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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 06-06-2004, 10:13 PM
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Question Humming noise at start up, anyone else get it?

On my 02 I notice that there is a deep humming noise upon start up that will last a minute or two. I thought it was especially evident when the engine is cold, but now that I reflect on it I'm thinking it comes up regardless.

Its not me or the passenger humming, so does anyone have an idea what this sound is, if its normal or something to look into?
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  #2  
Old 06-06-2004, 10:59 PM
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Ron Stygar Ron Stygar is offline
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Quote:
Originally Posted by eVal
On my 02 I notice that there is a deep humming noise upon start up that will last a minute or two. I thought it was especially evident when the engine is cold, but now that I reflect on it I'm thinking it comes up regardless.

Its not me or the passenger humming, so does anyone have an idea what this sound is, if its normal or something to look into?
Secondary air pump? Back of the engine compartment on the passenger side. Runs on cold start for up to 90 seconds.
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  #3  
Old 06-06-2004, 11:01 PM
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Quote:
Originally Posted by eVal
On my 02 I notice that there is a deep humming noise upon start up that will last a minute or two. I thought it was especially evident when the engine is cold, but now that I reflect on it I'm thinking it comes up regardless.

Its not me or the passenger humming, so does anyone have an idea what this sound is, if its normal or something to look into?
Also check your power steering fluid level. It might be a bit low causing the pump to cavitate a bit but once it expands on heating it goes away. Admittedly a wild ass guess.
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  #4  
Old 06-07-2004, 08:45 AM
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Guess not everyone has it then? Well, the car seems fine so I guess its not urgent, will ask the dealer next time it goes in I suppose (and I might as well check the power steering)

Thanks for trying to help
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  #5  
Old 06-07-2004, 11:25 AM
Ben Carufel Ben Carufel is offline
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Val, I'm almost positive it's the SAP like Ron said...I had the same question after I owned my Coupe for a few months and finally noticed it...

It sounds like it's coming from right behind the glove compartment, which is where the SAP is (inside the engine bay in that little gasket-lined corner).
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  #6  
Old 06-07-2004, 11:49 AM
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Mine makes the sound too. SAP sound from glovebox area = "they all do that".
(another description would be it sounds like a big PC cooling fan )
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  #7  
Old 06-07-2004, 11:53 AM
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All E46s make this noise (and presumably any other car that uses M52/M54/S52/S54 engines) on cold start, and it's the SAP. You can feel it vibrating if you put your hand on it while it makes the noise.
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  #8  
Old 06-07-2004, 12:21 PM
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Every 96 and newer bimmer I6's I've worked on has done it as well. SAP without doubt.
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  #9  
Old 06-07-2004, 01:48 PM
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Thanks for the replies, it makes me feel better to know that its likely a normal thing.

By the by, it is a fairly loud sound, and I do not have the same thing on my 2000 328Ci.
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  #10  
Old 06-07-2004, 01:56 PM
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Quote:
Originally Posted by eVal
Thanks for the replies, it makes me feel better to know that its likely a normal thing.

By the by, it is a fairly loud sound, and I do not have the same thing on my 2000 328Ci.
Next cold start, open the hood and look in the compartment on the passenger side by the windshield. Put your hand on the pump and see if the noise goes away after 90 seconds.
There is also a fan in the DME enclosure which is located in the same compartment.
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  #11  
Old 06-07-2004, 05:04 PM
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Just out of curiosity, what does the secondary air pump do?
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  #12  
Old 06-07-2004, 07:00 PM
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Quote:
Originally Posted by avalys
Just out of curiosity, what does the secondary air pump do?
Connect to:
http://www.unofficialbmw.com/images/...20Part%203.pdf

and check out page 68.

Last edited by Ron Stygar; 06-07-2004 at 07:53 PM.
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  #13  
Old 06-07-2004, 07:46 PM
Ben Carufel Ben Carufel is offline
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Quote:
Originally Posted by Ron Stygar
Must be the wrong attachment, Ron -- that one only goes to 59.
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  #14  
Old 06-07-2004, 07:53 PM
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Quote:
Originally Posted by Ben Carufel
Must be the wrong attachment, Ron -- that one only goes to 59.
Should work now.
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  #15  
Old 10-18-2013, 05:09 AM
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Resurrecting an old thread just to avoid starting a new one. I found this thread via Search.

Cooler weather has arrived and my Z3 has begun emitting an occasional un-characteristically loud screech. The belts are new, as are the pulleys, etc.

Reading a bit I think the SAP is getting ready to croak.

And (drum roll here) ... the parts to completely replace it are in excess of $400.

Any suggestions on a DIY short-term fix, or otherwise inexpensive repair?
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  #16  
Old 10-18-2013, 08:28 AM
Blacklane Blacklane is offline
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I'm not sure I would replace the SAP on a hunch. It should be easy to sort-out SAP noises from belts and other noises by standing outside the car with the hood up at start-up.
You should also know that the SAP often fails as a result of the SAP valve failing first, allowing hot exhaust gas to blow into the pump. I would replace the valve and hose along with the pump.
After considering everything, I replaced my SAP with a "SAP Simulator" which simply applies the correct voltage to the oxygen sensor circuit for a minute or two at start-up fooling the DME into passing the SAP test so it doesn't set the Service Engine Light. (The SAP test involves reading the O2 sensor voltages, turning on the SAP, and re-reading the voltages. If the upstream O2 sensor voltage decreases, SAP must be working).
There was plenty of room to install the simulator box inside the DME box. My SAP is still in-place. I also installed a steel plate between the SAP valve and the exhaust manifold to prevent blow-by.
While I agree this is not the best answer for everyone, I considered the complexity, cost, and reliability of this system against the benefit of about 90 seconds of additional air for the catalyst when cold, and it just didn't make sense to me. There are billions of cars on the road without this system, and I'm not sure why BMW felt this approach was necessary.

Last edited by Blacklane; 10-18-2013 at 08:35 AM.
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  #17  
Old 10-18-2013, 09:17 AM
wordsmyth wordsmyth is offline
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Quote:
Originally Posted by Blacklane View Post
I'm not sure I would replace the SAP on a hunch. It should be easy to sort-out SAP noises from belts and other noises by standing outside the car with the hood up at start-up.

You should also know that the SAP often fails as a result of the SAP valve failing first, allowing hot exhaust gas to blow into the pump. I would replace the valve and hose along with the pump.

After considering everything, I replaced my SAP with a "SAP Simulator" which simply applies the correct voltage to the oxygen sensor circuit for a minute or two at start-up fooling the DME into passing the SAP test so it doesn't set the Service Engine Light. (The SAP test involves reading the O2 sensor voltages, turning on the SAP, and re-reading the voltages. If the upstream O2 sensor voltage decreases, SAP must be working).

There was plenty of room to install the simulator box inside the DME box. My SAP is still in-place. I also installed a steel plate between the SAP valve and the exhaust manifold to prevent blow-by.

While I agree this is not the best answer for everyone, I considered the complexity, cost, and reliability of this system against the benefit of about 90 seconds of additional air for the catalyst when cold, and it just didn't make sense to me. There are billions of cars on the road without this system, and I'm not sure why BMW felt this approach was necessary.
Thanks for the feedback! Also, when I did the quote your post showed paragraphs that the original did not have so I added the spaces.

So --

Can you direct me to a source for this SAP Simulator?

My typical warm up ritual involves starting the car (or my truck, or any vehicle) and then getting my various stuff in order, be it mileage entries, coffee cup, cell phone and headset, etc. Then I ease of out of my residential neighborhood at a modest creep lest I have an encounter with a walker, a kid, or perhaps even a dog.

Usually by the time I do all that and get to the highway the engine is warm enough for driving. So I'm very interested in this SAP simulator option.

Thanks again.
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  #18  
Old 10-18-2013, 01:50 PM
Blacklane Blacklane is offline
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Just Google "BMW SAP Simulator". There are many sources including Amazon.
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