Secondary air pumps whines when engine cold

[Ahsai]

I agree the bank 1 precat sensor voltage looks strange between 55s to 90s when it should have followed the green dots. Your plot and mine are very similar except for this bank 1 precat sensor reading, which did go low and merge with the green dots after 90s. Somehow it just took a lot longer to get there.

 

From the plot, we can conclude the following components are working.

- SAI pump

- SAI change-over valve

- All O2 sensors (maybe except for bank 1 precat)

- Both cats

- O2 sensors all have expected range of voltage (maybe except bank 1 precat)

 

Based on this, I think either the bank 1 precat sensor is acting up, or it's working correctly but somehow bank 1 is not getting enough air from the injection pump. To eliminate the former, You can swap the precat sensors between the two banks and relog during cold start. If the problem now shifts to bank 2, it's likely the sensor is bad. However, if it gives you the same reading on bank 1, it means the problem is bank 1 not getting enough air, which will be harder to diagnose. There is a combo SAI valve sitting close to bank 1. It's purpose is to let the air from the SAI pump to pass on to both banks and it's a one-way valve. It's difficult to explain why bank 1 is getting less air.

 

However, all of the above could have only explained P0491. Why you also get P0492? Could this be an intermittent problem that some common part for both banks doesn't work sometimes (e.g., SAI pump, change-over valve)? If you clear the codes, does it take long to reproduce both of the codes consistently? Do you always hear the SAI pump running when cold?

 

I suggest taking one more cold start log to see how consistent this peculiar bank 1 precat reading is first before you swap the O2 sensors if you're up for it. The precat sensors are quite accessible.

 

 

I really want to try and fix this problem now.  I started the car, and recorded until the RPM dropped & the SAI shut off.  I'm looking for opinions on what you see.  To me, the O2 voltage ahead of cat bank 1 looks funky.  Anyone agree or disagree?  What should my next action be?  Thanks!

Edited May 26, 2015 by Ahsai

[DK570]

I did another log tonight, and it looks more like how I would expect it to.  That first one may have been a fluke.  

 

When I clear the codes they usually come back in less than a week.  (if the ambient temperature is warm enough).  I've never not noticed the SAI pump running when cold.  I cleared the codes yesterday, and drive about 50mi every day.   We'll see how long until they come back & I'll try to pay attention to if the pump is running or not when cold.   

 

 

Copy of 2015_05_26_21_17_28.pdf

[Ahsai]

Yea, this one looks great. Seems to me the cold start is fine. Do you drive on highways a lot and the SAI pump will run after exiting the highway?

[Ahsai]

Btw, do you use an Android or iphone? You can get a wireless OBDII adaptor that can read and plot the four O2 sensors when you are driving. I have a smartphone holder attached to my windshield for this purpose.

[DK570]

Yea, this one looks great. Seems to me the cold start is fine. Do you drive on highways a lot and the SAI pump will run after exiting the highway?

Yes, I notice it a lot on my way to work.  I'll drive 20mi on the highway, than more often than not I'll get a red light at the end of my exit ramp and I'll hear it come on.  Sometimes accompanied by a few seconds of a slightly lump idle.    Driving home I usually get a few blocks of 30-40 mph after the highway before I hit a red light.  I notice it less in this situation, compared to 20mi of 80mph immediately followed by a minute of 0 mph.   

[DK570]

Btw, do you use an Android or iphone? You can get a wireless OBDII adaptor that can read and plot the four O2 sensors when you are driving. I have a smartphone holder attached to my windshield for this purpose.

I have an iphone.  Maybe I'll look into the wireless adapter.  I think my next step is to replace some components, as I'm thinking I have a vacuum leak.  I've looked at your thread here:http://rennlist.com/forums/996-forum/849770-mkii-996-vacuum-line-routing-and-related-components.html which is quite helpful.  My check valve does of some oil mist on it, so maybe it's gone bad, but that could be a coincidence.  I'm having a bit of trouble finding some of the components in the Porsche catalog though.  I've found this diagram which shows some of it: http://sonnenporscheoemparts.com/parts/2002/Porsche/911/Carrera%204/?siteid=215405&vehicleid=44889&section=EMISSION%20SYSTEM But I can't find a diagram that shows the parts closer to the throttle body. 

[Ahsai]

Best parts diagrams are on autoatlanta.com You should find all the parts you need here

http://www.autoatlanta.com/porsche-parts/996-99-05/porsche_911_parts.php

 

Yes, I think it's wise to just replace all the vacuum components including the vacuum reservoir since the parts are relatively cheap and they are prone to leak anyway. You can eliminate a lot and has a good chance to fix the problem too.

[Ahsai]

For iOS, the OBDII fusion app is great for daignostic purposes. Hopefully you could catch the problem in action e.g., if you hear the pump running but yet the O2 readings don't drop, you know the exhaust is not getting the injected air, which points to a vacuum/valve problem.

[DK570]

 

 

In my recently bought 2004 C4S, I am getting a high pitched whining from the engine bay (when hot), that changes frequency with engine revs. Any ideas what this could be?

If it changes with revs, I doubt it's the SAI pump. 

 

However, while we are on the subject of SAI, I have codes p0491, and p0492 that reoccur.  These are secondary air injection bank 1 and bank 2.  I'm thinking about replacing every hose + the reservoir.  Looks like you can access all of that if you remove the intake plenums?  Any other ideas?  

 

It's strange in that I only get the codes when it's above freezing.  I've been able to clear the codes, and not have them come back until the temp reaches about 34º on a few different occasions, so I don't think it's a coincidence.   

 

 

 

You only need to remove the alternator and the rear (rear of the car) intake plenum.

 

Are you sure you only need to remove the alternator and rear plenum?  I've gotten that far, but aren't sure what to do now.  

[SpawnyWhippet]

Turns out I had 2 problems - noisy water pump and noisy SAI, producing almost exactly the same kind of whining noise. I rebuilt and greased the SAI bearings and replaced the water pump and all is well now.

 

 

In my recently bought 2004 C4S, I am getting a high pitched whining from the engine bay (when hot), that changes frequency with engine revs. Any ideas what this could be?

If it changes with revs, I doubt it's the SAI pump. 

 

However, while we are on the subject of SAI, I have codes p0491, and p0492 that reoccur.  These are secondary air injection bank 1 and bank 2.  I'm thinking about replacing every hose + the reservoir.  Looks like you can access all of that if you remove the intake plenums?  Any other ideas?  

 

It's strange in that I only get the codes when it's above freezing.  I've been able to clear the codes, and not have them come back until the temp reaches about 34º on a few different occasions, so I don't think it's a coincidence.   

 

[Ahsai]

DK570, it's tight and you have to work around the SAI combo valve and the wires. Maybe undo the starter cables to get more space. The vacuum reservoir is only held down by a single metal screw.

[DK570]

After I took the starter out I was able to find enough room.  

[DK570]

Good news, it's been 3 days since I replaced everything, and no CEL.  It seems to start quicker, and hold a more steady idle.  Even better, I passed emissions today!  Thanks for the help Ahsai!

[Ahsai]

Happy to hear that!

[Ahsai]

BTW, what parts did you end up replacing?

[DK570]

I replaced everything seen in your pic:

Except not the plenum or resonance flap actuator.  Also, the dealer only gave me 1m of line, not 2m, so the 122mm bit is still original, but that's the easiest one to replace later.  Also, I mis-counted the number of elbows needed, so the elbow to the one way check is original.  Again easy to replace later.  For anyone doing this in the future, you need 5 elbows, not 4.  While I was in there, I replaced the starter.  I also replaced a couple hose/line holders that I had broken previously when replacing the alternator last year (maybe 2 years ago). 

[Ahsai]

Hey, that pic looks familiar :)

 

Now you got me curious, I counted 4 elbows in the pic. Where' the 5th?

 

Good that you finally fixed the annoying CEL and hopefully it stays OFF.

[DK570]

The angle looking at changeover valve #2 is just right so you can't really see one of the elbows.  Circled in Blue below:

 

It's a little confusing ordering the parts since the diagram that Porsche uses shows the old style shut off valve from 1999 which has a bit different plumbing. 

[Ahsai]

Oh now I remember. The circled part is a straight tube (99923904040) I think, different than the other 4 90 degrees elbows (92857471705).

Edited July 22, 2015 by Ahsai

[dedens]

On 7/22/2015 at 10:40 AM, DK570 said:

I replaced everything seen in your pic:

Except not the plenum or resonance flap actuator.  Also, the dealer only gave me 1m of line, not 2m, so the 122mm bit is still original, but that's the easiest one to replace later.  Also, I mis-counted the number of elbows needed, so the elbow to the one way check is original.  Again easy to replace later.  For anyone doing this in the future, you need 5 elbows, not 4.  While I was in there, I replaced the starter.  I also replaced a couple hose/line holders that I had broken previously when replacing the alternator last year (maybe 2 years ago). 

I am in the process of replacing my Air/Oil Separator and snapped/broke the hose/line that you have marked 428mm.  For the life of me I cannot find the part number.  Can you point me in the right direction?

[DK570]

12 hours ago, dedens said:

I am in the process of replacing my Air/Oil Separator and snapped/broke the hose/line that you have marked 428mm.  For the life of me I cannot find the part number.  Can you point me in the right direction?

I think it's 4320501

[rcs21080]

Since yesterday I heard a high pitch whining sound, it was the secondary air pump. This morning I have taken the pump apart, is actually quite easy, and replaced the two bearings of the e-motor. Bearings are standard, number 608s, bought for $20 at a local car parts shop. All works fine again.

2 hour job, that's all, saved myself a lot of money. So it can be done...

[todd1230]

Let me just say that i have a 99 911 same thing on cold start

Its a German thing my CLK55 does the same **** thing

 

Lets make an aftermarket one and get rich! ANYONE? I'm serious!

[ziiz996]

Bumping this old thread...  Had the same whine.  Ignored it for years.  Lately it started whining AND smelling like STRONG burnt rubber..  This behavior is kinda similar to my ex's.  Lol.   Guess no longer an option to ignore.  Previous feedback should make it much easier..  

 

@@Loren.

Good to know that you're still our Shepard on this site.   Thank you for the thousands of collaborations over the years.

BTW, Who said 996s are not reliable.  Had it for 21 years (Knock on wood). Tok Tok..  Still puts a huge smile on my face when those RPMs hit 6900 in the twisties.   Am also driving now a much newer insanely fast n smooth DSG 500HP S4..  A lot of fun,  but..............There's something about that 911.

 

Cheers my friend for life.  

Edited July 24, 2021 by ziiz996
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