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... on the TT first, just to see , maybe i get rid of the oil in the passenger side turbo hose.
It is very irritating, because if you have stock intercooler hoses, and you have oil build up there, it will sweat thru the hose and eventually drip on the floor.
..
Are you suggesting that oil pooling in the intercooler hoses is normal and expected rather than an indication of leaking turbo seals? Or is the oil from the intake (the crank case breather system?)
On the stumble: fuel injectors? Pulled and examined? Cleaned? Years ago my wife’s 981CS had a terrible WOT stumble that was ultimately one or more badly varnished fuel injectors. One or more injectors with a poor spray pattern will cause poor low-load combustion and intermittently with symptoms one can feel from the driver’s seat.
Mufus,
Thanks for all the info. I noticed that the MAP also gets oil on it when i pulled it out just to inspect it, i cleaned it and thought it may have lessened the stumble a bit but i may have just been wishful thinking because it was definitely there the next morning. I also found the intake vent foam gaskets to be completely shot, and also the stumble happens much more at speed...could the pressure surge of intake air be causing this at lower rpm and higher speed?? i know, kind of grasping at straws. I'm going to change them and see if it helps at all. The only thing i was thinking is that there could be air that is accounted for fluttering past the intake source causing a little hunting for the right mixture.
But...If you can get parts cheaper and are willing to try a few things my biggest bet would be on the primary O2 sensors (the wideband ones) i have a sneaking suspicion that is the culprit. But i haven't wanted to drop 500$ on them without more research on this as it isn't throwing a code and i can't find anything in the data logs that i am doing on m COBB that show this as the smoking gun. Love to see if the sensor just goes out by a small percent and at lower exhaust volume and finer fuel trim levels it isn't able to meter it correctly.
thanks again!!
Dane
Originally Posted by duxsi
Based on feedback from a group of owners (991.1 with the stumble), I can confirm that the following actions did not resolve the issue.
1. Spark plug replacement.
2. Pre Cat O2 Sensors replacement.
3. Throttle Body replacement.
4. High Octane fuel.
I hope this saves my brethren a few $$..
Also add to this list replacing the VVS ( variable valve sistem ) actuators. Same result.. nothing.
Are you suggesting that oil pooling in the intercooler hoses is normal and expected rather than an indication of leaking turbo seals? Or is the oil from the intake (the crank case breather system?)
I talked about this including with SamboTT who said to keep the oil level to medium. Not maximum. He said, and i quote from one of his emails: " It is a little normal to have extra oil on the passenger side because that is where the oil separator ventilates and if you’re oil level is too high it exaggerates it. Sometimes this will make it a permanent issue but sometimes it will clear up"
Also, the Air/oil separator aparently is prone to fail and the part is at the 3rd revision now. There are some topics regarding this. If it was from Turbo seals, it would happen on both sides, not only on the right, where the AOS is also located. I will try to document the steps in replacing the AOS, for those who are interested.
On the stumble: fuel injectors? Pulled and examined? Cleaned? Years ago my wife’s 981CS had a terrible WOT stumble that was ultimately one or more badly varnished fuel injectors. One or more injectors with a poor spray pattern will cause poor low-load combustion and intermittently with symptoms one can feel from the driver’s seat.
i will add this to the check list. I did not do it on any of the cars, but also did not feel it was necessary, as the cars have relative low mileage.
I talked about this including with SamboTT who said to keep the oil level to medium. Not maximum. He said, and i quote from one of his emails: " It is a little normal to have extra oil on the passenger side because that is where the oil separator ventilates and if you’re oil level is too high it exaggerates it. Sometimes this will make it a permanent issue but sometimes it will clear up"
Ah. So, it is a issue with the breather system.
Also, the Air/oil separator aparently is prone to fail and the part is at the 3rd revision now. There are some topics regarding this.
Yup. I've see other's report on the AOS.
If it was from Turbo seals, it would happen on both sides, not only on the right, where the AOS is also located. I will try to document the steps in replacing the AOS, for those who are interested.
I wouldn't expect both Turbo seals to fail simultaneously. Regardless the AOS makes more sense and fits the data.
Originally Posted by Mufus
i will add this to the check list. I did not do it on any of the cars, but also did not feel it was necessary, as the cars have relative low mileage.
The issue with the wife's 981CS needed 6 weeks of diagnosis and many PIWIS logging runs. The injector replacement occurred only after many other possibilities were exhausted. At the time the 981 was two years old and had about 7,000 miles. Two possible explanations:
1) It was a launch vehicle that sat on the lot for ~8 months before my wife bought it (no new gasoline since factory, lots of start/stop cycles to move the car to different parking spaces, a few test drives, never getting fully warmed-up; thus perfect conditions for injector varnish.)
2) My wife had been using higher-octane fuel for track. I suspect the last tank - from a different source - might have been really old. And despite using fuel stabilizer the old race gas didn't play nicely with the injectors.
Note that in the US, almost all gasoline is 10% alcohol and the alcohol content accelerates the deterioration of the gasoline.
It seems like there were no such problems until Porsche quit using Mass Air Flow sensors. So, perhaps there is some variability in the pressure transmitters that are now being used.
Measuring mass air flow is Combustion 101. Surprising that Porsche would want to ditch such a basic concept.
It seems like there were no such problems until Porsche quit using Mass Air Flow sensors. So, perhaps there is some variability in the pressure transmitters that are now being used.
Measuring mass air flow is Combustion 101. Surprising that Porsche would want to ditch such a basic concept.
Most of the industry has moved from mass sensors to manifold pressure sensors for reliability reasons. Hot-wire and hot-film mass-air sensors have their own problems. Even in the best of circumstances they deteriorate with use. Apropros, an hour ago, I got off the phone with a client of mine, that with some long-distance text message help from me, was able to diagnose intermittent running problems on his Porsche. It turns out that a hot-wire mass air sensor I'd had rebuilt (as there are no new ones available for the model in question) failed in his car after about 2000 miles.
Problems like these have existed forever. They are just much, much harder to diagnose now because too much system behavior is implemented in software and there's almost no information available on what the software is supposed to do under various conditions.
I changed also the MAP sensors on both cars, as i suspected them going bad because of the repeated oil contamination. Not sure how senstive the actual sensor is, but i assume it must be in contact with air and not oil. It is driving me crazy allready. Because it happens on two cars, but times apart, and long after i modded them. So i cannot blame it on the tuning.
Totally hear you Mufus, would love to know what is causing this. Why does it clean up after 3000 rpm? Why doesn’t any code get thrown?? Why doesn’t anything look weird on a data log?
Im going to try and do some different data logs with brake boosting in each gear to see if I can get A longer log at the condition to look for anything.
Totally hear you Mufus, would love to know what is causing this. Why does it clean up after 3000 rpm? Why doesn’t any code get thrown?? Why doesn’t anything look weird on a data log?
Im going to try and do some different data logs with brake boosting in each gear to see if I can get A longer log at the condition to look for anything.
keep us posted with your findings. I received today the new AOS. I will try to install it this week. If the stumble is related, i will let you kow, but at least i hope i get rid of the oil on the passenger side intercooler hose.
A while ago I was wondering if the throttle position sensor or throttle by wire or throttle body butterfly control motor could be doing this??
If you drive along with or without boost and twitch your foot on the gas quickly it reproduces the same exact feeling. If any of these components had some sort of funky spot in them I could see it producing this. And I read about someone swapping throttle bodies for a larger one and having it “fix” the problem. Maybe it just got jarred into shape? Or maybe they got a new one with it?
i forgot that this was another thing I wanted to look into, just remembered on the ride home today.
A while ago I was wondering if the throttle position sensor or throttle by wire or throttle body butterfly control motor could be doing this??
If you drive along with or without boost and twitch your foot on the gas quickly it reproduces the same exact feeling. If any of these components had some sort of funky spot in them I could see it producing this. And I read about someone swapping throttle bodies for a larger one and having it “fix” the problem. Maybe it just got jarred into shape? Or maybe they got a new one with it?
i forgot that this was another thing I wanted to look into, just remembered on the ride home today.
I was thinking at this also, but coleague Duxi said the throttle body change did nothing.
Also, the swap with a bigger one is possible in the 9971 turbo. You change up to the GT3 thottle body, which has 83mm.
so, today i changed the AOS ( air oil separator ).
I did this, as i suspected to be the cause for the oil pool in the passenger side intercooler hose.
This oil build up, was being pushed up the intake system, all the way to the throttle body. This means , oil on the MAP sensor. Also today i found out that the car has anothe MAP sensor on the passenger side intake. Right in the middle. i never knew it, and never cleaned it.
Anyway, i took some photos with my phone and shared them with you to see what is going on in this part.
What i did noticed is one major difference between the part from factory and the new one. On the back, the factory one has a small nipple, ( not sure how to say otherwise ), with a hole in it. Like a small breather..? you can see it clearly in the photos.
The new part, still original from Porsche, but at the third revision, has this hole covered. i assume the ditched that breather..
Out of curiosity, i opened the old AOS to understand better how it works ( failed ), and to see what is inside.
Maybe someone with better knowledge of how this system works, can explain it better for us.
To reach this part i removed the following:
- rear bumper, rear wing , wing mechanism, airbox, y -pipe ( ipd ), throttle body ( which i cleaned , as it had some deposits. Not sure if those had some influence on how the car was running, but i cleaned it off ), pelnum ( ipd ), intercooler hoses, top and bottom ones.
- i also removed the ECU or DME , to gain better access to the AOS.
After i changed the AOS, i started fitting all back toghether. I cleaned all the parts from any oil residues, and inspected very carefully every part.
I did noticed something odd on the IPD plenum. this has one small hose in the back, with one vacuum valve. it was kinda loose, and the hose was dirty with oil. I added 2 clamps to keep everything thigh and installed the ipd plenum back in it's place.
checked all the vacuum lines and everything was fine.
As i suspected bad fuel in the fuel tank, i opened that also, and drained all the fuel out. It seemed clean and with no contamination of any kind. water, or other stuff.
Put new fuel in. OMV 100.
I also re-adapted the throttle body, erased all errors, and finished up the car.
In conclusion, the car runs great now. it seems more powerful, pulls very good from low rpm, and most important, no stumble of any kind. not even from the 7th gear at 60-65km/h. drops 2-3-4 gears and goes away, depending on the throttle input.
I cant say it is really gone, until i drive it for a few more days to observe how it behaves.. but i really hope it is gone.
I cant say that i found the solution. And that replacing the AOS is the key to the problem.
But all that i did today, led to a change on how the car is running. For now at least.
I will update you if anything changes. in better or worse.
If you have any questions, shoot.
old AOS - back old AOS - front old AOS - side old AOS old AOS new AOS - back new AOS - back new AOS - side old AOS - inside old AOS - inside old AOS - inside old AOS - inside baby
@Mufus you found and disassembled the check valve, on what appears to be the intake, of the air-oil separator. To *really* see what’s going on in that part, you need to cut it in half lengthwise, or otherwise expose it’s guts.
The AOS must have an inlet into which a foam of aerated oil flows. This foam comes from the engine crank case. The basic operation of AOS systems involve forcing the foam to undergo direction and/or velocity changes. Essentially: spin, turn and smash the foam against stuff. The important design-specific details are how, after separation, liquid oil flows back to the oil sump/reservoir and mostly-clean air flows back to the engine intake.
Since the crank case pressure and intake pressure varies from positive to negative (and not at the same time) an AOS system must have one or more check valves that prevent liquid oil or oil foam from being drawn into the intake.
Note that I use the term ‘system.’ You have one component of the system in your pictures. The system may or may not have more components scattered about.
I wanted to add a note / reminder.
In the past, several users had their DME's reset which resulted in the problem going away temporarily.
However, the problem always returned several daysl..
08-19-2019, 05:51 PM
