So my car has been going into limp mode recently in fifth and sixth gear. I started doing some research on the matter, with the most common thing being sticky VNTs. I decided to buy a bluetooth OBD adapter with torque to read the fault codes given by the ECU, and discovered that I was getting under boost, and occasionally not enough flow through the EGR valve. After reading through fabokas background material I decided I would get VCDS-lite and do some of my own logs to understand more of what was happening. 

 

The logs from group 11:

 

The logs from group 3:

 

 

Looking at some other logs I have found the actual boost seems like it is not following the specified boost closely enough. I can't hear any boost leaks, and I only get a slight puff of smoke when I put my foot right to the floor.

Can anyone shed any light on the matter? Or please could someone provide me with some logs from a normal functioning car?

 

Thanks, VapourXR 

Classic stuck VNT or mechanism.

Have you had a replacement turbo recently? Reason I ask is duty cycle at 4000 rpm is really low at 40%. Should be more like 65%. Which to me would explain why its not meeting request boost at around 2200 rpm.

 

Glad to see my info is helping people dig a little deeper into what is actually happening.

I've gathered all the stuff to carry out the VNT Mr muscle trick, however I don't really want to be doing it if it's not the problem. The only reason why I am not 100% convinced its the sticking vanes is that its not over boosting.

I bought the car earlier on in the year, and there is no history of a new turbo, which I expect means it the original as its a well maintained service history. That's what I was thinking too from looking at your previous comment on someones graph, and the actual boost followed the requested boost quite nicely. The graph was over a long period of time though so I couldn't really see the response time hence it would be nice to see a similar graph with WOT from 1500rpm to redline. Am I right in thinking the duty cycle is to do with the N75 valve? And if so maybe this could be faulty? 

 

Yes thank you faboka for taking the time to post tutorials etc!

When you did the log. Did you do WOT?

 

This is the first log I found. Its log from a XMAN VC hybrid on a stock map. The stock turbo hits requested a little sooner.

 

Yes, it was done with my foot to the floor in third gear from 1500rpm until almost the redline. I may do a few more tests when I get the chance as it felt extremely sluggish, and there was no sudden kick which I normally feel when driving the car. It makes sense looking at the logs I obtained from the run.

 

Cheers for the graph. I can't believe how flat the response of the turbo is in my logs! Do you know of a way to test the N75? 

Update on the situation:
I went to check the vacuum pipes/ test the N75 using vcds-lite this morning. Opened up the bonnet and found that the two vacuum pipes towards the very back of the engine back had completely melted and buckled, therefore no air could flow through the pipes. As i was replacing one of these pipes, I looked down to try and find what had caused them to melt and the EGR pipe between cooler and exhaust had split in two! Sourcing an EGR delete kit to fit on, and will replace any pipes that have melted. I can't believe the car has been running fine with only the odd "EGR flow insufficient" popping up. 

Will update again after EGR delete is fitted and pipes replaced to help anyone else in the future with similar problems.

Wow good find. You will certainly notice a difference.

Finally found some time and it's not been raining today so went to work on fixing the car. Hardest part was removing the EGR cooler. Turns out it already had a 'blanking plate' on the exhaust manifold, however it appeared to just be a DIY cut out of metal. Who ever had done it before did a shoddy job and there was no blanking plate on the EGR side of things. 

I replaced all the sections of leaking/melted vacuum pipes also and then started the car up. All I can say is wow! There is now all the power down low like it should be.

Only issue now is that I've done another boost log and this is the result:

 

My concern now is that the duty cycle goes well above the normal 60-80% and the turbo appears to be overboosting. With the EGR cooler out the way I had a little feel of the actuator and it felt smooth for about an inch of movement, so I can't see it being the sticky vanes. 

 

Could this be the ECU adjusting to fixing the issues? Just don't want the turbo to go now I've finally got it working!

Also the codes associated with melted vacuum lines were P0229 & P0401 for future reference.