I am driving a CTS which has got its turbo tuned to boost 1 bar of boost.I drove it the other day at a constant speed of 220 kmh with full boost.After some time i realised that the boost had dropped to 0.4bar and could not increased anymore for the rest of my remaining distance.
The car was parked with engine off for an hour,after i restarted it again,the boost problem was gone,so i wonder if it was because that the turbos were running at too high a temp. that the boost was being reduce to prevent damage or what.I hope some one here can advice,many thanks!

PS. Till now i am unable to reply to post which i dont know why,so i will thank all in advance and mod pls activate my reply capability as i would like to share my experience on the make.Tks!

 

Heat soak.

 

Or if it is lurching, could be a coil pack going out. Had a friend with that problem, but he would get a blinking check engine light and then it would go out.

 

Coil packs, just happened to mine....

 

hope u got it fixed

 

I realize this is an old post, but wanted to comment and question.

I purchased a used 05 Techart Magnum CTS. I immediately noticed boost was only .4 bar, accompanied by what clearly sounded like a big boost leak. I replaced both DV's and now have .8 bar for the first 30 seconds of hard driving, then it drops to .4 bar. Cycling the key restores boost.

Next, I removed the vacuum line to the wastegates. Boost no longer drops off to .4 regarless of the length of the drive -- but there is no spike, no ability to go beyond .8 bar. Now, trust me, I am not trying to get the boost higher and damage the engine. It's just a diagnostic observation. If the car was operating normally, boost would surely continue to climb without wastegate regulation. Car has full techart exhaust. Either not developing proper power, or restriction in the remaining cats (bypass pipes ordered).

So, in the 'coil is bad theory' the computer must be detecting the misfire and placing the ECU into a 'limp' mode by reducing boost. Removing the ECU control of the WG's takes away its ability to reduce boost under these conditions.

No CEL of any type under these conditions. Dealer is last resort for me. I would rather buy a set of 8 coils and give it a try.

Ideas? I'll continue to post my results.

 

need bigger turbo fans.

 

Do you have any idea as to where the DVs are located??? I cant seem to locate it on top of the engine.

 

The diverter valves are not accessible from above.

Passenger side: (the 'easy' one). Remove the passenger wheel well liner using a torx bit. Not all screws must be removed -- just the front dozen or so. It will be easily acessible at this point, and there is good access to get two hands in there.

Driver's side: This is the difficult one. I would first remove the under tray (same on used to access the oil filter). This is h*ll on my techart package since the undertray is fiberglass and covers much of the area in question. Next, I would remove the intercooler hose that is directly blocking your path to the dv close to the driver's side wheel. If you have ANY doubt that you may drop something in this hose, place a clean rag in the end while it is removed. Don't forget to remove the rag when done! You will need the longest needle nose pliers you can find. Go shopping for a set before you start, or you are in for a frustrating experience. You may find you can get a second hand in better if you also remove the wheel well liner. It will take some patience to slide back both spring hose clamps. Don't let them snap back once you have a good hold on them. They are likely to spin to an angle that you cannot access with the pliers when they 'land'. When you get a good hold, remain comitted to getting them off in one action. Bear the pain and go for it. You'll need some gloves if you don't like bleeding. Really -- it's tight up there. Do this on a cold car, or the experience will be extra miserable.

If you have good luck and patience, you should be able to change both in about 1-2 hours.

I bypassed one of mine for the moment, and installed a Turbo XS blowoff valve on the passenger side. I love the sound, and the MAF loop does not seem to be complaining too much. I release throttle and tap upshift for every gear and get fantastic blowoff. I'm tempted to install a pair instead of my EVOMS DV's that are ordered to arrive today.

Still need to find what I believe is a big boost leak. Have various blockoff caps and a set of tire valve stems to pressurize and test the system. I'll post which sizes fit the best for each end. I plan to cap at the Y pipe and at the air filter and test right and left banks independently.

 

THanks for your guide! Just wondering the wheels must be removed in order to access the wheel liner I assume.

I also heard from a Porsche tech that the driver side DV can be access by removing the intake box. Do you think its possible? Right now there is so many things on the car such that I cannot access it unless I use a lift. Did you happen to use a lift as well?

Any other tips is also appreciated!

TIA!

 

Sounds like something definitely needed when doing an ecu flash

 

The wheel liners may be removed with the wheels in place. Just set the suspension for maximum height. This can be done on the ground, but of course is easier with a lift (I've done it both ways).

I would recommend installing EVOMS intake and DV's at the same time, as you are correct about the increased access with the intake box removed. I find one hose is easier to remove from below, then you can remove the intake tube from the turbo (one hose clamp from above) and lift the tube with DV attached. Now, swap the DV while outside the vehicle, lower the tube back in place, then reconnect the lower hose from below. You are at this point doing 90% of the labor involved to install intake -- so just go for it! Everything is easier to acess in the engine bay with those bulky airboxes missing, too!

 

Thanks again sevenspeed! Just did my install! Took me around 3 hrs without the long needle pliers.

 

I just got the same "half" boost problem today. Sometimes boost is just 0.4bar under full throttle. I closed throttle and floored the engine again and full boost was back (0.9bar on my 2005 Cayenne Turbo S). I didn`t have to restart the engine. Also there are no fault codes. I already changed diverter valves but the problem is still there - sometimes. Any idea? Maybe a damaged boost solenoid valve? Car has about 100.000 miles done yet. It´s very cold outside here in germany...should be no heatsoaking problem.