Hey Guys - got a couple of issues with my 2008 CTT that I want to put to bed

1) The car has an intermittent stumble/roughness when accelerating from low RPMs (~2000) - once it gets to 2500+ RPMs the roughness is gone

2) I suspect I have an intermittent boost issue too (boost is inconsistent - sometimes it climbs to 0.8 and stays there, others it only claims to 0.6 and sometimes it will climb to 0.8, drop back to 0.5/0.6 and then climb to 0.8 again). The gauge numbers align with my seat of the pants feeling.

First of all - can someone clarify what I should be seeing on the boost gauge while doing a 3rd gear run?

Not sure if both of these problems could be linked?

I was sure #1 was coils and plugs so I changed them a few thousand miles ago for the latest greatest versions - made no difference - the stumble was still there.

Ive also ran a bottle of the Techron injector cleaner through the car and tried a couple of different brands of fuel, I believe the cleaner and different brand helped but the issue is still there

What is interesting is that the car drives smoother when it is cold - the hesitation is more noticeable when its up to full temperature

I have Durametric and can run logs if anyone knows which parameters I should look at to assist. I should also say that there are no engine codes when I scan with Durametric.

I`m planning to swap out the Diverter valves and N75 valve as first steps (cheap and easy) and contemplating whether to swap the MAP too as this eliminates any of these being the culprit

Thoughts? Thanks in advance!

 

Anyone?

 

I dont have a gen 2 but theres a lot of possibilities. First you have to rule out all the mechanical accesible stuff you can, because its the easiest thing to verify without codes to play on. I dont have a durametric so I dont know how they work but if you had an oscilliscope you could start checking waveforms of various sensors. You might also look @ the intake cam advance difference from bank to bank as datalogged. The gen 2 also has a different camshaft/variocam system than the first gen with the addition of variable lift? The root of your problem will not be realized with random guesses and parts swapping.

 

What condition are your intercoolers in? Have they been cleaned? Air filters?

Being that your issue exists below 2500K and not at full boost, makes this difficult to help solve. Something simple as a battery could cause similar issues.

-Does your tach bounce around at idle?
-When did this start?
-What service was made prior to issue?
-Is there a difference between in gear (driving under load) RPM vrs. park or neutral gear RPM?

 

Check your vacuum lines. Porsche really dropped the ball and used the cheapness plastic known to man for their vacuum lines and they are prone to cracking. There is a vacuum line at the very back more towards the passenger side that connects into a T that is very prone to breaking.

 

Yeah, that sounds like a good starting point, I did have a quick look at the what I believe is the correct T and it seemed fine but I couldnt be sure

Does anyone have an exploded diagram of the vacuum lines in a Cayenne so I don't miss any hoses or connections?

 

Check the 5:35 mark in the below video. The vacuum T I was having problems with is discussed at the 5:35 mark.

 

I've encountered a stumble/roughness in my 08 CTT around 1600 rpm. Dealer looked at this issue along with the Porsche Field Tech and determined that it is normal engine harmonics in the 4.8?? Since then, my crank sensor began failing (stalls, hard start, turbo overboost were some symptoms I felt when the sensor acts up. I'm waiting for shipment of new sensor. In the meantime, I hooked up my Durametric and monitored the crank sensor. I noticed that the pattern was very erratic even when the engine seemed to be performing properly. I am wondering if the new sensor might clean up the stumble/roughness at 1600 rpm. Fingers crossed.

 

Interesting.......

I'm gonna hook up Durametric and see what mine is doing out of curiosity

Perhaps you could update when the new sensor is fitted?

In my case if it is a sensor on its way out it is strange that it only is noticible at low RPMs, once its gets above 2000/2200 it runs strong.

It really feels like the classic coils/plugs symptoms that seem to plague Cayennes but in theory it can't be as they were the first thing I replaced

 

Use your durametric to have a look at your fuel trim numbers.

Lean numbers will indicate a possible vacuum leak.

 

I'm curious if we are chasing the same problem. This is a cut and paste off of another forum. Is this the same thing you're chasing Chief?

Trying to track down an issue I'm having on my 2013 TT. It has a stumble when accelerating in the 1800-2500 rpm range in basically any gear. If I punch it, it will sometimes act like a misfire.
I've changed plugs and coils and looked for vacuum leaks in the front and rear of the engine but didn't find anything.
I hooked up an Edge CTS to it and watched various parameters over the past few days but don't see anything obvious. Spark timing looks good and consistent, fuel pressure looks OK, Long term and short term fuel trims look OK (see below), and O2 sensors don't appear to be malfunctioning. Boost may be an issue as the CTS doesn't always read equal to the dash gauge (might be lag in time it samples the data). I checked hoses and don't see anything obvious and made sure clamps were tight.
I haven't checked under the intake manifold for anything yet.

So for data I never see the short or long terms get above +/-10%. Short terms go up when accelerating but then come back down to close to zero at cruising speeds or driving at a steady pace in the neighborhood. I've also sat at idle and revved to about 2500rpm with no load to watch them and once I hit a steady state they are almost always at or near 0%.

So back to the boost readings, I will see about 0.1-0.3 on the dash gauge and watching the CTS readout it will only go to 3 or 4 psi. Sometimes when showing 0.1 or 0.2 psi on the dash, it shows 0 or 1psi on the CTS. So just to be sure I think I'll check the wastegate diaphragms for leaks and then the diverter valves next. On full throttle I see about 8 or 9 psi, peak at 10 once or twice so I'm not sure how much it's supposed to be making. But I can't keep it punched for long due to where I live.

Any suggestions?

 

If fuel trims are OK, next check misfire counts.

 

How do I do that?

 

On the Durametric it will be under the "Actual Values" for the Engine. If you are using an OBD2 device, it will be under the Mode $06 monitors.

 

Without some type of log it's really just throwing darts hoping to hit something. It sounds like you're on the right path with plugs/coils then checking/cleaning injectors. If it's not on the spark side it has to be on the fueling side.

I come from a BMW N54, so these engines may be set up differently, but it has a LPFP and a HPFP and when this happens sometimes it's a sign the LPFP is failing as a high-load condition stresses it. Also, do these engines have a good PCV system or do the intake valves get gunked up like the N54? If gunked, they may need to be walnut blasted, but I haven't seen any posts about that here.