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Heck, I’m only 5 not 71!
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Odd Auxiliary Air Valve installed
I do know that the Auxiliary Air Valve (AAV) is open when the engine is started and as soon as ~8" of vacuum is created it closes. I also know that to purchase an OEM replacement part you are looking at ~$1000. So I can understand that my 1980 SC has a different Auxiliary Air Valve (AAV) installed than what is required probably due to the cost. Prior to my air box being blown I did not have any issues with starting the car and warmup from a cold engine worked as advertised. The only issue I noticed was a slightly higher idle speed of ~1000 to 1100 rpm after deceleration. A blip on the gas pedal would drop it down to 900 rpm.
The Porsche parts manual calls out the following: Porsche OEM part # 911 110 273 01 superseded by 911 110 273 AX Also the Bosch part # 0280160405 has been used. This AAV has a small air hole on the side of the unit opposite the hose connection side for air equalization.  What is installed in my car for the AAV is Bosch part # 0280160404 and it has the vacuum nipple like the Deceleration valve in bottom of the below picture. The nipple would perform the same function as the air hole in the correct part. I will need to see if this valve is normally open and will close with the ~8" of vacuum. Does anyone have a tech comparison between the two Bosch part numbered parts? 
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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12-11-2020, 07:51 PM
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AAVs are available on ebay. When the original on my 1978SC started cutting out too soon I found one for about £125 ($150) which gave a longer period before it closed and solved the problem of the engine's tendency to stall while warming up. I have since bought yet another spare for a similar price as it seemed it bit of a bargain.
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1959 Bristol 406 (bought in 1972; sold in 1977) 1966 Porsche 2.0 coupe (bought in 1977; sold 1981) 1978 Porsche SC coupe (bought in 1993) |
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12-12-2020, 03:02 AM
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Heck, I’m only 5 not 71!
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Quote:
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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12-12-2020, 04:37 AM
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I believe that's a decell valve. I took all that crap off and tossed it in the garbage.
This is a auxiliary air valve: |
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12-12-2020, 05:45 AM
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Heck, I’m only 5 not 71!
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From my research the part number 0280160404 that is in my car is an Auxiliary Air Valve (AAV). Granted, it may be off of another model CIS system i.e. Volvo, Mercedes, BMW and that is what I am trying to decipher. I have previously maintained my lambda CIS system with minimal issues. For the most of my ownership of this car it has performed very well even with an odd AAV installed. Because I had a recent backfire that damaged the air box I have had the pleasure of removing the CIS system. So, I am in the process of inspecting all the parts and have come across this issue.
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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12-12-2020, 06:22 AM
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CIS components........
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You have the wrong part. That is not a AAV. It is a DV (decel valve) used in late SC models. If you need one, I would be more than happy to send one to you. Tested and guaranteed to work.  PM me your shipping address. And I would appreciate if you could give something in return to my wife. Who calls these stuff as JUNK. Maybe a jar of jam or jelly or something else not expensive. So I could keep my junk in the garage and make her happy.  Assorted Bosch decel valves used in CIS. They are normally closed and open up when vacuum valve is activated. Tony Last edited by boyt911sc; 12-12-2020 at 07:29 AM.. |
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12-12-2020, 06:33 AM
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Heck, I’m only 5 not 71!
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We can both agree that the Deceleration valve in the 1980 SC is one of three alternate air sources that bypass the the throttle plate to supply extra air directly to the intakes. Also, the Deceleration valve remains closed until a high vacuum of ~17” opens the deceleration valve due to the closing of the throttle plate during deceleration. The decel valve Bosch p/n 0280160324 installed in my car test normal. It is closed until a high vacuum is applied to the vacuum port. I believe we can also agree that the Auxiliary Air Valve (AAV) is a second source of bypass air and it is normally open at start and immediately closes when the engine starts and the intake air reaches a vacuum of ~ 5-6”. The Porsche p/n is 91111027301 and has been superseded by p/n 911110273AX. The Bosch p/n is 0280160405. Since I do not have this part installed I could not test functionality. The part I have installed is Bosch p/n 0280160404. The valve tests normally open at rest and I do not have the capability to draw a large enough vacuum on the large port to draw the rubber diaphragm to close the valve. I did apply air pressure to the vacuum port and the valve closed. In essence it operates like an AAV but I do not know how much vacuum is actually required at the intake runners to pull the rubber diaphragm closed. The vacuum port in my opinion functions like the air hole in the correct part to equalize air in the external chamber. The third source of bypass air is the Auxiliary Air Regulator that is open at cold start and slowly closes while warming up. My goal is to understand why this part was installed and does it function as the correct part does. In my testing it acts like an AAV and not a Deceleration valve. I know that I have seen other motors with this same type of configuration in other posts. Was it because it functions the same and it saves the exorbitant cost for a new replacement part. Yes, used parts can be procured cheaply and I will probably take you up on your offer but first I would like to see if someone can provide any answer to my nagging questions. My last thought is this part has been in my car since I bought it in 1991 with no noticeable impact to the functionality of the CIS system. If it really is functioning as an AAV then why replace it.
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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12-12-2020, 08:35 AM
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CIS Analogy.........
Pat,
It is nice to find someone like you spending time to know and understand how the different CIS components work in tandem with each other parts. You probably have seen a few times in this forum people used a decel valve in place of AAV (auxiliary air valve). And yours is a good example. I don’t know whether you installed it or someone before you did it. Who ever did the installation probably did not realize or understand how the DV and AAV works. They are not interchangeable and if you doubt it, start your investigation. That is how I learned to understand almost every single CIS components in my engine/s. Test and confirm. Tony |
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12-12-2020, 09:14 AM
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Heck, I’m only 5 not 71!
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Tony,
I agree with your assessment that there have been cases where a decel valve was used to replaced a AAV. In essence eliminating the AAV function from the system since the decel valve will always remain closed as long as a vacuum is not applied to the vacuum port. I still have the conundrum of why the 0280160404 valve I have is open at rest and can be closed by added pressure to the vacuum port. As we both understand it, the decel valve is closed at rest and will remain closed until a vacuum is applied to the vacuum port. In the case of the 404 valve it is acting directly opposite of a decel valve at rest and I don’t have the capability to apply vacuum in significant quantity to see if the valve closes under vacuum on the large ports. I will pm you about the offer of a replacement Thanks, Pat
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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12-12-2020, 10:58 AM
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Bosch 0-280-160-404........
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Pat, I did some testing today using 6 Bosch 0-280-160-404 and found out that they work as the typical AAV-400 used in 911 CIS but without vacuum applied to the nipple. The -404 could be used in lieu of AAV-400. Since your -404 is not working, why not replace it with the conventional AAV-400 which is abundant. Tony |
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12-12-2020, 05:51 PM
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Join Date: May 2004
Location: Boulder, Colorado
Posts: 7,275
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Pat - that is the most lucid explanation of the three A valves I have seen. The AAR is the only one whose functions I have been able to memorize. When I had my CIS all apart I was able to do go/no go testing on each of the other two to verify they weren't leaking, but never put it all together. Maybe now I will remember.
Doesn't a Mityvac or other brake vacuum bleeder produce enough vacuum for the test you need? That's the only source of vacuum in my tool assortment, but not expensive and readily available even if usually purchased when searching for a different brake bleeding system. |
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12-13-2020, 03:16 PM
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Heck, I’m only 5 not 71!
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Walt, I was able to use my brake vacuum bleeder to test and verify the function of the decel valve. No issues with it. I have a Bosch valve with a vacuum port p/n 0 280 160 404 installed where a AAV with Bosch p/n 0 280 160 405 should be installed. The 404 is open at rest just like the 405 and if you put a vacuum on the 404 port the valve remains open. My theory is that the valve will close like the 405 valve and the vacuum port acts like the air vent hole on the 405. I just don’t have the capability to cause enough suction on either of the two ports on the 404 to see if it will close.
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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12-13-2020, 05:18 PM
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Heck, I’m only 5 not 71!
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Walt,
Just after I posted my response to you I had an idea that I might get enough suction out of my rigid shop vac with the addition of some reducing adapters. I was able to verify that my Bosch 00 280 160 404 with the vacuum port is open at rest and closes as soon as suction was applied to the larger of the two ports. The shop vac started to labor due to the closing of the valve and the valve opened as soon as the vac was shut off.
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Pat Henry Targa80 1980SC Targa (Mocha Brown) |
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12-13-2020, 05:42 PM
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Mity Vac hand pump.........
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Pat, I use a Mity Vac hand pump to test AAR’s and decel valves (see Post #6). Tony |
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12-13-2020, 07:28 PM
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Porsche
Porsche
