Boost Spike and Diagnosis

Followup

When Jeff (RocketChip) was reprogramming my ECU, he stuck a vacuum pump on my VNT actuator, and you could hear the mechanism letting go after in overcame some initial stickyness.

Last weekend I pulled the intake and cleaned it (plenty of gunk), adjusted the VNT actuator, and cleaned the turbo. It was the actuator itself that was sticking, not the turbo mechanism.

I had swapped MAFs and N75s earlier, but neither made a difference.

Now my boost graph looks like this: (Note that this is with RC2, and the earlier graph was stock)

XJCoupe,

Did you replace the actuator or were you able to clean and exercies it back into health?

Your graph still has the same shape. Slightly higher than specified, yes. Narrower, yes. But it still peaks, settles and then rises to an approximate steady state. The important difference is the peak is now nearly equal to the steady state.

Thanks,
Bryce

Hello all,

I replaced my N75 this past weekend and haven't gone into limp mode yet. A new graph shows it actually stabilizes now, while it really didn't before. I still don't like the big boost spike, but maybe it's always been that way... I really don't know - never tried using vag-com when the car was a bit newer to record this data before I had a problem. The graph, tbh, looks almost the same as the graphs of mine on page 2 of this thread ... but, anyway, it didn't go into limp mode yesterday, so I'll just see what happens next time I go on a drive and can test it. I hope it's fixed. Otherwise, the VNT actuator is the only thing I haven't replaced.

So, what I've done already. Taken intake and exhaust off, along with head. Cleaned everything. Took turbo apart. Cleaned it. Vanes moved pretty well before, and after cleaning they moved very freely. I replaced the MAF. I have now replaced the N75. I have checked all vacuum hoses for leaks. None of them leak. Nothing much else to do except replace the VNT actuator. I suppose I could try and get the VNT actuator off and adjust it. Are you supposed to shorten of lengthen the VNT actuator rod to minimize the boost spike?

Below is a new graph.

p1550 and limp mode

By "Limp Mode" is the car running but will not respond to throttle input (at all) until you shut the car off and restart it, or when you are in the 2500-3500 rpm range and push down on the accelerator, the car just doesn't respond,(with normal torque) but is still drivable? I have had both issues in the past and currently chasing p1550 again.
One post put me in the right direction last year... check your vacuum hose on the ECM (or ECU) it is in the firewall on the passenger side. There is a link some where on TDIclub to this procedure. if I find it I will post it. But that hose will cause the problem you have incountered

Here's another new graph, just to finish off the thread. I took my intake and exhaust off again this year, had to drill out the bolts in the turbo to get the vane assembly out, but cleaned it thoroughly, made sure everything was free, and put everything back together.

Now look at the new graph of 5th gear, full throttle. Small spike and then specified boost is tracked the whole remainder of the time. Looks good!