MM951

So after 225K wonderful miles I decided to figure out the misfire I've been getting on cylinder 6 whenever I exceed .4 bar boost. I installed all new OEM plugs and coils, the misfire persisted. I swapped the cylinder 5 and 6 injectors, replaced intake manifold seals, vac lines at back, replaced all the breather hoses, repaired some broken wires in other injector connectors and the car never ran better - but as soon as you pass .4 bar on the boost gauge...the datalogger shows constant misfires...on cylinder 6 I do hear a very light knock around 2K rpms but that has been present for over 100K miles...so for those of you that think your higher mileage turbos are immune to cylinder scoring...

I'll be replacing it with another, much against my finances wishes.

deilenberger

Please DO report it on the bore-scoring survey.. we're up to around 86 responses now..

https://rennlist.com/forums/cayenne-...03-2010-a.html

MM951

Done

deilenberger

Thanks!

MM951

Am I correct in assuming mine is the highest mile casualty? From my research, it seems my symptoms are pretty typical, no? Oh - and for those reading... I started burning oil at about 500-800 miles a quart.

oldskewel

Are you concluding that you have bore scoring? Just because other things did not fix it? Or do you have other direct measurements to get to that conclusion?

And really, if I had an engine that had any problem that had already lasted 100k miles so far, and the only real issue was a misfire at > 0.4 bar, I'd just keep it under 0.4 bar. My 2004 S does just fine with zero bar.

Good to hear of such a high mileage car there.

TomF

225k is a great run, IMHO! Sorry to hear about your misfortune, however.

Playing contrarian here for a moment in the spirit of keeping Don's survey data clean... Are you sure that it is cylinder scoring? Only a borescope will tell for sure and at 225k, it could be a number of things. If the scoring is advanced, a compression test will reveal that the cylinder is off by 20% or more, but even this is not definitive.

Cylinder scoring will present a knock at any RPM, even at idle and every engine that has had scoring has a knock at every rpm...A knock starting at 2k is not characteristic of the issue. Please post a video if you can, and let others chime in with their thoughts.

Cheers,
Tom

MM951

I looked at it with an endoscope - you can see the scoring, though compression is not much different from every other cylinder. Cylinders 2 and 6 were about 10% lower than the average of the other 6, though I never had any misfires on #2. The misfire on 6 is present at idle every now and then, it just always happens at any booster great than .4 bar. I've kept a light foot for the last couple oil changes I've noticed the misfire wasn't solved with plugs and coils. The injector swap and wiring repair were a hail mary of sorts..but I really miss WOT in the pig.

Just a thought I had...the scoring I'm seeing here is actually less severe than what I've found in my 951 when I pulled the head off almost 10 years and almost 200K miles ago, living before and after that headgasket at 18-22psi with a big aftermarket turbo etc...but the 951 really doesn't seem to suffer from oil consumption, any knocking or noise whatsoever.

Final random thought: I bought the car in SC with...130K ? It never saw cold weather until I brought it home in mid december. By March of following year I went from burning no oil to a quart every 1.5K to every 1K to now every 500-800 miles over the course of about 90K miles. The misfire under boost didn't show up until about 210K.

nodoors

Sorry to hear of your misfortune. Is your plan to keep driving it until things get worse, replace/rebuild the engine, or sell the car?

deilenberger

If it wasn't for the consistent misfire on #6 - I'd be looking at the AOS diaphragm.

This is a case where a "Ceratec" treatment might make for an interesting experiment... Amazon: http://a.co/d/4qHsnWR

It can't do any real harm to the engine at this point - and it would be interesting if it did any good..

MM951

My only option is to drive it until I can't, with the goal of fixing it. Call me spoiled, but the only car I'd be okay with replacing it with is another Cayenne Turbo..which I don't't think I could swing, and I've got lots of work into this one, all the problem areas addressed already.. some preemptively, some not! Though I wouldn't mind starting over with another 100-120K mile one if I could..

Hell, I'll try it. I'm not much of a mechanic (or machine shop) in a bottle, but I ordered 2 bottles. I'm 2,500 miles out from my next oil change. Should I add it now or wait?

TRINITONY

I would add asap just to see if it makes a difference.

deilenberger

I think I would also. If it's going to do anything useful you should see the results - at least some results - in 2500 miles. It supposedly does take some time to plate out on friction surfaces, but according to a few score victims, it did seem to help fairly quickly.

MM951

I'll let you guys know how it does. If I could go WOT again in this thing I'd be so pleased.

I also feel its fair to mention these cars hold up very well - the interior (minus seatbacks and a headliner i fixed) is like new at 225K and I have a big dog that gets free reign of the car. Besides the scratches and damage that comes with street parking in NY and being daily driven and a tiny bit of rust bubble coming up under the gas door, the car looks fantastic.

Mechanically, I did all the usual suspects, bypass valves, aos membrane, all the intake hoses (though I meant to do the y-pipe..always felt a bit laggy and that was the only part i never changed) , the under manifold coolant line (right after I did the pipes), then the coolant t's right after that..waterpump, coolant tank, drive belt...fuel pumps...plugs and coils a few times, repaired engine wiring a few times as i passed 200K miles, oh god the alternator.. that was terrible, the rear seat backs, headliners, bulbs, fluids, all the control arms, both front air springs, the level control module, the pcv valve itself and the vent line that goes down to the turbo, all the intercooler seals when the front end was off for the alternator...that's about it.

J'sWorld

Not bad for a 450HP tt 274 cubic inch v8!
Just remember that continuing to run the engine could add to the expense. 32 lifters times 30$ each, aluminum cam journals, variocam actuators/solenoids...... lots of area for FOD to work on.