Constant Low Power ALH

I rebuilt the vacuum pump and did the JB Weld fix on the outlet nipple. I have 30" vacuum at idle right out of the pump at the check valve.
I'd say that ia sufficient vaccum but I didn't notice any difference in power...

hmmm, the other time I saw some behavior like this was when Oldpoopie (Justin in Portland) found air bubbles in my fuel from a micro-cracked thermostatic T fitting. I can't remember if you'd addressed that already.

The QA (quantity adjuster) collar's feedback mechanism can't control for air in fuel, as metering is open-looped based on SOI and injection duration and assumed a 'normal' amount of dissolved gas. Bubbles really screw with fuel delivery.

Get a buddy to rev it while you look for bubbles. Wiggle the thermo-T (gently)...if you have bubbles, that can be a problem.

I also don't remember if you watched the VNT vacuum pot move the lever through full range while a buddy gets it on boost? They're known to get sticky, but that would show up on VCDS boost data of course.

What VCDS logging have you done so far?

You need to do fuel actual versus requested and boost actual versus requested on a 3rd gear pull.

I'll check the fuel lines again.

Data Logs:
Block 001: 903/min, 3.6 mg/str, 1.72-1.76V, 90.0 C
Block 003: 903/min, 275 mg/str, 270-290 mg/str, 79.7-81.7% (EGR looks a bit high)
Block 004: 903/min, 0.4 BTDC, 0.7 BTDC-1.1 BTDC, 2.8%
Block 010: 1275 mg/str, 979.2 mbar, 989.4 mbar, 0% (measured with engine off, key on)

For Blocks 008, 010 & 011 running 1500-redline in 3rd gear WOT look at the Google doc I created with tabs for each of these

https://docs.google.com/spreadsheets/d/1_lLX11JYQcCmo4atTRv_BlWFUZ-uUdYK71ftAGF3N3A/edit?usp=sharing

I got a 404 error.

nicklockard said:

I got a 404 error.

Click to expand...

I updated the link. Should work now

Okay, I'm not an expert with VCDS, but it's taking your car 2.5 seconds to meet requested boost level, then it overboosts for nearly 4 seconds.

I graphed boost actual versus requested and N75 duty cycle together (N75 on its own axis). Your tubo's behavior is not correct.

Your N75 duty cycle is wacky. Have you checked the vacuum line routing?

A few thoughts
- I may need to pull the turbo and check the vane ring. There might be some excess wear on it even though it moves freely.

I have not checked my vacuum line routings, but I sure can. I will need to find some routing diagrams to double check against...

I checked vacuum line routing. Though it isn't exactly identical to the diagram, it is routed and serves the same purpose. To rule routing out for sure, I directly connected the N75 to the vacuum pump/booster check valve T. Still no improvement.
I even ran several vacuum tests across the system and isolated several areas and never found a leak.

I will probably try swapping in another N75 again cause I only swapped the N18 / N75. Also probably going to dig into the turbo and see if the vane ring or lever is worn or broke.

Yeah, I'm out of my depth at this point.
See post 11 here: https://www.forums.tdiclub.com/showthread.php?t=480426
And Charlie (KermaTdi) has a pretty good troubleshooting guide here: https://kermatdi.com/i-1326-troubleshooting-turbo-boost-issues.html

Note that the vent port of the N75 should be routed to filtered air from the airbox, not open to atmosphere, or the valve ingests lint and jams over time.

Lastly, check out this troubleshooting thead: http://forums.tdiclub.com/showthread.php?t=493238&page=3

New update:
Had overboost that kept happening occasionally from October 2020 to this spring (2022) and was getting progressively worse; especially on hills, when accelerating too hard and on nice damp cool mornings (dense air). I finally found a used (100k mile) turbo and swapped it in while doing a heater core replacement and also checked the intake (clean as expected).
The limp mode is gone and performance has improved a decent amount. The variable vane ring and/or fingers for the vanes must have been worn enough causing boost control issues for demand vs. actual.

I'm not 100% certain this has taken all performance issues away, but believe it to be a significant culprit.