... I swapped out some vacuum lines last night. I replaced bpv to the bpv control solenoid line, bpv control solenoid to intake manifold line and intake manifold to fpr line.

I put the GIAC chip back in today and did the tba and went for a long drive. I had the code thrown again so I thought about what I had just done to cause the code to come on. It seems that it is when I get the rpms up over 5400.

So I reset the code and then logged some data from data blocks 114 and 115 to see what the turbo control was doing. (I can email the excel file if anyone wants.) What it shows is the actual boost starts to deviate from the requested at 5000 rpm and by 5600rpm the deviation is enough to throw a code. Also at about 5000 rpm, the n75 is back up to full (95%)... so the turbo is trying to make up for the lower actual boost reading.

On one of my data runs I was able to catch the car going into limp mode and throwing the code.

I am going to log MAF readings in addition to what I've already logged, to see if the intake measured air volume drops with the actual boost numbers that I'm seeing. I suspect not. In fact I hope the MAF reading follow the increased N75 numbers. In which case I've got an intake leak after the MAF and before the throttle body. If the MAF numbers go down then the MAF is messed up... or I need to get my GIAC remapped to reduce requested boost above 5000rpm.

Now that I know how to make this code happen, if I keep the rpms under 5400 everything seems fine... no code. This might explain why I didn't have the code for a period of two weeks or so... I guess I never got the rpms up over 5400. Also, I might try the stock ECU and get the rpms up there and log some data there too... This might narrow down if I need my ECU remapped. Also, I might actually be able to get the code thrown in stock mode... again, I never get the rpms up to 5400rpm in stock mode.

Anyhow, I just thought I'd update those that are following my trouble shooting of this error.

Kirk

 

What is the deviation at which the fault code is thrown? IE, what's the requested and actual at.

Have you checked where the boost sensor bolts to the intercooler? I discovered one of those bolts missing once.

Does your N75 always stay at 95? Maybe the N75 or lines to/from it are leaking and causing a malfunction in boost pressure control.

 

... at least the numbers change. It has been replaced too. I will re-recheck the vac lines to the n75. I haven't really checked out the intercooler yet... other than the in and out hoses... but I'll check the end caps and bolts and the sensor there now.

The deviation when the fault code is thrown is N75 is at 95% and the boost differences is just over 200 or .2 bar.

I'm glad that I've figured out the situation that cuases the fault... now to narrow the search down to find the leak.

I don't think its the vac brake booster or any sort of vacuum leak anymore. I'm glad I replaced some vacuum hoses though, because they were in very bad shape.

I'll keep you posted.
Thanks,
Kirk

 

<center><img src="http://pictureposter.audiworld.com/19399/n75a.jpg"></center><p>exactly as you describe .. overboost and go into limp.

 

Thanks Yippers. I double checked and the N75 is connected properly.

 

Damn .. I was hoping for the 'easy fix'.