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This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 07-26-2010, 05:46 PM   #1
Adam330i
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What does the secondary air pump do?

A few months back I replaced the hose that connected between the pump and the valve because it was ripped open. I am now wondering what the use of the air pump and the valve are. I know the have to do with the emissions system, and am curious if it has anything to do with my P0444 code Emission control Purge valve circuit open. I am about to purchase the Fuel Tank Breather valve a.k.a Purge valve, hoping this will fix the issue.
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Old 07-26-2010, 07:14 PM   #2
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Hmmm...wondering if maybe you just got gunk clogging up the inlet for the valve like I did.

Try removing the hose you replaced from the valve and looking in the inlet. If your hose had a hole like mine, from corroded crap from the inside of hose, then maybe your valve is just plugged.

That, or maybe you've sprung a leak on the tiny hose leaving the valve...I had a small crack on mine...a little dab of rtv has held that fine for months now.

HTH

Oh, from what I understand, the SAP is part of the emissions but other than blow air into somewhere, you've got me what it does or why.

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Old 07-26-2010, 07:15 PM   #3
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basically dilutes the exhaust on start up, for emissions purposes..
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Old 07-26-2010, 11:46 PM   #4
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Quote:
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basically dilutes the exhaust on start up, for emissions purposes..
Where do you people get your info? It doesn't dilute the exhaust.

It pumps cold air into the the catalytic converters in order to bring them up to operating temperature quicker.
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Old 07-26-2010, 11:49 PM   #5
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Quote:
Originally Posted by dakkon View Post
basically dilutes the exhaust on start up, for emissions purposes..
right

Quote:
Originally Posted by Arsevader View Post
Where do you people get your info? It doesn't dilute the exhaust.

It pumps cold air into the the catalytic converters in order to bring them up to operating temperature quicker.
what? how would pumping cold air bring something up to temperature!lol


It pumps clean air into the cats to dilute the leftover air for emisions purposes before it leaves the exhaust..


My moms e46 recently had a problem with the SAP and was fixed by replacing the hose and doing the seafoam treatment in the same hose leading from the pump to the valve, there is a nice DIY somewhere on the forums.
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Last edited by Stanc3; 07-26-2010 at 11:53 PM.
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Old 07-27-2010, 12:12 AM   #6
dakkon
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Where do you people get your info? It doesn't dilute the exhaust.

It pumps cold air into the the catalytic converters in order to bring them up to operating temperature quicker.
wiki source..
http://en.wikipedia.org/wiki/Secondary_air_injection
then there is this
http://www.obd-codes.com/p0410
and then there is this
http://repairpal.com/secondary-air-system

this last article leads me to think your reading comprehension is not that great?

But i could be wrong about your reading comprehension, so could you please explain the physics of your statement to me?

how does pumping ambient temperature air, help the catalytic converters heat up, aren't the catalytic converters already at ambient temperature?

I would think the exhaust from the combustion chambers at several hundred degrees would do a much better job at heating up the exhaust system?


so i guess my question for you is, where do you get your information from?
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Old 07-27-2010, 12:17 AM   #7
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super lol @ alex fight idiots.

on a seperate note, it really helps to pull the whole assembly when trying to reach the top nuts on aftermarket headers.
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Old 07-27-2010, 12:24 AM   #8
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wiki source..
http://en.wikipedia.org/wiki/Secondary_air_injection
then there is this

this last article leads me to think your reading comprehension is not that great?

But i could be wrong about your reading comprehension, so could you please explain the physics of your statement to me?

how does pumping ambient temperature air, help the catalytic converters heat up, aren't the catalytic converters already at ambient temperature?

I would think the exhaust from the combustion chambers at several hundred degrees would do a much better job at heating up the exhaust system?


so i guess my question for you is, where do you get your information from?
Maybe you should read your own links before playing on the internet...simple physics.

First link provided by you.

"When the engine is cold, air injected at this point cleans up the extra-rich exhaust and raises the temperature of the exhaust so as to bring the catalytic converter to operating temperature quickly. Once the engine is warm, air is injected to the downstream location - the catalytic converter itself - to assist with catalysis of unburned hydrocarbons and carbon monoxide."

I could provide a dozen or so articles on this concept but this should suffice. I think your misunderstanding of the subject comes from the fact that most articles just state that the system injects air to 'lower emissions' without explaining how this actually occurs. It is not because the exhaust gases are somehow diluted, it is because the extra oxygen heats up the cats quicker therefore letting them do their job faster.
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Last edited by Arsevader; 07-27-2010 at 12:27 AM.
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Old 07-27-2010, 12:49 AM   #9
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so where is a link, and or explanation as to how ambient temperature air, can "heat" up exhaust gases, maybe a chemical reaction in the cat?

and no wiki, is not the best source of documentation since anyone can edit it........

hence the reason i provided 2 others...

so, if you would be so kind as to explain, and or link where i can read how the secondary air pump warms up the cats.
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Old 07-27-2010, 12:56 AM   #10
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Originally Posted by Arsevader View Post
Maybe you should read your own links before playing on the internet...simple physics.

First link provided by you.

"When the engine is cold, air injected at this point cleans up the extra-rich exhaust and raises the temperature of the exhaust so as to bring the catalytic converter to operating temperature quickly. Once the engine is warm, air is injected to the downstream location - the catalytic converter itself - to assist with catalysis of unburned hydrocarbons and carbon monoxide."

I could provide a dozen or so articles on this concept but this should suffice. I think your misunderstanding of the subject comes from the fact that most articles just state that the system injects air to 'lower emissions' without explaining how this actually occurs. It is not because the exhaust gases are somehow diluted, it is because the extra oxygen heats up the cats quicker therefore letting them do their job faster.
Finaly someone who knows his stuff.

Another thing the pump do is to give the post-o2 sensors a lean condition , to test that they're working
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Old 07-27-2010, 01:11 AM   #11
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It's interesting that BMW had improved the design of the secondary air injection system while the E46 was in production. The early models (such as my car) have a simple air pump that just blows air at constant rate into the exhaust manifold for about 90 sec on cold starts. This huge excess of oxygen helps to burn the incompletely spend fuel exiting the cold engine even when the catalytic convertors aren't warm yet. Of course, this also produces additional heat that quickly brings the cats to operating temp.
However, too much excess of oxygen can't be good for the pipes, etc. The late E46 models are equiped with a secondary MAF, which monitors how much air is being pump into the exhaust. This allows the secondary air pump output to be controlled, avoiding too lean exhaust conditions.

Last edited by Megalocnus; 07-28-2010 at 12:39 AM.
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Old 07-27-2010, 01:24 AM   #12
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This huge excess of oxygen helps to burn the incompletely spend fuel exiting the cold engine even when the catalytic convertors aren't warm yet.

http://www.google.com/url?sa=t&sourc...Q7q5_HZkki1X1g

This is the only credible source i was able to find, as they are a manufacture of secondary air pumps......

This explains the purpose of the added oxygen.
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Old 07-27-2010, 06:30 AM   #13
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Glad you realize your mistake. Don't get so hung up on the temperature of ambient air or that this is heating up exhaust gases somehow. The heat comes from the reaction of the extra oxygen not the temperature of the air. If emission control was as easy as diluting the exhaust gases as it leaves the engine then no car would have cats. This is why most if not all smog tests will test for dilution to catch 'cheating' of clean air mixing with exhaust gases before it leaves the tailpipe.

From your link.

"The reason being that during this period the catalytic converter is not fully operable. Here is where secondary air brings its benefits. Injecting sec- ondary air into the exhaust manifold initiates an exothermal oxidation of the unburnt hydrocarbons (HC). Consequently, HC and CO emissions are reduced during cold start while at the same time the light-off time of the catalytic converter is shortened."

http://www.ge39.com/files/m54x5.pdf

Page 37 of this PDF explains it as well.


Quote:
Originally Posted by dakkon View Post
This is the only credible source i was able to find, as they are a manufacture of secondary air pumps......

This explains the purpose of the added oxygen.
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Old 12-03-2013, 09:26 AM   #14
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I have a question,, will a leak in this system cause an idle issue? my e46 will start and stall. but if you keep your foot on the gas it will run. as soon as i let off it stalls. trying to figure out my idle issue..help
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Old 12-03-2013, 09:33 AM   #15
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What does the secondary air pump do?

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Originally Posted by Timmi0304 View Post
I have a question,, will a leak in this system cause an idle issue? my e46 will start and stall. but if you keep your foot on the gas it will run. as soon as i let off it stalls. trying to figure out my idle issue..help
No, as the leak is in the exhaust side of the engine. It sounds like you have a vacuum leak.


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Old 12-03-2013, 09:33 AM   #16
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What does the secondary air pump do?

Any CEL light? Have the ECU read for codes.


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Old 12-03-2013, 09:43 AM   #17
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Don't have emissions here in AL so I did an EU2 flash and took all that crap off anyways. Less to worry about. If WI doesn't do emissions either then consider that.

Edit: Annd just realized this is a zombie thread!

Still goes though. If your having problems with the emissions on your vehicle be it sap or cats and live in a state where they don't do emissions then consider an eu2 flash and delete the sap and cats..

Last edited by Encryption76; 12-03-2013 at 09:51 AM.
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Old 12-03-2013, 11:23 AM   #18
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I have a question,, will a leak in this system cause an idle issue? my e46 will start and stall. but if you keep your foot on the gas it will run. as soon as i let off it stalls. trying to figure out my idle issue..help
I know you are new here, you should check the dates on posts before you add to them!

You need to do 2 things.

1st spend some money, as little as $25 and buy yourself and OBDII scan tool, you WILL need it. Read this - http://forum.e46fanatics.com/showthread.php?t=967204

Then read the 1st link below in my signature. Plenty of vacuum leaks under the hood that can cause problems. Start with replacing the lower intake boot, DISA O-ring and the CCV lower oil return line. Both intake boots probably need replacement along with the entire CCV, but you may be able to buy some time with just the few basics.
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