explained what's happening, I'll be listening more closely at tomorrows start....

sparklyman wrote: ↑

Mon Aug 06, 2018 9:58 pm

Rear Silencer Valves are working fine, but I think I hear other exhaust valving at work during the cold start, seems to be around the transmission area....or is this the air injection shutting down, with a corresponding reduction in exhaust noise ? The ramp down in loudness starts to occur just before the revs tail off to idle.

Yes, that'll be secondary air injection system you are hearing

sparklyman wrote: ↑

Mon Aug 06, 2018 9:58 pm

The car always starts with Drive Select in Auto - if I switch to Dynamic during the cold start, the back end gets louder, so I assume the cold start sequence has rear silencer valves closed by default ?

Now you've explained what's happening, I'll be listening more closely at tomorrows start....

Sound like you have vacuum and all is normal with the valves, if it gets louder when switching to dynamic.

Hi Sparklyman - I too have just purchased an RS5 and so far so good. How is your ownership going? Any tips/concerns you want to share?

Nick

ps - where in Surrey are you? I'm down in Winchester.

Hi, I have a 2015 rs5 v8 for 3 weeks now , grrrreat.
I have noticed that on cold start it cranks probably 1 -2 times then fires up with high revs...is this normal?
someone told me it should crank 5 - 6 times then fire up to help oil get around pre firing up.
Someone also also mentioned this is controlled by some sort of cold start valve or "valencer", I didn't quite get his pronunciation

Any info guys......?