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Old 09-08-2019, 09:45 AM   #1
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Vacuum leak - smoke test shows smoke coming from under the air oil sperator

Does that mean the AOS needs to be replaced? Or is there a hose underneath there? I cant really tell exactly where it is coming from.
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Old 09-08-2019, 10:34 AM   #2
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Upon further inspection, I think it is the air oil separator boot that has come off underneath.

Has anyone replaced this before? Any tips?

There was a screw type hose clamp on it so I think that means somebody has messed with it before. Not a spring type hose clamp.
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Old 09-08-2019, 11:04 AM   #3
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Originally Posted by Vtx531 View Post
Upon further inspection, I think it is the air oil separator boot that has come off underneath.

Has anyone replaced this before? Any tips?

There was a screw type hose clamp on it so I think that means somebody has messed with it before. Not a spring type hose clamp.
I replaced my AOS just a short while ago. It does have a boot that attaches from the bottom of the AOS to the engine. Yours has been replaced as evidenced by 1. The worm drive clamp, and 2. That's the newer AOS part. The newer AOS round piece on the top is vertical while the older part round top is horizontal. That said... when I removed my old AOS that bottom boot was like butter and, because I was replacing in... I just tugged at it and it came right off. When completely I pulled off the old one I just removed what was remaining of that boot.
See if you can source that boot for a better price (https://www.ebay.com/p/Porsche-Oil-Separator-Boot-996-Carrera-986-Boxster-Genuine-99610723752-Bellows/1822097375?iid=323690532260&chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=323690532260&targetid=800915196857&device=c&mktype=pla&googleloc=9031411&poi=&campaignid=1497794122&mkgroupid=56281259685&rlsatarget=pla-800915196857&abcId=1139466&merchantid=114749148&gclid=EAIaIQobChMIveC3oPXB5AIVgZOzCh2hEQwMEAkYBCAB EgKnVPD_BwE) and, after removing the rear wheel and shroud... go to town on it. Shouldn't take but 30 minutes jacking up the wheel.... removing shroud... removing old... installing new... reinstall shroud and wheel and your good to go.
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Old 09-08-2019, 11:22 AM   #4
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Pretty sure I've got one of these floating around in a box someplace, still in the bag. It's yours for postage, if I can find it.

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Old 09-08-2019, 12:48 PM   #5
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Upon further inspection, I think it is the air oil separator boot that has come off underneath.

Has anyone replaced this before? Any tips?

There was a screw type hose clamp on it so I think that means somebody has messed with it before. Not a spring type hose clamp.
This happened to my Boxster at the race track last month. Doesn't matter if its the OEM spring or an aftermarket screw type, the fix is the same - just re-attach the tube/boot and make sure that the clamp is fully engaged to hold it in place.
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Old 09-08-2019, 05:11 PM   #6
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I replaced my AOS just a short while ago. It does have a boot that attaches from the bottom of the AOS to the engine. Yours has been replaced as evidenced by 1. The worm drive clamp, and 2. That's the newer AOS part. The newer AOS round piece on the top is vertical while the older part round top is horizontal. That said... when I removed my old AOS that bottom boot was like butter and, because I was replacing in... I just tugged at it and it came right off. When completely I pulled off the old one I just removed what was remaining of that boot.
See if you can source that boot for a better price (https://www.ebay.com/p/Porsche-Oil-Separator-Boot-996-Carrera-986-Boxster-Genuine-99610723752-Bellows/1822097375?iid=323690532260&chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=323690532260&targetid=800915196857&device=c&mktype=pla&googleloc=9031411&poi=&campaignid=1497794122&mkgroupid=56281259685&rlsatarget=pla-800915196857&abcId=1139466&merchantid=114749148&gclid=EAIaIQobChMIveC3oPXB5AIVgZOzCh2hEQwMEAkYBCAB EgKnVPD_BwE) and, after removing the rear wheel and shroud... go to town on it. Shouldn't take but 30 minutes jacking up the wheel.... removing shroud... removing old... installing new... reinstall shroud and wheel and your good to go.
Very informative thank you. It seemed like the boot was extremely pliable (that what you meant about butter) and very loose on the mounting. Like if I reused it would be similar to having pants that are way too big and then you cinch up the belt really tight - doesnít work well.

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Pretty sure I've got one of these floating around in a box someplace, still in the bag. It's yours for postage, if I can find it.

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That would be great! Let me know


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Originally Posted by thstone View Post
This happened to my Boxster at the race track last month. Doesn't matter if its the OEM spring or an aftermarket screw type, the fix is the same - just re-attach the tube/boot and make sure that the clamp is fully engaged to hold it in place.
Glad to hear it sounds like not a really bad job thanks.
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Old 09-09-2019, 10:21 AM   #7
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I replaced my AOS just a short while ago. It does have a boot that attaches from the bottom of the AOS to the engine. Yours has been replaced as evidenced by 1. The worm drive clamp, and 2. That's the newer AOS part. The newer AOS round piece on the top is vertical while the older part round top is horizontal. That said... when I removed my old AOS that bottom boot was like butter and, because I was replacing in... I just tugged at it and it came right off. When completely I pulled off the old one I just removed what was remaining of that boot.
See if you can source that boot for a better price (https://www.ebay.com/p/Porsche-Oil-Separator-Boot-996-Carrera-986-Boxster-Genuine-99610723752-Bellows/1822097375?iid=323690532260&chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=323690532260&targetid=800915196857&device=c&mktype=pla&googleloc=9031411&poi=&campaignid=1497794122&mkgroupid=56281259685&rlsatarget=pla-800915196857&abcId=1139466&merchantid=114749148&gclid=EAIaIQobChMIveC3oPXB5AIVgZOzCh2hEQwMEAkYBCAB EgKnVPD_BwE) and, after removing the rear wheel and shroud... go to town on it. Shouldn't take but 30 minutes jacking up the wheel.... removing shroud... removing old... installing new... reinstall shroud and wheel and your good to go.
AOS diaphragm has been vertical since 1998
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Old 09-09-2019, 10:44 AM   #8
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AOS diaphragm has been vertical since 1998
I replaced my AOS a while back... and it was horizontal. The new/updated one I installed the diaphragm was vertical.

Did Porsche come out with that update the same year of production? Was the car manufactured with both versions? I'm curious.
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Old 09-09-2019, 12:51 PM   #9
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Pulled the AOS today. Pretty easy job. The lower hose quick connector was already broken from the last guy (he owned a shop) but it seems to be sealing fine.

I inspected the bellows and besides the fact that it seems out of shape (maybe from heat) I was able to reinstall and tighten a screw type hose clamp but I don’t like the fact that there is no lip on the metal fitting the bellows goes on to. Seems like it can easily come off again in the future.

The AOS was a uro parts one so obviously replaced before. Previous owners used cheap parts all over this car. For example the brake rotor hats are all rusted. Annoying.

Smoke test after was good. No smoke and the system seemed like it was holding a bit of pressure.

I pulled the negative terminal of the battery to try and reset the ECU. Let it stay disconnected for about 10 mins. When I reconnected it the car ran really rough, missing and knocking a bit (through the intake). I would have though that would reset the fuel trims and it should have ran a lot better initially? Ended up smoothing out after a minute and runs good now. No check engine light yet.

What is the proper way to reset fuel trims or ecu on this vehicle?

I think I’ll leave the uro AOS in there but maybe put on a OEM bellows. Any opinions? There was a little bit of oil in the intake but no smoke out the exhaust.
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Old 09-09-2019, 04:07 PM   #10
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AOS diaphragm has been vertical since 1998


This was the type, horizontal, that I removed from my car replacing it with the newer/most current part, vertical. I had read that the horizontal diaphragm would often quickly fail on the horizontal model, so the part was modified with the diaphragm vertical.

Are you saying that when the car was manufactured the factories were installing both versions?

Thank you.
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Old 09-10-2019, 07:41 PM   #11
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I pulled the negative terminal of the battery to try and reset the ECU. Let it stay disconnected for about 10 mins. When I reconnected it the car ran really rough, missing and knocking a bit (through the intake). I would have though that would reset the fuel trims and it should have ran a lot better initially? Ended up smoothing out after a minute and runs good now. No check engine light yet.

What is the proper way to reset fuel trims or ecu on this vehicle?
Its normal for the engine to run like crap for a bit after resetting the ECU. Resetting the ECU also resets the fuel trims. The ECU will continue to vary the fuel trims as you drive in varying conditions (cold, warm, hot, idle, mid-throttle, full throttle, etc) to find the optimal settings.
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Old 09-11-2019, 04:22 AM   #12
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This was the type, horizontal, that I removed from my car replacing it with the newer/most current part, vertical. I had read that the horizontal diaphragm would often quickly fail on the horizontal model, so the part was modified with the diaphragm vertical.

Are you saying that when the car was manufactured the factories were installing both versions?

Thank you.
BYprodriver, did I stump you or are you still scouring the interwebs looking for the content that will substantiate your claim?
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Old 09-11-2019, 07:47 AM   #13
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BYprodriver, did I stump you or are you still scouring the interwebs looking for the content that will substantiate your claim?
No it's called hands on experience.
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Old 09-11-2019, 09:09 AM   #14
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No it's called hands on experience.
Oh, I know. I know you know I know you know your ****************. You're on my go-to list when I run a search. Several times I've pulled up a bookmark referencing your particular-scenario advice and recommendation, and they haven't failed me. 986 members following your advice have, collectively, saved... at least $1,000,000. At least.

My hat is off to your wisdom.
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Old 09-11-2019, 10:48 AM   #15
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I replaced my AOS a while back... and it was horizontal. The new/updated one I installed the diaphragm was vertical.

Did Porsche come out with that update the same year of production? Was the car manufactured with both versions? I'm curious.
I believe it was phased in late 1998.

My Motorsport AOS has a horizontial diaphram.
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Old 09-17-2019, 05:28 AM   #16
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Well, check engine light came back on. Reason being - the boot slipped off again. I didnít think it would last long. How is there not a retaining lip molded into the mounting on the engine? Grrrrr
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Old 09-18-2019, 06:13 AM   #17
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See this thread... AOS - 2 diff models - boot/no boot - which year is which?
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