Underboost Problem Almost Immediately After APR Stage 1 Tune

[Belthasar]

Your turbo is probably covered for 10 years and 150,000 miles. At least mine was.

Really? Was there a class action lawsuit or something? Very interesting.

I suspect a TD1 code would be grounds for invalidation, though.

 

[Belthasar]

Update time, and a renewed call for help.

I was able to install the new CTS actuator without any drama. Before reassembly, I did end up cleaning the turbo hot side around the wastegate arm with some throttle body cleaner, and applied Permatex 77134 Nickel Anti-Seize Lubricant to just about everything that moves in the arm assembly external to the turbo. It's worth noting that the arm flapped around freely before doing so, and had a teeny bit more resistance after lubricating, which is to be expected since the anti seize lube is fairly thick. However, the wastegate was definitely NOT physically binding.

I started threading in the new actuator rod and followed the factory procedure (basically, the ShopDAP video tutorial) for setting the voltage; I fired up VCDS with the ignition in the ON position and selected the following measurement:

Charge air pressure control valve uncond voltage sensor

Tightening the rod, I was able to get this measurement to settle on 3.71v after snugging up the 10mm nut. Satisfied this was within target range, I ran the following:

First Adaptation of charge pressure actuator

This completed successfully.

Reassembly was fairly easy. I was careful to reinstall the downpipe correctly, torquing the v-band, and also took care to make sure the turbo inlet elbow and intake piping were properly aligned and tightened down properly. I fired the car up, heard no obvious exhaust leaks, let it warm up to operating temp, then take it for a victory lap....

... and I was met with immediate disappointment. The lag I described earlier in this thread is still present, as is the "overrun". It's also inconsistent. I do get boost when called upon, but it still comes on so unpredictably it feels like I'm almost back at square one. No EPS light or any codes, but definitely not normal.

New things noticed this time around:

• I can definitely hear a whoosh of air when I let off moderate throttle. Not quite blow off valve-like sound, but something that sounds consistent with the wastegate opening
• I get a rattle when I put it under moderate load
• When I turned off the car, I heard multiple beeps in lieu of the single beep you usually hear when the actuator does its post-drive thing.

This is puzzling. I first wondered if the CTS part required a different method of calibration, but a quick Google search revealed that it's designed to follow the factory procedure. @Diggs24 , is there anything obvious I could have missed throughout this process?

As always, help is deeply appreciated.

 

[Belthasar]

I logged some more data using the same parameters as my runs before changing the actuator.

This was a 3rd gear highway on-ramp pull. Held around 2000rpm, floored it when the coast was clear. Noticeable lag, followed by boost.

This was a 4th gear pull on an open highway with a high speed limit, starting around 45-50mph and flooring it. Again a little lag, but boost came on.

Disclaimer about these data: This time I selected VCDS's "turbo" option, as well as "Group UDS", which significantly improves the sampling rate from what I understand. This is why the new charts seem much smoother.

My eye is drawn to the charge pressure actuator acutal vs specified parameters. Unlike in my earlier logs, it does appear that the wastegate functions as told now, no? Or am I misreading these data? You can still see that boost is not being delivered as requested; the gaps between charge air pressure actual vs specified, as well as the driver intention vs engine torque parameters show when I experienced the lag.

Is a bad diverter valve a possibility?

 

[Belthasar]

Since it's a 5-minute job, I decided to pull off the diverter valve and give it a quick look. I was hoping to find some obvious flaw or tear, but found none:

This is the stock Revision C valve. Yellow o ring appears to be fine, as does the rubber seal. The piston moves perfectly with no obstructions when assembled. The only thing I saw out of the ordinary was some grit inside the assembly:

Upon reassembly, the car still behaves identically to before. I don't know enough about these DVs to know if there can be something subtle that's not visually obvious but affects boost management. As always, any advice is appreciated.

 

[Rollux]

I’d be interested to see throttle body requested position vs actual - starting to see damaged teeth of a few Mk7s throttles of late

 

[Belthasar]

I’d be interested to see throttle body requested position vs actual - starting to see damaged teeth of a few Mk7s throttles of late

Very interesting. I can certainly grab another log with these parameters.

Would a broken tooth fit the symptoms? I suppose it would account for the lag and persistence.

What about the metallic rattle I’m hearing, but only after the wastegate actuator was replaced? That could be something else (like a heat shield), but I’m fairly sure I reassembled everything nice and tight.

And the woosh of air?

 

[Diggs24]

Never heard this issue on a 2.0 or 1.8 motor. You'd get a code if the throttle body wasn't able to hit setpoint. Also, at this airflow level you wouldn't need to full open it anyways.

 

[Diggs24]

I logged some more data using the same parameters as my runs before changing the actuator.

This was a 3rd gear highway on-ramp pull. Held around 2000rpm, floored it when the coast was clear. Noticeable lag, followed by boost.

This was a 4th gear pull on an open highway with a high speed limit, starting around 45-50mph and flooring it. Again a little lag, but boost came on.

Disclaimer about these data: This time I selected VCDS's "turbo" option, as well as "Group UDS", which significantly improves the sampling rate from what I understand. This is why the new charts seem much smoother.

My eye is drawn to the charge pressure actuator acutal vs specified parameters. Unlike in my earlier logs, it does appear that the wastegate functions as told now, no? Or am I misreading these data? You can still see that boost is not being delivered as requested; the gaps between charge air pressure actual vs specified, as well as the driver intention vs engine torque parameters show when I experienced the lag.

Is a bad diverter valve a possibility?

That's the turbo spooling. It's functioning normally.

 

[Belthasar]

That's the turbo spooling. It's functioning normally.

There's no way this is functioning normally. Still way too much lag, much more so than the first day I was tuned. It's also still inconsistent; sometimes it'll boost with minor lag, other times it'll behave like in my original video (floor it, nothing for a few seconds, then boost). Butt dyno also says it's not as powerful as it was the day my tune was done.

 

[Diggs24]

It's an 87 tune. It probably has a major lack of timing down low to reduce the chance of knock.

https://datazap.me/u/geraltofrivia/post-wastegate-actuator-change-data-1?log=0&data=1-2-7&mark=73-81

It goes from 0psi to almost 20psi in 250rpm. That's not laggy at all. It's not just boost that makes power, so does timing.

Next time you run the tank down try a tank of 91 or 93 just for shits and giggles.

 

[Belthasar]

It's an 87 tune. It probably has a major lack of timing down low to reduce the chance of knock.

https://datazap.me/u/geraltofrivia/post-wastegate-actuator-change-data-1?log=0&data=1-2-7&mark=73-81

It goes from 0psi to almost 20psi in 250rpm. That's not laggy at all. It's not just boost that makes power, so does timing.

Next time you run the tank down try a tank of 91 or 93 just for shits and giggles.

Perhaps we're using the term "lag" differently. My data log may support that the amount of turbo lag is normal, but there's a significant lag between throttle input and power delivery, and this lag is very inconsistent. Compared to day 1 of the tune, the car is borderline undriveable right now.

 

[ucfquattroguy]

My vote goes towards the ignition timing theory. Boost pressure building is one thing, but won't mean much until the ECU pours the timing advance in. Check relationship between you requesting torque, boost pressure, and timing change. If it's an 87 octane file, it's not going to immediately give you the beans. Likely going to ease into it to reduce likelihood of knock and/or detonation.

 

[Belthasar]

My vote goes towards the ignition timing theory. Boost pressure building is one thing, but won't mean much until the ECU pours the timing advance in. Check relationship between you requesting torque, boost pressure, and timing change. If it's an 87 octane file, it's not going to immediately give you the beans. Likely going to ease into it to reduce likelihood of knock and/or detonation.

Interesting conjecture, but if this were true, then that would mean that all APR 87 octane tunes actually increase throttle lag compared to the stock tune and, based on how poor the driver experience is in my car right now, almost nobody would be happy with this tune. On the contrary, people rave about it.

Also keep in mind, when I flashed back to stock, this lag problem was still present.

 

[Diggs24]

Highly doubt they put you on your original boxcode. They (tuning companies) all go back to a “stock” file that isn’t your original. Seeing all the various files out there and how they are setup I am not surprised it feels different.

 

[Belthasar]

Put it this way: if you drove this car, there's no way in hell you'd feel that it's operating normally. Press the pedal down even moderately and you'll get an awful rattle, a second or two of no action, then a sudden surge. I know it's hard to describe in words, but I'm willing to bet the house that this is not APR 87 octane tuned normal.