What makes the car loud on cold start?
What makes the car loud on cold start?
When you start the car, it runs noisily for the first 1-2 minutes. The idle rpm is slightly higher (as expected) but its more noisy than when warm at the same rpm. Its also louder while driving and you can hear it quieten down, it's like something is turning off. I was wondering what is it doing to make it that much louder?
Sorry for the dumb question.
Thanks,
Sorry for the dumb question.
Thanks,
Re: What makes the car loud on cold start?
The secondary air injection kicks in to keep emissions down by warming up the catalytic converter quickly.
Re: What makes the car loud on cold start?
Quote from a webpage:
With spark-ignition engines, the greatest pollution occurs on cold starting. Secondary-air systems have been successfully employed to reduce such cold starting emissions.
A “rich mixture” (λ<1), i.e. a mixture with excess fuel, is required for starting a cold spark-ignition engine.
Until the catalytic converter reaches operating temperature and Lambda control action starts to take effect, large quantities of carbon monoxide and unburnt hydrocarbons are produced.
To reduce the level of these pollutants, ambient air with a high oxygen content (“secondary-air”) is injected into the exhaust manifold directly downstream of the exhaust valves during the cold starting phase. This results in post-oxidation (“afterburning”) of the pollutants to form carbon dioxide and water.
The heat generated in this process additionally warms the catalytic converter and speeds up the onset of Lambda control action.
With spark-ignition engines, the greatest pollution occurs on cold starting. Secondary-air systems have been successfully employed to reduce such cold starting emissions.
A “rich mixture” (λ<1), i.e. a mixture with excess fuel, is required for starting a cold spark-ignition engine.
Until the catalytic converter reaches operating temperature and Lambda control action starts to take effect, large quantities of carbon monoxide and unburnt hydrocarbons are produced.
To reduce the level of these pollutants, ambient air with a high oxygen content (“secondary-air”) is injected into the exhaust manifold directly downstream of the exhaust valves during the cold starting phase. This results in post-oxidation (“afterburning”) of the pollutants to form carbon dioxide and water.
The heat generated in this process additionally warms the catalytic converter and speeds up the onset of Lambda control action.
Re: What makes the car loud on cold start?
Ive removed all of my secondary air system, I am yet to start the car as still putting it all back together will it still be louder because of the additional fuel?
2007 B7 RS4 Saloon, Phantom Black, Forge Oil Cooler Kit, custom home made air feed, H&R Coilovers, H&R anti roll bars, 10mm H&R Spacers, Milltek decat downpipes, Milltek Non Res Valved Exhaust, Reyland Motorsports front & rear discs with Hel braided Hoses, full underbody overhauled inc powdercoated subframes and arms, 034 solid subframe bushes and every joint, arm or bush replaced.
Re: What makes the car loud on cold start?
Just a guess but I think it will still be loud as there is different fuelling and timing (maybe?) involved too. MRC normally map out the cold start when doing remaps as most customers also have noisier exhausts so it makes them a little more neighbour friendly.
Re: What makes the car loud on cold start?
Probably still loud but running rich until I can get it mappedMikeFish wrote: ↑Fri Jun 07, 2019 2:43 pmJust a guess but I think it will still be loud as there is different fuelling and timing (maybe?) involved too. MRC normally map out the cold start when doing remaps as most customers also have noisier exhausts so it makes them a little more neighbour friendly.
2007 B7 RS4 Saloon, Phantom Black, Forge Oil Cooler Kit, custom home made air feed, H&R Coilovers, H&R anti roll bars, 10mm H&R Spacers, Milltek decat downpipes, Milltek Non Res Valved Exhaust, Reyland Motorsports front & rear discs with Hel braided Hoses, full underbody overhauled inc powdercoated subframes and arms, 034 solid subframe bushes and every joint, arm or bush replaced.
Re: What makes the car loud on cold start?
MikeFish wrote: ↑Fri Jun 07, 2019 12:04 pmQuote from a webpage:
With spark-ignition engines, the greatest pollution occurs on cold starting. Secondary-air systems have been successfully employed to reduce such cold starting emissions.
A “rich mixture” (λ<1), i.e. a mixture with excess fuel, is required for starting a cold spark-ignition engine.
Until the catalytic converter reaches operating temperature and Lambda control action starts to take effect, large quantities of carbon monoxide and unburnt hydrocarbons are produced.
To reduce the level of these pollutants, ambient air with a high oxygen content (“secondary-air”) is injected into the exhaust manifold directly downstream of the exhaust valves during the cold starting phase. This results in post-oxidation (“afterburning”) of the pollutants to form carbon dioxide and water.
The heat generated in this process additionally warms the catalytic converter and speeds up the onset of Lambda control action.
Thanks Mike
Re: What makes the car loud on cold start?
Does that map stop the secondary air injection? I had seen it on their website, but just assumed it stopped the little rev of the engine on start-up.
Re: What makes the car loud on cold start?
Yes it still will be loud. Mine is.James1984 wrote:Ive removed all of my secondary air system, I am yet to start the car as still putting it all back together will it still be louder because of the additional fuel?
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RS4 B7 aka Vinnie
AMD stage2|De-coked|GruppeM|CAF|Eibach arbs|BilsteinB14|Goodridge hoses|DS3000|phaeton brake ducts|Led tail lights|Trups DTRL|LED interior|JcWeldFab|034 motorsport endlinks, mounts and bushings|ECS Differential Mount|JHM short shift|JHM intake spacers|8/10mm H&R|R2D2 10" sub and AMP|Corbeau seats|4point harness
RS4 B7 aka Vinnie
AMD stage2|De-coked|GruppeM|CAF|Eibach arbs|BilsteinB14|Goodridge hoses|DS3000|phaeton brake ducts|Led tail lights|Trups DTRL|LED interior|JcWeldFab|034 motorsport endlinks, mounts and bushings|ECS Differential Mount|JHM short shift|JHM intake spacers|8/10mm H&R|R2D2 10" sub and AMP|Corbeau seats|4point harness
Re: What makes the car loud on cold start?
Thanks! I think I will get mine mapped out, although I don’t mind it my car will be garages soon and not sure the neighbours would appreciate it bouncing off the walls.
2007 B7 RS4 Saloon, Phantom Black, Forge Oil Cooler Kit, custom home made air feed, H&R Coilovers, H&R anti roll bars, 10mm H&R Spacers, Milltek decat downpipes, Milltek Non Res Valved Exhaust, Reyland Motorsports front & rear discs with Hel braided Hoses, full underbody overhauled inc powdercoated subframes and arms, 034 solid subframe bushes and every joint, arm or bush replaced.
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