2008 Cayenne GTS MIND BOGGLING ENGINE LIGHT ... BEGGING FOR HELP

[oatmealadam]

I am praying anyone with some expert knowledge or past experience can help me with my valve lift control fault codes and misfires all on bank 1. Please see the 5 attached pictures from my Durametric. Vehicle is a 2008 Cayenne GTS with 90,000 kilometers. 4.8L V8, automatic.

Several months ago I got a CEL coming off the highway from about 135kmh to a stop. At that moment the CEL illuminated and the idle became rough and felt too low. Get home with full power and code only shows valve lift control fault on bank 1. Read through forums and common fixes … thus far I have replaced several parts as I will briefly elaborate below:

All 8 coil packs & plugs, valve lift control solenoids on both banks, cleaned MAF’s, changed air filters, all 8 fuel injectors, cleaned backside of intake valves, cleaned air intake and throttle body (re-calibrated throttle position), disconnected battery for hard reset of modules to re-learn, swapped camshaft position sensors between banks. I swapped coils/plugs as well to see if the problem would follow, but it only affects bank 1. Valve lift control solenoids and fuel injectors are the newest part revisions.

I did a compression test, leak down, and borescope. I had a master Porsche mechanic at an independent shop verify my numbers are all similar and within reason. Nothing out of the ordinary. One strange after effect from cleaning the intake and after swapping injectors for new ones was the rough idle was at that time much smoother and stable, BUT when I took it for a drive at about 3500 RPM it felt like the engine was being held back and the RPM’s wouldn’t increase as rapidly as it did when the idle was rough. So it was evidenced to have smoother low end idle, but almost like a loss in top end power … maybe variocam wasn’t active??? After the engine cooled overnight and I drove it the next day the rough idle returned, BUT I once again had rapid RPM increase at higher RPM and full top end power … the exact opposite of the day before. This phenomenon was replicated three times. The first time was after spraying CRC intake valve cleaner into the running engine. The second time was after doing the compression and leak down tests (plugs removed of course and turning clockwise at the crank). Third time as mentioned above. However, after each time it’s the same scenario, let the engine cool overnight and rough idle as usual next day with full top end power. This is how it is at the moment.

I have read forums for hours, visited a Porsche Premier dealership, and been to a master Porsche tech shop. The dealer wasn’t too investigative for my liking and their diagnostics are very expensive. The independent shop is thinking it may be a timing issue and wants to reset timing. My Durametric pictures show the cylinder banks are off by about 6 degrees compared to one another. The indy also recommended the fuel injectors judging by the fuel trim values, which are in all honesty a bit better now because they were double digits previously.

SORRY THIS IS SO LONG, BUT BELOW IS THE POINT OF MY POST NOW.
I have the fault codes shown in my attachments. The software incompatibility with transmission control module fault is a new strange one that only came up after the 2nd and 3rd time of having top end power loss with MAF fault codes … like it was suffocating for more air, but shifted rough in anticipation of a rapid RPM climb. At the moment the transmission is both auto and manual sport shifts fine.

When idling rough, cylinder #3 misfires constantly. In a span of several seconds it has misfired in the double digits. HOWEVER, as soon as I drive, whether easy or hard acceleration, the misfires are gone. The misfires only return when nearing a stop (<10kmh) or when stopped at idle in park or drive. My fuel economy is still giving me about 500km out of a 90L fill up … so I think that’s typical.

Being that I have replaced some common parts for this problem here is my theory I hope someone with in depth knowledge can confirm may hold true or is completely off and impossible. Perhaps rare, but is it plausible coming down from a high speed run off the highway that my timing chain could have jumped a tooth or teeth? Is 6 degrees variance between camshafts tolerable? How many degrees is 1 tooth on a cam gear? Being the chain is 1 piece, the tensioner is only on bank 1 side, is it possible the tensioner has failed and allowed slack on bank 1 to jump a tooth and change timing? Is it possible the chain is stretched at 90,000km?

I bought the timing tool kit and have a rough idea of how to do it. I would turn the engine by hand after the job to ensure the valves clear the pistons. If I am unsure I will just tow it to the indy. Does anyone have a timing procedure or link to a write up for the V8?

I appreciate everyone’s input. I am frustrated and tired of throwing expensive parts at this problem. I am waiting for my timing tools to arrive. This is my last resort. Beyond a timing issue I am clueless. If it is timing, I am not sure why cylinder 3 is most affected. Sometimes cylinder 2 gets an occasional misfire, but nothing near as frequent as cylinder 3. The other cylinders must be firing fine, but valve control faults may be due to not seating correctly with TDC due to timing??? My thinking as that the misfire ceases at anything above idle because the timing chain now has a bit of tension applied to take up slack or advance timing? Is this why I have excellent top end power range and able to cruise along through the city without misfires until I slow or stop???

Thank you for your help and hopefully someone can solve this puzzle who may have gone through what I would like to believe is an extremely rare occurrence before I lose all faith in Porsche quality.

***If you need me to grab any live data from Durametric for pictures to verify something let me know.

[manbridge 74]

Tough nut to crack for sure. First, kudos for all the hard work spent. Second, I mostly work on air cooleds but have R&Rd an 08 GTS 4.8 due to spalling on Lokasil cylinder liners. So I'll give it my best from what we've experienced.

I believe you are on the right track as the cam phasers on these are known to get debris in them and cause issues. There is a small filter screen on early 4.8s that was removed later in production and it's common practice for our gold level tech to get rid of them if he's in there for other issues.

[oatmealadam]

Thank you for the reply. What exactly do you mean by the cam phasers? Are you talking about the screens on the electrical solenoids on each bank near cylinders 1 and 5 that change oil flow into the mechanical variocam gear on the front of each intake camshaft? Or are you speaking of the actual mechanical gear on the front of each intake camshaft? Or am I way off and it's something else?

How would I verify a failing timing chain tensioner? It's just a spring isn't it? In my timing tool kit there is a pneumatic tensioner to apply constant tension while setting the timing. Would it be plausible to install this pneumatic tension with my air compressor, run the engine to see if it smooths idle??? If it's smooth would that show the tensioner has failed and explain why under some throttle load above idle speed the misfired cease and the engine smooths?

Thanks

[manbridge 74]

Phasers are what camshaft actuators were first called by other manufacturers so I still use the term. I believe Porsche calls them cam adjusters. But yes they usually have a screen as well and will cause problems like you're seeing.

I am away from work this week but will try and supply you the most accurate info come next Monday when I'm back at it.

[manbridge 74]

Also, I don't think you've jumped time as that will cause an almost instant CEL.

[oatmealadam]

UPDATE - I did a load test under the bonnet and the load tester needle was on the better end of nearing "weak" indicator. So, the battery is far from terrible. Also, just for comparison I load tested my Touareg TDI the same way and got an almost identical result and my VW has no issues. I didn't have time to pull the seat back to test off the battery directly, but would my result differ straight off the battery terminals compared to the engine compartment connections?

Secondly, I tested ALL 8 plug connectors for the coil packs with the ignition turned "on". All 8 connectors gave me a 12.17V reading ... so this would mean they are getting power and have continuity. Oddly enough, with the Xenon headlamps running and ignition turned to the "on" position, after I went to start the engine I got a PSM failure flash on the instrument panel. Shut the engine off. Started again and it was gone. Is this one of those unexplainable faults as people mention with a bad battery or low voltage after I had been draining the battery while I ran diagnostics?

Lastly, I used a fog machine fitted with some tubing to direct the fog into my intake manifold. Thinking a vacuum leak may be possible. I checked all over the sides, rear, and intake area, but no smoke came out anywhere. However, I am not sure if the party fog machine has sufficient pressure to force fog out of potential leaks. Thus, I am not saying I would rule this out, but preliminary tests indicated no leaks.

I did this fog test because my misfire on cylinder 3 only occurs at idle and not driving. What I do now is drive normally, fast and slow, but when I see an unavoidable stop coming I begin to left foot brake and just as I stop I am already using my right foot to raise the RPM to around 1000RPM. Anythign over idle, even 1000RPM, stops the misfire and the engine runs smooth. ??????????????????

Can anyone tell me how to definitely rule out the variocam adjusters attached to the front of each intake camshaft? Sometimes they're referred to as vane adjuster, cam phasers ... these are mechanical gears that are fed oil from the electronic solenoids.

Lastly, does anyone know where I can get a DME re-flash? Is it a dealer only service and what would it cost? Does it need to be removed from the vehicle or can it be doen via the diagnostic plug for OBD II ?

Thanks for any input. Something is better than nothing and even something you may think is common sense or irrelevant may very well prove to be valid. Keep the replies coming ...

[MPOWDER]

Did you ever find out what the issue was as I have the same problem. Car runs fine but that pesky CEL Light will not go off. Did all the things you did.

[oatmealadam]

Originally Posted by MPOWDER

Did you ever find out what the issue was as I have the same problem. Car runs fine but that pesky CEL Light will not go off. Did all the things you did.

Yes, I did. I was a sticky hydraulic lifter. Bad at idle, not so bad driving with increased RPM and oil pressure. Bought 2 used heads and rebuilt top end. Other lifters showed signs of soon to be failure. A VERY costly repair and a terribly engineered design of the oil orifice on the lifters practically promotes dry start ups and lifter bore scoring. Had the orifice been on the top against gravity oil could sit there waiting for next start up.

It is very expensive to diagnose with certainty because you need to remove the heads and have parts ready.

My advice, if you exhausted all my options, this could be the same issue. Either drive it until it is undriveable OR repair it slowly after locating used, but good parts.

I sold mine after repair and accepted my losses, but did enjoy it for the time I had it. However, never again will I buy. Porsche after dealing with Porsche Canada.