You right it may be the boost control,change the selenoid as you said.

 

I did change the solenoid, now waiting to see if it happens again, next track day is not until November 14

 

May I ask what's the root cause finally?

 

Was there any update on this?

 

Well that was a waste of 3 pages. Any follow up???

 

I have just had a similar issue develop.
When driving at Sebring this weekend (yes, I stayed with 98 octane unleaded) my EVO GT 660 2001 TT would run fine showing 1.4 to 1.5 bars. Then suddenly I would loose boost to varying level, at worst all the way to 0.2 bars. I believe I could hear a wastegate stay open (the tone changes). If I ran really soft for a while, or stopped, the boost would come back.

No check engine light at any time. When I stopped I had P0491, P0171, and P0174 but I don't know when they came on as I did not check while driving.

Questions:
- Can a wastegate or actuator stick in this manner?
- Can the computer keep the wastegate open all the way down to 0.2 bars, possibly in response to MAF (Hitachi) faults?
- Any other ideas? - This is hard to duplicate on the road as I can not get the issue to occur other than on the track.

After changing to actuators from EVO when working on another issue we have recently cleaned and reinstalled the stock actuators (an actuator arm from EVO broke at a bend the first time out). This leads me to suspect sticking wastegate or actuator when it gets really hot.

I don't believe I have intake system leaks, anymore. In response to other CEL issues the engine was recently pulled and every hose and leak fixed, and the system pressure tested. This got rid of the CEL's finally. The real issue was a sticking check valve that gave P1109 errors at idle.

 

Sounds like the boost intervention safety feature motronic uses. IIRC boost intervention can be caused by lean mixture, excessive EGT or excessive knock activity. Our cars do not have EGT sensors, but they derive EGT from the O2 sensors. I would log fuel trims(short and long term), timing, EGT and knock sensors. Do you run solid motor mounts?

 

I run stiffer than normal, but not solid mounts.
If I read your response correctly the car can electronically reduce the boost all the way to 0.2 without giving errors. I thought the springs in the actuators kept more pressure on than that when working correctly, even without vacuum holding them shut.

 

I am not sure how your waste gates are adjusted. But the only reason the car runs an ECU controlled boost controller (N75) is so the ECU can pull boost before your engine grenades. Otherwise a simple and cheap MBC would have been implemented.

 

After changing to actuators from EVO when working on another issue we have recently cleaned and reinstalled the stock actuators (an actuator arm from EVO broke at a bend the first time out). This leads me to suspect sticking wastegate or actuator when it gets really hot.

I don't believe I have intake system leaks, anymore. In response to other CEL issues the engine was recently pulled and every hose and leak fixed, and the system pressure tested. This got rid of the CEL's finally. The real issue was a sticking check valve that gave P1109 errors at idle.[/QUOTE]

nothing at your engine, ecu or anything is able to reduce your boost to 0.2 bar.....

base boost is the lowest level.....

so if you dont have a big boost leak i am shure your wastegates are worn out....turbos are getting older and wastegates at this turbos are not the realy the best

remove your muffler check your waste gates ...of course it needs time...but i have seen many worn out wastgates with problems

 

Thank you.
Your response points me firmly at wastegates or wastegate actuators as boost goes below base boost and I have no leaks as boost goes back to 1.4 - 1.5 when the wastegate(s) close.

 

if a wastegatearm was broken, it is possible that the pin at the wastegate valve is broken. It is only a little pin but after that pin is broken you go into boostproblems after a while....

 

I agree this is likely the ECU cutting boost due to something it sees as dangerous. I've had a similar issue in my car going back several years that happens much more often in hot weather and/or on track days, and very rarely in cold weather. I've replaced most of the possible sources due to mileage/year (now 67k/'04) but none of them has made any difference.

I can't replicate it on cue and even on hot days my car will run just fine at the track for hours and then all of a sudden the problem shows up. I can almost always clear it up by restarting the car once or twice, but sometimes it takes more restarts or letting the car sit for 5 minutes to make it go away. It's been there now for probably 30k miles. It existed before I did my major build/mods, but only happened a few times. It definitely happens more now with the mods, but the fact it happened when the car was stock to me points to something simple like the MAF reading incorrectly.

Personally I believe it's related to the MAF since they're very sensitive and it's a part of the engine that can heat up and cool off very quickly, plus it sits right in the path of hot ambient air so it makes sense in hot weather it would happen more. If it was an O2 sensor or another similar one, then I'd expect it would occur about the same amount in colder weather since it takes a while for the exhaust and other parts of the engine to cool down, but the airbox/MAF area will change temps very quickly based on the ambient air temp.

 

Thank you. This answer is opposite to some of the prior ones. I am of the impression that the ECU holds the wastegates closed using vacuum, and can only release the vacuum, reverting the engine to base boost.

Can the ECU cut boost all the way to 0.2 bars?
What/how high is base boost?

 

Before you guys spend any more money chasing this problem, take off your muffler and check the CATS and make sure they aren't becoming unseated. The extra heat generated on track plays havoc with the welds, you get boost issues and there are no codes. I chased this problem for a long time and changed many parts until I found out it was the CATS.