Gentlemen,

For the last two years I have run the same custom tune from Todd Zuccone, and checked by Markski, providing maximum boost at 1.4 bars (turbos are K24's). I would even reach 1.4 bars at 10,000 feet altitude in Colorado but am now back at sea level.

Last spring maximum boost suddenly was 1.1 bars.Since I had major oil leaks to the turbos we rebuilt them and the recirc valves, and checked the intake for boost leaks using Markski's plugs. Maximum boost stayed at 1.1 bars. We have since disconnected the waste gate control hoses to check. Still maximum 1.1 bars.

Does anyone have ideas of what else could suddenly limit maximum boost?

TIA,
Ola

 

Does it feel like you have lost .3 BAR of boost? you should feel a difference like that. if not you may have an issue with the MAP sensor that is mounted i the y pipe just before the throttle body. They are cheap and easy to replace. 1.4 BAR is a lot of boost, do you have upgrade injectors? You said Marsky checked it so what ever you have it should be good.

 

Get a Durametric and a laptop to do some logs.

 

Thank you, both, for your quick replies.

Responses to the two responses received:
- I have run Durametrics. The logs show very similar values between 2 years ago and now, with the exception of the lower boost. Also, acceleration from 3,000 - 6,600 rpm is appr .7s slower in third Tiptronic gear.
- I do feel the difference.
- Don't know what MAP sensor does, or if it can change max. boost. Can you explain?

Will check waste gates for proper operation next on the advice of Markski.

 

The Manifold Absolute Pressure sensor is what provides the pressure reading for the boost readout. If it was reading wrong the logs would be wrong also. But you said you can feel it so it is probably not just a bad sensor.

 

Based on my experience with my 996 Turbo in Wyoming at around 9K feet above sea level the behavior is normal. The bulk of my driving was at or very near sea level. As a result the highest boost I ever saw with my Turbo was 0.7 bar and even to see this required I pay attention to the conditions. Otherwise all I would see would be 0.6 bar.

When I talked to the Porsche techs about this I was told the engine controller will only allow as much boost as is necessary to satisfy the torque demanded by the driver via the e-Gas.

So when I found myself in Wyoming at in some cases nearly 9K feet above sea level and when I followed the same procedure at that higher elevation as I did at near sea level my Turbo manifested 0.7 bar "easily" and even manifested 0.8 bar and even 0.9 bar. This was the engine controller allowing for more boost to satisfy the torque I was demanding. Might add the higher boost values were not glitches but were present for a good while and legitimate boost values. Might add the Turbo accelerated like a scalded cat even at altitude due in no small part to the additional boost.

(This sort of agrees with my experience with my VW Golf TDi. I was a bit concerned about taking it into the mountains what with only 90hp on tap from a 1.9l direct injection turbo charged diesel engine but the engine surprised me and was hardly fazed at all by operating even at the highest passes on I-70 in Colorado. The "secret" was the ungodly amount of boost the turbo was allowed to make, and necessary to satisfy the torque demanded.)

In short you are seeing 1.1 bar boost now that you are at sea level. At sea level with the higher air pressure and oxygen content the engine controller only needs 1.1 bar of boost to satisfy the torque demand.

 

I think there's something wrong for sure. Maybe a a bad N75 valve? How is your fuel quality? I am on 91 octane and limited to 1.2 bar. 1.4 is quite a bit.

 

you did a boost leak test......and does your system hold the pressure at about 1,8 bar ?

after rebuild your turbos do you renew your wastegates to oem wastgates? (with Oem wastegates only 1,1 bar max can reached. / 1,4 bar at minium you must have 0,8 bar or 1 bar wastegates)