My Cayenne has been stumbling (almost like a vague misfire) for a little while and I think its getting progressively worse

I changed the coils and plugs recently as a first step (all new parts, latest version of the coils) but it didn't help

I`d swear the issue is not so noticeable when the vehicle is cold and creeps in as it warms up.

I used to just notice the smallest stumble when accelerating from low RPM (classic coils I thought hence why I changed them) but lately I also notice it when accelerating hard even in the 3000 - 4000 RPM range, no real pattern except that it`ll lose power ever so slightly for just a split second and feels like a misfire

I`ve scanned it with Durametric and there are no relevant fault codes

Any ideas? I read on Pelicans tech guides that dirty injectors can cause these type of symptoms (stumbling etc) - any way to verify (check values on Durametric or something)?

I know the fuel pumps and high pressure pumps on these cars can be problematic so would these symptoms be indicative of either of these failing?

Any help would be greatly appreciated

 

Anyone know what fuse needs removed to make the car default on to the second fuel pump?

I figure I may as well try this to eliminate something

 

I had very similar symptoms with my 04tt, even noticing it was not nearly as bad when cold. When warm the performance was underwhelming with noticeable stumbling on moderate acceleration.
I replaced plugs and coils, as well as the torque arm since it was seriously deteriorated, and all is well now. I'm talking night and day difference.

 

Just solved my problem which was a simillar to yours. Did the same and changed the same. Coils, plugs + air filter and MAF. Still the same.
I showed the OBD readings to a friend and he told me very straight looks like a air leak problem.

fuel trims not ok
air stream not ok
i disconnected and checked a lot. No found.

yesterday by accident i saw a very small tube hanging arround close to the firewall behind the intake manifold. Found the other end, connected both and voila. It works. There are a lot of such lines and hoses. If the car has some years they get briggle or they may disconnected by accident while working in this area. Go and check visual.

 

I replaced exactly the same parts as you (plugs, coils and torque arm) but if anything my symptoms have kept getting worse

 

When you say OBD readings what do you mean?

If you`re referring to Durametric scans mine come back clean (at least the engine scans do)

 

Has anyone who's had symptoms successfully used an injector cleaner. Pelican has a tech article on dirty injectors that describes symptoms very similar to what I am experiencing

If so I`m looking for recommendations (bear in mind I`m in Canada so our choices may be different)

 

Sniffer - just give us a small clue. What year/model Cayenne are we guessing on?

 

2008 Cayenne Turbo (957)

 

with reading i mean with my icarsoft i can have a life reading when the engine is running. I saw the fuel trims and the air stream numbers and a pro in the forum tend me to a vacuum leak.

codes i had only sometimes.

Lean running

i guess its not neccessary the system is storing codes beacause of this fault

 

I understand

Were your symptoms noticeable even under a steady throttle? Mine are really only noticeable under acceleration

 

yes something like this. When crusing with a low steady rpm it was almost ok. But any change in throttle position feels very bad and no power at all.

 

That makes a difference. I'm not an expert on 958 Turbos, but I do recall reading about one or two plastic pipes that can break due to brittle plastic that effect performance. Perhaps someone who has experienced this can jump in and point you where to look..

 

Oh - for a fuel system cleaner - Techron is pretty much the gold standard. I imagine it's available in the great white north.

 

Mine is the gen 2 957 but I *think* they both use the same 4.8 direct injection engine anyways?