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.

 

Here's the timing procedure for the 955 V8, I expect the 957 is the same.

I'm not an expert, but your theory on the chain tension sounds plausible. However if that were the case I would expect consistent misfires on all cylinders on that bank, and not just the one. Anyway, checking it would be the only way to be sure.
At 90000km it's unlikely that it's any type of "normal" wear, it would have to be due to some kind of "unusual event". As I understand it "chain stretching" is not actually "chain stretching", but wear between the teeth and rollers over time that increases the effective space between the rollers.
Possibly tensioner failure, but this should be pretty easy to see as the tensioner blade is a solid piece and any issues should be easy to see.

 

OK, hold on, on the timing chain. After looking at your fault codes, I remembered that the combination of misfire and fuel rich/lean fault codes are classic symptoms of a vacuum leak. You need to check all the inlet pipes (after the MAF sensors) for damage and also check if all the little vacuum pipes are there. It could be a small leak, which affects idle, but is negligible once airflow increases as revs increase.

 

Thank you for timing procedure. I will hold off for a couple weeks. I ordered a smoke machine to aid in checking for a leak. I disconnected the mafs and symptoms remained so that ruled those out. Will update when I have more info ...

 

Another thread mentioned the variocam vane adjusters use a diamond friction washer and sometimes at high rpm they can slip. Is this something that is possible or would i see all bank 1 cylinders with faults and misfires? I checked my battery and on cranking it dipped to 9.4v. I have heard 9.6v is the threshold so maybe my battery is the culprit? How can I check if #3 cyl is getting 12v to the coil pack... just probe it with a multimeter?
I attached a screen shot of when i drove with mafs disconnected. Fuel trims were off and misfire cyl 3 persisted only at idle but never when even slightly above idle. When i had to stop i held brake and just a 'hair' above idle so it wouldn't misfire. Also, with mafs disconnected durametric shows camshaft deviation fot both banks as '0'. Strange? Also, while driving my gear indicator on the instrument cluster just showed 'D' but no number for the gear i was in even when i selected manual mode. Stopped the vehicle, connected mafs, and presto ... gear display and camshaft deviation came back.

*** I keep reading +/- 6 degrees deviation is acceptable. Bank 1 is 9.3 degrees deviated and bank 2 is 3.2 degrees. If 9.3 degrees isn't enough to indicate a jumped timing tooth, is it enough for the cam/vane adjuster to have slipped???

Any ideas....?
Will update when I have more info ...

 

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Looks like it might be a two piece camshaft? You gotta go with what code your getting until you have ruled that out as a possibility.

Valve lift control fault to me would mean just that. Improper lift or timing on the one cylinder could most definitly cause misfires. I would say that slipping of the diamond coated washer is improbable. I have yet to see one verifiable instance of the vane controller or cam gear slipping on the camshaft. Impossible? No. Probable? I've seen or read nothing other than conjecture to indicate so.
You know, Durametric is only going to take you so far. If you re-time the cams you are supposed to replace all 4 diamond coated washers.
Why would you lose faith in Porsche quality? Everything mechanical breaks or malfunctions eventually, its the nature of the beast.

 

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. Anything 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 ...

 

Have you sorted out this issue yet ?

 

No. It's at an indepenedent Porsche garage being thoroughly looked over now. I will post the final solution on all forums I have posted for future owners with similar problems.

 

 

Multiple scored hydraulic lifters ... sticky at idle, but okay enough at any engine speed above idle with fewer misfires. Bought used heads to take the lifters I needed ... ran perfect once fixed. Have spare heads and sensors for sale now

 

Thanks for helpful information.
Did you replace anything for large camshaft deviation ?

 

The deviation threw the ecu for a loop so i dont believe the readings were valid when the lifter at idle wreaked havoc