NewToPig

So my beautiful 957TT super optioned that I paid off last year... puffed white smoke at the alignment shop. I drove it home and it was spitting and popping on decel. Overdue for coil packs and a lot of just small things. Ordered 2k of parts between Rock Auto, ECS, and Pelican. Starting doing coil packs, replacinging the AOS and get the Cyl 8 plug out (of course last....) and it is covered in soot/oil. Did a compression test on 8 and the one in front of it (6 or 7?) and 60 psi on 8, 220 or something in front of it. Said some cuss words and closed the hood.

That was about 2 weeks ago. I just had to walk away from it. I will scope it but I assume I know what it is..... I am rather disgusted in this superior engineering. Sounds like 08 was a bad first year for 4.8 as well??? 115k miles.

Soooo my friends, once I scope it its either a really cheap roller, 4.8 engine swap (looks like $5k), or send to flat6 and invest in this thing for the long term.

For those that we have resleeved, what did it cost?

At this point rolling it off a hill and getting a cheap VR6 motored 955 sounds like the only thing I can tolerate. And I say that haivng 3 Cayennes so far.

Thanks!

brett968

Sorry to hear that. I'm guessing you are assuming the problem is cylinder scoring? That may (or may not) be a premature assumption. Did the engine exhibit any symptoms of cylinder scoring before this latest event? Specifically, did you ever hear anything that sounded like piston slap? If these symptoms were never there then it is quite possible something else happened. If you are lucky then the problems may be isolated to the top-end, in which case the repair bill could be considerably less than a full rebuild, albeit still not cheap by any means. I lost the original engine in my 4.5 S due to a cracked spark plug insulator which led to a bent valve and loss of compression on cylinder 5. This was at 270k miles. I was overdue for spark plugs by 5-10k miles. In my case, the problem cylinder had no compression whatsoever. Since the engine had so many miles, it made little sense to just fix the top end so I went with a long-block that LN Engineering had on clearance. These long-blocks aren't available anymore unfortunately. Based on previous discussions here, if you assemble the engine yourself and do the engine R&R, you are probably looking at $12-13k to go through everything properly, and $15-18k or even more if you have someone else do the work.

I would suggest performing a leak down test and trying to isolate whether air is leaking past the rings, intake, or exhaust. I'm assuming you've checked the oil for coolant cross-contamination.

Don't bother with a junk yard engine. BTDT, but that's another story.

NewToPig

Thanks, The only only failure mode I can imagine for low compression AND oil would be the headgasket. Just low compression could be valves. I suppose a cracked head could do it. At $15k, I'd rather just sell the chassis and finish my 64 Gladiator or get another 928. They are nice trucks and my first Porsche but just too risky. When I bought it the cylinder score issue was known but thought to be much more limited to 955 S.

I will post photos once I find my scope. For clarity, the issue started out of no where and has about 15 miles on it since noticed. The engine sounds fine. The exhaust crackles and puffs at start up (mimicking a failed coil and AOS). The second cat delete and techart muffler accentuates the sound.

Many thanks.

cordsig79

Sounds like a head gasket to lose pressure, I have gone through 2

BrianC72gt

From the wishful thinking drawer I hope for the following: Failed PCV resulting in huge amounts of blow-by coking up the heads preventing the valves from fully seating at cranking speeds but fully closing in the presence of combustion pressure. I pulled the heads of my dearly departed 2000 D2 A8 after a routine timing belt change somewhere around 150K miles thinking I had a whoops with alignment marks and valve damage. Low compression on cranking from a couple of cylinders. No damage, but the heads were black with carbon deposits so heavy that some of the valves were not fully seating. Cleaned them up, and replaced the PCV, clean as a whistle thereafter.

Also, does the 957 accumulate oil in the driver side lower intercooler elbow like the 955? Got my 955 almost 3 years ago and it started smoking in a few months, freaked out, then drained the elbow - solved. Drain it at every oil change and that's a non-issue. You can get replacement diaphragm & spring to do a low budget PCV rebuild.

Rather than a compression test, you could also do a leakdown test, bring the questionable cylinder to TDC, pressurize it, and listen for the cause of your compression loss, slowly turn the crank on power stroke to listen for scoring or bore wear. You can also remove the intake manifold and have a look? Worth a shot?

dr914

I agree headgasket. I would start by leaking it down Please do not assume the worst!!

NewToPig

Thanks for the encouragement cordsig79 and dr914. I have a leak down tester and can see where the air goes. Sticking the camera in there too will help. Its just been one thing after another on this one lately. I would much rather pull the motor to do mounts and then headgaskets etc instead of rebuilding the motor.

Thank you for opening that drawer BrianC72gt - I would like to see what is in there haha. SOOO its seems there is no replacement diaphram for the 957T AOS. I ordered the poplar one but its a little different. I think I have to buy the whole driver side assembly. That was my first puff of smoke thought (also common on 986).

Will report back and thank you for the optimism!

TomF

There is definitely an aftermarket 957 AOS diaphragm out there somewhere. I remember looking at one on a European company's website many years ago when I was dealing with my 2008 CTT issues, eventually leading to a diagnosis of bore scoring. Let me do some more digging and see if I can come up with it.

TomF

Here's the old thread with the info I was referring to. https://rennlist.com/forums/cayenne-...ement-diy.html

Libast

http://www.klaindustries.net/


Here's a US based provider of them too

Petza914

From what I've read, I'm not sure the separately sold AOS diaphragm fits correctly and you really need to but the complete valve cover with it integrated in. I wouldn't do that until you find the source of the compression issue.

08 has a higher incidence of scoring failure than the next couple years, possibly because the cylinder honing process was changed for 09.

Fingwrs crossed for you.

TomF

There it is! Thanks for posting.

J'sWorld

Thats crazy.

J'sWorld

Carl @ 928 motorsports is your best option.

TomF

+1 <THIS>