I am experiencing stutter sometimes after hard acceleration (kick down). But If I floor it without kick down no problems. Then it charges pressure from 0.4-0.5. On kick down its at 0.6-0.8 depending on gear and rpm. My CTT is 2008 and has 180k km. Perfect service history and was taken care great by first owner. And now me also.

I have new coils, spark plugs,fuel filter (did all that before 10k km ,except spark plugs,before 20k km). Haven't tried other fuel. But I am constantly filling my Cayenne on one station here in Serbia,except when I go to business trips and holidays. But still the same problem. Maybe less but present.

What to look for?

 

You need to describe the behavior of the engine that you are experiencing a little bit better.

 

In my experience with a 955 CTT, stutter can be low octane (bad fuel) or coils/plugs. I believe stutter to be a result of pulling timing (due to pre-ignition of bad fuel) and/or intermittent weak spark (most likely due to a cracked coil issue).

Because you have a 957, I'd have thought you'd be more resistant to pre-ignition (and hence bad fuel) -- but I have no first hand experience with the 957. You might try running a new tank of [better] fuel or use an octane booster to see if you get a different result before looking elsewhere. In the US, some stations sell E85 (85% ethanol). In my experience, the CTT will run great with some extra E85 -- maybe 5 gallons out of a full 26 gallon tank. These engines seem love the extra octane. I don't run that way often, but every couple months I'll do it and the difference is immediately noticeable.

 

Basically what I have meant is that car on sudden occasions looses power and gets back up but that is happening very few times and briefly when I kick down. Its like 100% power,then stutters,pressure drops from turbo (I can see that on instrument cluster) then back up... But that doesn't happen when I push all the way down without kick down.

 

This is what I have found also when I was looking at the engine few mins ago... Is it alarming or not?

 

If you read carefully, I have changed coils and spark plugs. So I opt that out... We don't have that low octane fuel here in Serbia. Lowest is 95RON then 98RON and 100RON. I pour 95RON and 98RON. Havent noticed any difference in performance but the price difference from 95RON to 100RON is crazy. So 95RON and 98RON when traveling. And I do travel a lot with my cars. Although as I am rewinding in my head, maybe,just maybe those problem started when I changed fuel filter in tank. But it is not 100% true. Can't remember did I had any problems before. Also what do you think (and everyone else),should I notice some performance gain from 95RON to 100RON (even there is no word on 100RON in owners manual)?

 

Unfortunately, I wouldn't rule out plugs or coils just because they are relatively new. What parts did you use? There have been reports of poor outcomes with off branded coils.

Fuel spec for the Cayenne is minimum 98RON. From the manual "Your engine is designed to provide optimum performance and fuel economy using unleaded premium fuel with an octane rating of 98 RON (93 CLC or AKI).Porsche therefore recommends the use of these fuels in your vehicle."

As NoDoors has asked, can you better describe what you mean by "stutter under acceleration"? Does it feel like lots of tiny reductions in power? Or is your stutter bigger, and more intrusive -- like general rough running due possibly to fuel starvation?

 

I have purchased COSMO Racing coils and FR6NPP332 Bosch spark plugs. As for fuel. Check pic from my fuel doors. Also I feel a lots of tiny reduction in power. But... I have tested few scenarios today. Basically I have put stress in 3rd,4th and 5th gear under kick down. Today no stutter, but pressure builds up from around 2000rpm and after few seconds it drops from 0.8bar to 0.4-0.5bar. Diverter Valves?!

 

These are the coils I bought https://www.cosmoracing.com/high-pow...8-2010-4.8L-V8

And part number as you can see is 94860210412 (I think that -ICS is some sort or their branding)

 

I don't know what causes the low (.4 bar) boost condition. I've experienced it once or twice on my 955, but it's not been a chronic issue. I'll let others chime in with thoughts. I know the 957 has some key differences from the 955, so I'm probably not best to advise.

I'm assuming you don't have a Durametric or iCarScan or some other way to look for codes or engine log?

 

 

I know. I had that problem with evaporator hose that connects both separation (oil/air) units. Changed that hose and changed rubber membrane also. So No problems there. What to look else?

 

the Y pipe can develop cracks that goes into the throttle body. New one is ~80. Have you replaced all 6 of the charge pipe o-rings yet?

 

No I haven't changed those o-rings. Although I saw that connection from turbo to inter-cooler pipe is leaking on a seal. Left,not right. Is there some bundle for those 6 o-ring that I can buy all at once. And where are they all placed? Can I change that by myself? Also I saw some pin that goes arround the rubber hose that has metal end by the turbo? What parts I need to remove to be able to change that? I will check later the Y pipe and see if it has cracks or hissing noise. Also, not to forget, I can make YouTube video of my engine running and share with you guys. It is steady as like it is off. So nice idle.

I wanted to remove O2 sensors and clean them but I am unable to do so because my screws are so ridiculous. They are not thorex nor philips. They have only 4 inlets and thing in the middle. I haven't seen those kind of screws ever.

 

The fastener type you are describing is called a triple square.

Yes, you can change the O-rings yourself. There are numerous walkthroughs and videos that should help. It takes some time, but you can do it with simple tools if you are not well equipped. You will need 2 of each:

turbo to charge pipe
charge pipe to intercooler
intercooler to charge pipe that leads to Y-pipe
I would also get a new throttle body seal if you have never replaced it.

The old o-rings were black and the new ones are green. If a previous owner has recently replaced them, then they will be green. I am lazy right now, but you can find these part numbers and manual/diagrams from searching in my previous post about alternator replacement. As part of the alternator replacement procedure is to entirely remove the intake plumbing so that the radiator and front subframe of the car can slide forward for access.

The Y-pipe is very tough to tell if it is leaking due to the design. You will see what I mean when you pull it apart. It is quickest and easiest to buy a new one. Just get in the mindset that there is a lot of cheap (but expensive to purchase) plastic parts on this car that will need to be changed every 10 to 15 years. They get baked the hot underhood temps and become brittle after so many heat cycles. The O2 sensors are probably not your problem unless you are getting codes for them, in which case I would do them first.