Re: AOS repair

Hey guys. I'm getting the puff of smoke on start-up and acceleration, along with a rough idle, so I believe my AOS is going after turning 80k just a week or so ago on my 2000 Boxster. 2 questions.

1. I have to drive about 50 miles (mostly interstate) to the repair shop. Do I run the risk of further damage? Mechanic gave me the politically correct answer and said it was up to me, but that if the bellows went, and it gulped some oil at 3000 rpm, it could be very bad. Several years ago, on a spirited mountain drive, I was behind JG for several miles with his failing AOS, and all was fine, so just want some opinions.

2. Does $330 out the door sound pretty fair for the repair? Believe that included a little cleaning of the MAF as well. Not looking to nickel and dime this shop, just curious.

Thanks,
Clam

early in the failure cycle its tiny amounts of oil that yield large amounts of smoke. The only potential damage is fowling the cat with oil smoke, but that's a very small, gradual process and i would imagine would take 10s of 000s of miles at your usage rate to do damage. There are cars out there burning 1 qt/1000 for their entire lives. When mine went oil use was not measurable.

As to the repair The part is about $100 - maybe $115 with his fair profit. That leaves $215 for labor. It took me 3-4 hours in my garage. Figure it will take him 2 or less. At $100/hour, which is low these days, that's on the money. Getting at all the various parts is a bit of a pain - the job requires that 3/4 of the work be done from the top, but the other 1/4 from the wheel well, blind. That ,means time going from on position to the other.

Somewhere in the archives i did a write up with pictures.

Like this one:

[i44.tinypic.com]

Yea, that's the access. Nice, huh? That's a cable operated hose clamp on a clamp and AOS you can;t see.

Grant

gee-lenahan-at-gee-mail-dot-com

Grant

gee-lenahan-at-gee-mail-dot-com

Sorry to fog you buddy!

After our mountain drive, I think I parked the car and left it until I replaced the AOS. For 50 miles of steady speed interstate driving, you should be OK. It doesn't sound like yours is that far gone.

IIRC the part costs $100-125ish at retail. Your mechanic should be able to purchase the part for less. Do you know what his standard labor rate is? $80/hour maybe? That would probably work out to around 3 hours time, which is probably what it took me to replace mine, but again I would expect an experienced mechanic with all the right tools to be able to do it in half the time. I am sure that Porsche has this repair in its standard labor table, and 3 hours might be high, but not excessive.

If he is going to do some cleaning - then he should be focusing on the hoses that connect to the intake system and also cleaning the intakes - that is where the oil accumulates.

Yours was not smoking that bad on acceleration. Plus, I could rarely get close enough to you to have any effects from it

Never forget that first mountain drive with you guys. Glad I have video of my wife screaming through the curves on that one, and appreciate y'all including us. Anybody getting together anymore that you know of?
Thanks for reply.
Clam

I just paid the same amount to have the AOS replaced on my 2002 that just turned 100k and I considered it well worth it. I am sure I could have done it myself with all the great write ups, but everyone seems to comment on poor access and what a pita it is, so I thought the couple hundred in labor was fair.
Regarding driving, I am sure mine was failing for a few months before I brought it in, but I saw almost no smoke on start up until the 2-3 days before I brought it in. It smoked every day, so I drove it 20 miles to the shop without issue. If the smoking just started or is minimal, you should be OK.

A lack of smoke does not mean no burning oil. The insidious thing is that once warmed up, the catalytic converter cleans up the blue smoke (up to a point) and in the process ruins itself. but I agree that in early days the amount of oil getting through is very small and perfectly OK.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

... fair.
Here are the DIY instructions: [pedrosgarage.com]
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

I'd always heard that a big enough tear in the AOS could allow enough oil into the intake that once into the cylinder and a compression attempted bad things would happen. Not true?

I suppose anything is possible. But many AOSs fail, and oil usage ( as measured at the dipstick, for those of us who have them) is unmeasurable. That small amount really can;t hydro-lock anything.

However, i would worry about a constant stream of oil ruining some very expensive catalytic converters, that might have no more surface area un-fouled to catalyze.

The AOS sprouts out of the top of the crankcase. Vapors, with lots of stuff in it, goes up. heavy stuff falls back, supposedly, while air passes through. Now, as the membranes fail, you have oil-impregnated air rising through it, over the top and down the other side, and into the intake tract. How much oil can make that trek?

I don't know, but it does not sound like all that much to me.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

is possible.

As I think I mentioned when my car had its first AOS go bad -- though I was not aware of this at the time but learned as soon as I spoke with the SM -- I was told to not drive the car. I could if I wanted to but I decided to play it safe. Besides what's in it for a SM to make this up? Porsche doesn't have a a tow truck operations sideline. It is bad enough the car has a serious problem. Why would he compound it by in my case having me face a 40+ mile tow? I'm sure if he could have he would have said: "Oh yeah, the AOS. No problem. Drive it on in and we'll get the car in the shop and fixed right up for you."

There is too the issue of if he had told me this my drive in might have encountered traffic, or I might have decided to run a quick errand. I mean 'drive it on in' isn't that restrictive.

Now had I known at the first signs of trouble: hunting idle, slight hesitation off idle, oily TB; I might have managed to drive the car safely the 40+ miles to the dealer.

But by the time I called the dealer I had self-diagnosed the engine to a dead end and the engine was now running worse than ever. At some point it began smoking constantly.

That's when I realized while the engine might be ok, after being fixed, I was not in a position to fix it. In fact now that I recall I had decided it was the swirl pots or perhaps a bad scavenge pump. It was the SM who brought me up to speed on the AOS. Which it proved to be.

I had to run the engine to position the car to get it on the flat bed. At the engine the engine was smoking like never before and running rough. As the car was being winched up on the flat bed there was dark fluid coming from the exhaust pipe. Water? Or oil? I didn't have the presence of mind to check. I was just glad the car was on the truck without any engine failure.

Anyhow, later when I called for an update on the car and relieved to hear the car was ok (I thought I was facing a blown engine) with some pressure off of me then we got to talking about this AOS and issues arising from it and I was told about the owner of a car very much like mine who insisted on driving his Boxster while the parts came in. The SM advised him not to drive the car but this owner insisted and the engine suffered a major lock up. I do not know what the outcome was.

In fact, the SM admitted my car's engine suffered a mild lock up as the tech performed a compression test. I have to believe this was the result of the dousing of oil the engine/intake manifold received from that last run. Now had I been going down the freeway at say 3K rpms the engine might have suffered a lockup. It is one thing to have an engine lock up with a starter turning the thing over at under 100 rpms it is another thing entirely to have the engine lock up at 3K rpms.

At the time I was just thankful my car came out of the shop with a new AOS and no damage. (I was also thankful that the trip out to CA for a job interview turned into a job.)

BTW, not every cylinder has to fill with oil. Just one. And it doesn't have to be the cylinder's nominal volume based on the engine's displacement. In the case of my 2.7l it doesn't require 1/6th of 2.7l or 0.45 liters of oil. All it requires is about 39 cu cc or about 1.3 ounces of oil. This is the approx volume of the combustion chamber when the piston all the way up. Remember the chamber's volume is quite small which comes from that wonderful 11.3:1 compression ratio.

How much is 39cc of oil? IIRC roughtly a couple of tablespoons of oil.

Oil hydrolock of an engine with a bad AOS that is allowing oil vapor and maybe because of the failure mode oil vapor particularly heavy with oil vapor past into the intake is a very real possibility.

That's catching it VERY late. Early on, you get a puff of smoke under extreme circumstances (or bad/good luck). The next puff may b months later, but you know. Mine was a violent track act. From what i'm told by experienced porsche racers, a blue cloud can be generated by as little as 2-3 drops of oil that go directly into the mixture of a running motor. A tiny, tiny fraction of 39ml.

So yes, once its fouling things, its a bit late to drive, and damage is already being done ( ha been for months likely) to the cat.

The key is to not let them get that bad. I had no detectable oil in my intake. Car ran perfectly. Never saw smoke unless i saw a LOT.

I'm sure a year later the story would have been different. Although i still think the degrade slowly, and if you're worried about riving it now, you should likely have been worried for the past year.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

to billowing copious amount of smoke in way under 50 miles of driving -- in fact just a few miles when for instance after cleaning the MAF I took the car out for a brief test drive -- and after mainly mostly minutes of idling.

In the 2nd failure the CEL would come at the end of the day after driving all day on freeway speeds. I left the Livermore area and the first CEL event occurred in Flagstaff. The 2nd a day later in Albuquerque. The 3rd somewhere in OK. I made it to my destination in mid-Missouri where after spending the night in a hotel the final event occurred upon the engine's first start of the day when the engine emitted copious amounts of oil smoke.

My point in the 2 above cases is the AOS can go from 'ok' to 'fail' in a brief time. Once you set out there's a tendency to press on which if the AOS fails could lead to serious consequences. Besides you believe you may have some warning but you may not.

In the first AOS failure -- though I didn't know at the time it was the AOS -- I contacted the SM and he told me the symptoms sounded like AOS failure and advised me against driving the car any. I learned later another owner (same color of car and I spotted the car on the lift next to mine later at the dealer) insisted on driving his car until the parts came in and his engine suffered hydraulic lock up.

I was told mine suffered this mildly in the service bay as the tech was running a compression test before replacing the AOS but the low torque/speed of the starter motor was not enough to cause any damage to the engine which has covered 180K miles since with no apparent after effects from this lock up.

In short in spite of what you are being told by others I would urge you to reconsider and have the car flat bedded to the shop for the AOS repair. In my opinion the risk of driving the car is just not worth the small tow bill.

45 min of highway speeds has me a little worried. Just need to price it out. Curious, which would be cheaper , if either: Use a company where the shop is , or use someone I know from my city to take it up there.

Thanks again.
Clam

It was around a 90 mile tow. I had to pay for the tow over the 1st 5 miles.

In the case of the 1st AOS failure I asked the SM to recommend a tow truck company and used that one. That is about all I remember from that tow.

In the case of the 2nd failure I think I ended up with a local tow truck operator -- again arranged through my auto club. I prefer to use a local tow truck operator provided of course that he is knowledgeable about these cars to be sure but also because a local operator shows up quicker and we get the car loaded up and on the road quicker.

If you use one from where your destination is he has to drive a ways before he gets to your car and I hate to stand beside a sick car any longer than I have to waiting for a tow truck.

Oh, in the case of the 2nd tow based on my experience with the 1st AOS failure when I filled out the envelope prior to putting in the keys and dropping the envelope into the drop box I wrote on the envelope in big black letters: AOS! DO NOT START ENGINE! and took a pic of it just in case some lazy lot helper wanted to cut corners.

Later I talked to the SM and he told me they never start cars even though in my car's case since the dealer was closed it had to be left on the side street just off the dealer's properly. A team of techs goes out with the SM and pushes the car in to the service area.

My 2002 Base at 75k needed a Motor Mount and a AOS (check engine light, rough idle, smoke on start-up)....$950.00 out the door at my local Porsche dealer.

All was fine, two days later Check Engine light back on!!!

Any thoughts?

Quote
gregsterInMO
My 2002 Base at 75k needed a Motor Mount and a AOS (check engine light, rough idle, smoke on start-up)....$950.00 out the door at my local Porsche dealer.

All was fine, two days later Check Engine light back on!!!

Any thoughts?

Could be a couple of things. One is the bad AOS represented an intake air leak. The DME adapted as it is supposed to do. If the bad AOS is replaced and the DME adaptation was not reset -- via clearing the DTC codes (even if none are present) -- upon engine start and subsequent running with the new AOS the DME might trip an error as it crosses some threshold in undoing what it learned with the bad AOS. Given the delay in the CEL appearing I would tend to dismiss this as what is going on in your car's case.

Another possibility is if the AOS fed the engine oil this can take some time to work its way out of the engine. Specifically the TB and intake manifold can get rather oily.

At the first AOS failure me SM told me it can take up to 50 miles of driving before all of this has worked its way out of the engine. He drove the car -- I was out of town -- and the CEL would come back on. I finally traced this to a bad O2 sensor. It might have been pushed over the edge from the oil bath it got from the AOS failing. Though since none of the others went bad I attribute this one bad sensor to coincidence.

Not directly related to the AOS yet another source of a CEL is a leaking oil tube filler cap.

There is the MAF of course. I've had one go bad.

There is too a possibility that the repair was not done right and there's a hose leaking or even the new AOS is bad out of the box.

But really the error codes are needed to have something better to go on.

for free from your local auto parts store. Post the code here and we will give you an opinion.

The alternative is to bring it to the dealer and have them do it but then you don't get the benefit of collective knowledge before you choose the best course of action.

..which in a street driven car is easy to do, since the cats clean-up the exhaust once they are warm. I've watched a lot of AOSs go, and typically it runs for weeks to months with very little/slow degradation. Then again, track use shows it up very early....

Mine was a huge blue cloud on downshift on a hard left hand turn, followed by........nothing. Ran the car for 3 months before doing AOS.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com



Edited 1 time(s). Last edit at 11/16/2012 10:57AM by grant. (view changes)

When my AOS went out there was so much smoke that it would have been unsafe for me to drive even a block. I had my car towed. Dealer said RMS needed to be replaced because the AOS went out. Forgot the reasoning, but somehow they're connected. When they got to the RMS, they inspected the clutch and recommended it be replaced to save on labor. They also recommended I get the LNS IMS bearings. So....the AOS failure ended up costing me thousands....

Quote
boxsterd
When my AOS went out there was so much smoke that it would have been unsafe for me to drive even a block. I had my car towed. Dealer said RMS needed to be replaced because the AOS went out. Forgot the reasoning, but somehow they're connected. When they got to the RMS, they inspected the clutch and recommended it be replaced to save on labor. They also recommended I get the LNS IMS bearings. So....the AOS failure ended up costing me thousands....

seals like the RMS (or even the FMS and there are others) in that the low pressure pulls the seal lips in and they do not recover. They might provided sufficient over pressure was created but that's tricky to do and not to overdo it. Other seals/gaskets -- like the camshaft cover -- could be compromised for the sake of a fairly simple RMS.

As an aside, a camshaft cover reseal for example can be as expensive as a tranny drop/RMS job. Also, this supposes the camshaft cover develops an external leak. If it develops an internal leak there is no outward sign but oil pressure to one or more camshaft bearings, and other valve gear under that camshaft cover, could be is reduced and serious engine damage can result. If for instance a camshaft bearing burns up (so to speak) this requires a new head as the camshaft cover is part of the head, machined as part of the head assembly. YOu think a RMS is an expensive repair. Price a new had for your car's engine.

Anyway, that would have to be some spectacular AOS failure. Even though my car's AOS was so bad and allowing so much low pressure in the crankcase I could not remove the oil filler tube cap and the engine was smoking like I don't know what, the RMS was just fine. Now it was a "new" one having been installed at 25K miles, about 55K miles prior to the AOS failing. Could be the RMS in your car's engine was a subpar seal to begin with and less able to withstand/tolerate the low pressure and this just sent the seal over the edge.

Since there is always a path for air -- even with a new AOS, i dont get it.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Quote
grant
Since there is always a path for air -- even with a new AOS, i dont get it.

Grant

through the intake and under pressure so the crankcase doesn't get subjected to the full low pressure the intake manifold has at certain times.

When the AOS fails while the engine could be subjected to over pressure -- though I suspect there is a fail safe to avoid this since this is the more serious of two evils -- it can certainly be subjected to under pressure. This is also I believe intentional -- or a beneficial side effect -- as this gives the driver an early warning something is amiss. There is an intake leak and this makes itself known. I remember my car's 2nd AOS over 2K miles of driving over several days the CEL came on at least once per day and had I followed the guideline to get it to a dealer for attention the AOS would have been found going bad or bad and dealt with. I believing the problem was MAF related drove on. Only when the first start of the day had the engine smoking continuously did the real meaning of the CEL and associated error codes become obvious.

My old Boxster has been getting a CE on and off for something like the past year and the nearest indication has been to replace O2 sensors, and at least one on each side has been. A few years ago before I sold the car, they were all changed out in fairly short order. I don't recall the current codes, but maybe yours might help my friend (who now owns the 986) determine if a marginal AOS is the issue.

Minus 40 degrees... Is that Fahrenheit or Celsius?

Quote
Laz
My old Boxster has been getting a CE on and off for something like the past year and the nearest indication has been to replace O2 sensors, and at least one on each side has been. A few years ago before I sold the car, they were all changed out in fairly short order. I don't recall the current codes, but maybe yours might help my friend (who now owns the 986) determine if a marginal AOS is the issue.

or when the oil filler tube cap was leaking.

In both instances though the error codes hinted at mixture/fueling problems which had me thinking MAF though I remember that.

In the case of the cap the resulting error codes were at some times indicating a lean problem but once in a while a rich problem. I was convinced it was the MAF. A dealer tech also after a told him what I was seeing offered "MAF". I'm pretty sure though had I had the car looked at the tech would have spotted, heard the cap leaking.

In yet a 3rd instance in which the MAF did prove to be bad I can't recall the error codes now but I do recall the short term fuel trims were swinging rail to rail which suggested the MAF was at the root of the problem. I might have disconnected the MAF to see if the behavior changed but I can't remember for sure. What I do recall is I swapped out the MAF and it proved to be the MAF thoiugh this might have been a lucky guess helped by the fact I had an old MAF that had replaced when the real problem was the oil filler tube cap leaking.

I might point out the time O2 sensors proved to be bad the error codes pointed to them explicitly. I just wanted to be sure and wanted to catch the sensors acting up and I finally did.

Anyhow, what are the error codes your old Boxster is producing?

Minus 40 degrees... Is that Fahrenheit or Celsius?

Grant

gee-lenahan-at-gee-mail-dot-com

Got it up on flatbed and saw that both rears are showing bars,....so about to click the tire rack banner