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Old 01-04-2013, 05:37 PM   #1
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AOS Question

Hi guys,

I did a quick search & couldn't find anything on this specifically. My '01 Boxster started fine today but started smoking out of the tailpipe. I unscrewed the oil cap at idle & it came off easy with barely any change in idle. I did pull a P0420 & P0430 a few days ago.

Any thoughts or suggestions would be helpful.

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Old 01-04-2013, 05:53 PM   #2
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Was it blue smoke or white? Did it maybe get overfilled at last oil change? Check the little return pipe that runs from the AOS to the Intake - If it's oil saturated then too much oil is building up in the AOS and being pushed through...
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Old 01-04-2013, 06:06 PM   #3
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It was hard to tell in the dark what color, I will check it tomorrow but it smelled more petroleum than coolant in nature. It could be oil, when I replaced the starter a few months ago I noted a bit of oil in the TB & intake pipes. I have also noticed the coolant going a bit low in the tank, but again this smelled more petroleum than a coolant smell.
The car has also been sitting with the front on jack stands for some work I was doing up there. Oil change was a few weeks ago & the gauge is 1 segment below full.
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Old 01-04-2013, 06:18 PM   #4
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If at one point or another a bunch of oil got sucked into the overflow channels and filled the AOS to the point of oil getting into your intake, it could take a while to get it all out. If you had the car up on jacks in the front, the pooled oil in the intake could have shifted which will now take a while to burn off. If you can, take the cross tubes off on the intake and clean the TB as well as the intake bodies (it wont hurt anyways) and then watch it for a while to see if oil builds up again in the intake. I had a similiar issue a while back on a car and one of the oil return pumps went belly up.
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Old 01-04-2013, 07:03 PM   #5
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OK, I will try cleaning everything tomorrow. Is MAF cleaner alright to us to do this?
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Old 01-04-2013, 07:45 PM   #6
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Just plain old carbon cleaner and a couple of lint free rags should do the trick. When you get the center tunes off between the two intake manifolds spray some carbon cleaner in each of the openings and wipe them out as best as you can as the oil tends to pool in the bottom. Also take that crossover pipe off between the intake and the AOS, the oil traps in the flex texture of the pipe. Spray it good and then blow it out with the air hose.
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Old 01-05-2013, 06:54 AM   #7
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When the AOS fails you will get a smokescreen worthy of a James Bond getaway scene. Seriously. There will be no doubt when you see it. This can happen at start up but it will happen randomly while you're just driving down the road. By the time you pull over and let the smoke clear, the car will run normally.

Instead if you are seeing a momentary big puff of white/blue smoke occasionally on startup, this is somewhat normal. There can be several causes for this but if it only happens once every 6 months you can probably just live with it.
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Old 01-05-2013, 12:58 PM   #8
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Well I got the TB & crossover tube off & this is what I found. Looks like AOS time?

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Old 01-05-2013, 01:14 PM   #9
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Thats a lot of oil....
Outside of replacing the AOS i would check the extractor pumps in each
head to make sure they are still working as they should... remember when you put them back in that they are the same for both heads but the right side one should have the 1-3 facing the inside (towards the case) and the front one on the left side (drivers) should have the 4-6 on the inside (facing the case)... If you dont have the orientation right the pumps will not extract the oil back to the sump!
If these pumps are not operating right, the AOS unit will flood under high RPM and oil will pass back into the intake regardless if the AOS is working or not. The only thing that happens to a failing AOS is that the membrane splits and constantly allows a vaccum to the intake; but if the AOS fills too much it will spew oil over into the intake no matter what....
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Old 01-05-2013, 04:33 PM   #10
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Started taking the AOS out, figured since I have one on the shelf I might as well change it. Only issue so far is the pipe the the left side of the engine is being a bear to get released from the AOS & there seems to be a electrical connector bracket preventing the last 1/4" of removal. I'm gonna get some rest & tackle it again in the morning.
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Old 01-05-2013, 05:28 PM   #11
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A bit tricky to get out... I usually find taking the oil filler pipe out helps :-)
the biggest pain is putting it back in... If you take the cover plate under the engine out you will gain better access from below to get the lower clamp ring back in :-)
Cut the old AOS open and see if the diaphram is ripped... if not it could be something different....
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Old 01-06-2013, 07:16 PM   #12
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Originally Posted by Bryan topping View Post
Started taking the AOS out, figured since I have one on the shelf I might as well change it. Only issue so far is the pipe the the left side of the engine is being a bear to get released from the AOS & there seems to be a electrical connector bracket preventing the last 1/4" of removal. I'm gonna get some rest & tackle it again in the morning.
Just be patient and make sure you have a cable operated clamp tool.
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Old 01-07-2013, 09:17 AM   #13
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Just be patient and make sure you have a cable operated clamp tool.
no need for the tool if you are patient. Does the tool make it easier? Hell yeah, the majority of the time you will spend on removing the AOS could be spent on removal and installing the clamp, but I R&R about 6 of these so far without too much of a issue as long as I was patient.
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Old 01-07-2013, 04:14 PM   #14
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Healthservices - no pun intended but you'll need health services if you do many of these without the cable clamp tool.... I tell you, without that cable clamp tool they'd be putting me in the nuthouse by now...
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Old 01-08-2013, 09:25 AM   #15
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Healthservices - no pun intended but you'll need health services if you do many of these without the cable clamp tool.... I tell you, without that cable clamp tool they'd be putting me in the nuthouse by now...
Well I have the tool now which is funny as I now use it all the time. In 15 years of being a dealer tech I never used one and always done without. Without the tool I can do most AOS replacements in less than hour, with the tool now I think I can do it in 45 or even less if all the tools are out and ready to go.

Too bad since I had the tool I've only done one AOS replacement
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Old 01-10-2013, 05:13 PM   #16
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OK, I got the AOS changed (not all that bad of a job) & cleaned and as much of the oil out as I could.

Questions I have so far are:

1. Should I run a can of Techron through to clean the remaining oil film in the intakes?

2. Would a failing AOS trigger the P0420 & P0430 codes?

3. Would the car sitting on jack stands for a few days on the front only cause this?
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Old 01-10-2013, 05:28 PM   #17
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The Techron cant hurt and leaving the vehicle propped up in the front for a while shouldnt cause that kind of oil to leak into the intake (unless you had it on a huge angle and running... did you check your pumps?
The 420/430 code usually triggers if the 2 O2 sensors (one in fronto of the cat, one behind the cat) start to read too closely sensing cat failure... BUT... all the oil burning through the system 'could' most definitely cause that....
Get it all cleaned out with the Techron, take it for a good drive (keep an eye on smoke), and then reset the codes, see if they come back... after you drove it for a bit, check the crossover pipe from the AOS to the intake to see if its full of oil again....
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Old 01-14-2013, 02:07 PM   #18
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I took the car for a 120 mile cruise yesterday & it ran great. No smoke, great power & best of all no codes. Oil level is the same, 1 segment below the full mark on the gauge, almost to the upper mark on the dipstick as when all this started.

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