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.

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=80091519685 7&device=c&mktype=pla&googleloc=9031411&poi=&campa ignid=1497794122&mkgroupid=56281259685&rlsatarget= pla-800915196857&abcId=1139466&merchantid=114749148&gc lid=EAIaIQobChMIveC3oPXB5AIVgZOzCh2hEQwMEAkYBCABEg KnVPD_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.

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.

Sent from my SM-G970U using Tapatalk

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.

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 - doesn’t work well.

That would be great! Let me know


Glad to hear it sounds like not a really bad job thanks.

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.

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.

http://986forum.com/forums/uploads02/AOS1568073798.jpg

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.

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.

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.

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. :cheers:

I believe it was phased in late 1998.

My Motorsport AOS has a horizontial diaphram.

Well, check engine light came back on. Reason being - the boot slipped off again. I didn’t think it would last long. How is there not a retaining lip molded into the mounting on the engine? Grrrrr

See this thread... http://986forum.com/forums/performance-technical-chat/76231-aos-2-diff-models-boot-no-boot-year.html#post603393

Replaced AOS with genuine Porsche unit. CEL is back P1126 P1133. Maybe another smoke test is in order but it seems like it is cutting out and hesitating when under load and snapshot showed CEL triggered at 18.8% load.

Any thoughts? Perhaps I need to run some graphing software to see what is going on at higher loads?

Latest snapshot:

P1126
Sys1 CL
Sys2 CL
Load 18.8%
ETC 187 degrees
Sft1 19.5
Lft1 28.9
Sft2 18.0
Lft2 26.6
Rpm 2440
Vss 45

Prior to replacing AOS and resecuring the boot I was getting P1128/P1130 triggered with P1126/P1133 pending.

Prior snapshot:

P1128
Sys1 CL
Sys2 CL
Load 2.0%
ETC 226 degrees (had overheating issue that is now fixed)
Sft1 -3.9
Lft1 14.1
Sft2 -4.7
Lft2 13.3
Rpm 680
Vss 0

The original code/snapshot looks like a classic vacuum leak but the new one maybe a MAF sensor?

Any help appreciated!

What year is the car?
Miles?

2001 100,000 miles

Your current snapshot and the fact that you have hesitation under load suggest a vacuum leak.
I would buy a vacuum gauge (about $20.00 at most auto parts store). and do an intake vacuum test. Should read 18-22 on the gauge with a steady needle at idle.
That will prove out yes or no on the possibility of a vacuum leak problem.

If you suspect a faulty MAF sensor unplug it. Take the car for a short drive and see if that improves engine performance. If it does then the MAF is faulty, if it doesn't then most likely the MAF sensor is not the problem. But the wiring to the sensor could be.


Your latest work on the AOS could be related to your current codes. double check your work. Make sure everything is connected correctly and that you didn't knock some wiring or vacuum hose loose in the area of your work.

Since your car is a 2001 it has E-gas throttle (drive by wire) after you disconnected your battery did you recalibrate your throttle when you reconnected the battery???? Before starting the car.????

I did not recalibrate the throttle. How do I do that?

After replacing the AOS I just cleared the codes. Then it idled extremely poorly for about 60 seconds and then smoothed out.

Is there a specific place that I should connect the vacuum gauge?

I thought hesitation under load would suggest something other than a vacuum leak because there is minimal vacuum with the throttle open?

Seems odd to me that the fuel trims would be worse now! About +50% total seems pretty extreme and I don’t know if a MAF sensor would be that far off. At last not just from being dirty I wouldn’t think. I need to pull it and see if it is a cheapo crap brand like the other parts that have been replaced by the PO in the past.

I scanned it with live data at idle. Unfortunately my free software doesn’t graph the data. Any suggestions for software for Porsche?

858 rpm
Load 3.5%
Advance timing +8 degrees
Closed loop
Stft1 -7.03
Stft2 -9.38
Ltft1 +31.25
Ltft2 +31.25
MAF 5.00 g/s

Nothing visibly wrong near the new AOS

To recalibrate your throttle: I would disconnect the battery for say half an hour. Then reconnect battery.
Turn key to on position for one full minute:
Do not start:
Do not touch throttle:
After one full minute turn key off for at lest ten seconds.
Start car: let it idle tell the idle smooths out.
Should be good to go.

Yes with throttle open you have minimal vacuum but you are still getting some unmetered air. So your still lean so you can "possibly" get hesitation.

Most vacuum gauges come with a tee fitting and some hose so you just need to find a vacuum hose on the intake that you can tee into.

If vacuum reading is good: other things to look at:
Possible exhaust leak ahead of O2 sensor: (could be drawing 02 into exhaust ahead of sensor)

Fault with the MAF sensor (as you mentioned)
or wiring from the sensor to the DME.
Fuel:
Pressure and volume. I believe there is a Presta valve on the fuel rail that you can hook a fuel pressure gauge to. Usually they have brass cap on them.
I can look up the pressure specs. for you if you need them.

I checked vacuum from the brake booster hose. It was slowly waving up and down between 17.5-18”. Is that acceptable? I did another smoke test and couldn’t find anything.

I unplugged the MAF, didn’t drive it but just revved in the driveway. Seemed to improve but still showing lean condition (you add the numbers together correct?) When revved to 4,000 rpm:

Stft1 -14.84%
Stft2 -16.41%

Ltft1 +31.25%
Ltft2 +31.25%

I removed the MAF and it is a Bosch unit. Looks to be in good shape visually. Not sure how to tell if it is genuine Porsche part or aftermarket Bosch. .00 end of part number so it is not the newest version .01.

I took MAF readings at various rpms and it is a straight line when graphed.

800 4.25 g/s
1400 6.00
2200 9.5
3000 12

Where do I go from here??

Would an exhaust leak affect both banks?

Your vacuum reading is right at the low end of the range but acceptable.
I would unplug the MAF and then take it for a drive to see if it performs differently.

Your long term fuel trims are learned trims based on your short term trims.
So if you have an issue such as a lean condition and then you fix it. It takes some time for the ECU-DME to begin to adjust (Learn the fixed fuel trim) and show as a more normal long term fuel trim.

Going on memory from research here but yes you add the trim numbers together. Bank 1 short and long term added together should not exceed 10 if I remember correctly. same for bank 2.

No an exhaust leak would not affect both banks as the Porsche has twin exhaust manifolds. Sorry brain fart on my part.
Going back through your posts if I read them right you had high positive (no plus or minus sign so I am assuming plus) short term fuel trims before you unplugged the MAF
After you unplugged the MAF you had high negative short term fuel trims. So in my head (oh god) your issue could be MAF sensor.
Unplug it take for a drive see if you still have the hesitation.

VTX531
Question?????
When you did the smoke tests on the car did you remove the MAF sensor?????
They can be very sensitive to contaminants.

I did not, but I removed the pipe between the MAF and throttle body and introduced the smoke at the throttle body.

****I think (hoping) the problem is solved****

I disconnected the battery for about 1 minute, pressed brake, reconnected, and did ignition on for one minute and off for 10 seconds.

This cleared the codes and reset the long term trim to zero. It ran great right off the bat (unlike before when I only cleared the codes using the scanner). Numbers seem good now at idle and when revved.

Idle:
STFT1 +3.13%
STFT2 +2.34%
LTFT1 -0.78%
LTFT2 -0.78%

Not solved!!! :(

I took it out for a drive and could barely make it around the neighborhood. When giving it gas, the short term trims were pegged at +25% and eventually the long term trims settled above 30% again.

Midway through when idling I was seeing:

STFT1 -19.53%
STFT2 -19.53%
LTFT1 +21.88%
LTFT2 +20.31%

Maybe a fuel delivery issue??

Fuel pressure test:

Key on ignition: 42-46 psi. Out of spec. Manual says between 52-58

Idling: 47 psi. In spec. Manual says 46-52psi

When revved in neutral throughout the rpm range the pressure is pretty steady within specs.


Thoughts???

I drove around with the MAF disconnected while monitoring the live data.

It seemed to run better with MAF disconnected. The short trims were going negative 20’s under acceleration and trying to balance out the +32% long trims.

When I reconnected the MAF it was adding more positive fuel to the short trims on top of the +32% long trims.

Bad MAF?

Now I got P0102 code. Is that just from having the sensor disconnected on and off while testing?

I am starting to lean toward MAF sensor issue. You could try cleaning it with a cleaner made for the purpose. I think yours is the wire type like the one in my 2000S. just don't touch the wire. clean it good let it dry. put it back in and watch your trims. see what happens,
I had a CEL on mine a year ago. I cleaned it been good ever since.

not sure what to think on that. in spec on idle is a positive at least it shows that the injectors are getting correct pressure.
under spec. at key on test is the head scratcher. I believe the key on test is to check that the system is pressurizing properly for initial start up. (That is a guess on my part.)

You had not said anything about starting issues so maybe the low spec is not an issue????

That would be my best guess as 0102 is a MAF code.

sorry double post. things like that happen when I only sleep 3 hours a night

Well here is this morning’s tinkering...

I took out the MAF and cleaned it. Reinstalled it and reset the ecu. Short term fuel trims were pegging at +25%. I am guessing that is the maximum it can do. Car had no power, hesitation, ran badly.

Then I unplugged the MAF and it ran great and never go above +10% on the short term fuel trims.

So I am thinking MAF sensor and hopefully it is not an issue with the MAF wiring.

With the MAF plugged in the car runs poor because it is getting a signal or value from the MAF that is wrong or implausible, out of range what ever.
When you unplug the MAF sensor the ECU-DME no longer gets a signal (or value) from the MAF. So the ECU-DME substitutes a value and that forces fuel system to go to a set fuel map. which in turn allows the car to run.
A long way of saying the ECU-DME is recognizing that the MAF signal is missing. So the wiring should be good.
So between the two of us I would say we have pinned it down to a faulty MAF sensor;)
The proof will be when you spend the big bucks and replace it.
Let me know the outcome.

I ordered a Delphi unit from local napa for $100. It was the only one they had in stock. I would prefer Bosch but at least I can try this and see if it fixes the problem. I will be reporting back shortly...

I decided to order the Bosch unit instead. Now I have to wait a few days for shipping. Hope this works.