Cayenne Turbo, underboost and overboost :( - Page 1 - Porsche General - PistonHeads UK

Hey Guys, wonder if someone can offer me some advice, or if anyone has seen this before. I recently bought a late 2004 Cayenne Turbo (955) which I think is great. Less than two weeks ago, it started to only run at 0.4 bar of boost. it would be fine when it was started, but once warm, when the engine was loaded, it would hesitate slightly, then from there, only run half boost, until restarted, and the problem would happen all over again. I put it into my local porsche dealer, who ran it for codes, where it came up with P0299, Turbo Charger underboost. The dealer said my N/S intercooler was burst, and along with a few other little bit and bobs, charged me a small fortune for replacing it. The problem is still remaining, and now I have my own code reader, under futher investigation, I've found it has codes P0299 Underboost, P0234 Overboost and P0441, fuel system evaporation valve faulty. I dont think the latter is anything to do with the problem, but you never know. I think the problem is caused by a vacuum leak, in the area's of the turbos or the recirculating dump valve which may have a split in the diaphragm?? it's a bit funny however, how the problem is instantly reset, once the car is turned off and on, which may point me towards an sensor problem, unless the dump valve and actuator are not just mechanical. Does anyone know how best to get to view the actuator on the turbo, or the dump valve? Is it best to get into check them from underneith the car? it's a rather busy, packed engine bay. Has anyone come across this problem before? or have any idea's of anything else to check?? Thanks in advance ..... Chris Edited by gasguzzlingV8 on Monday 27th June 22:41

Hi the last time i had po299 fault,it was the "Y" section at the throttle housing opening up around the seams when flooring it in 3rd gear. Chris

Wombling free....

Hi Ahhh, replaced the Y piece in a attempt to find the problem but it's still occuring. It's when the engine is under full load, just before it comes on boost, that is the point which it decides if it to run at 0.8bar or only 0.4 bar Its doing my head in Anyone want a nice Cayenne Turbo??

Hi, It could be a number of things with Cayenne Turbo's. The breather system can cause real problems as it ages and perishes. Would need to be looked at by someone who knows the Cayenne model range well. We would look at it if you are struggling. Mike

Where you based Mike? This wouldn't be anything to do with the fuel evap soilnoid would it?? Chris

IIRC from my time owning a 2003 Turbo 0.4 bar is limp home mode. By restarting the car you have efectively put the car back to normal mode untill you bring it on load. do you remember what your max boost was reading on the gauge. My turbo was brought up to the Turbo S spec,then I had a Revo Technic stage 2 Turbo system fitted. The power was just short of 600 bhp. The OPC immediately found out I had it modded by the over boost code. I was running 1.1 bar. So is there any chance yours has been modded and haven't been told about it. ie overboosting, then going into limp ( under boost) .....just a wee thought.

It's running 0.8 bar on full boost. I think it's standard, it's not fast enough to be modified. It's falling into limp home mode, just before I come on boost at 3000 rpm (approx) normally in 3rd gear. I'd like to keep it and maybe increase it's power, but I need to find out what is causing this underboost. Thanks Chris

Have you changed the boost control solenoid? They can go faulty on the 993 turbo and not show a fault code, may be the same on yours. Worth a try..... Also worth checking that your actuators are working properly

Hi gasguzzlingV8 Iknow this post is old but did you ever get to the bottom of this issue ? I am currently having the same issues