User 52121

Have you done the TCU tune?

I read a few posts on TDI Forum that said a TCU tune with the stock “fixed” ECU tune isn’t much of an improvement either.

Does the Stage 2 at least fix the throttle lag? Or are you guys both equating throttle lag with turbo lag?

RomSL

Stage 2 does help with the throttle lag when it’s below 70-75 outside.
I haven’t driven a stock pre-fix CD and I don’t know how it should behave, but a pre-fix TCU alone makes a significant change.

Needsdecaf

There is absolutely no way a TCU refresh is going to improve this situation. Sorry. This is NOT an issue of being in the wrong gear whatsoever.

User 52121

I really just need to drive a combination of CD's:
- A post "fix" vehicle with pre "fix" TCU
- A post "fix" vehicle with post "fix" TCU and Malone tune
- A post "fix" vehicle with pre "fix" TCU and Malone tune

I have tried to pay more attention to the vehicles behavior, especially with the throttle lag.... now that it's finally warming up outside. As I think it through, I can see how it'd be caused by a combo of tune, regular old turbo lag, and TCU tune.

Specific to ECU tune:
It seems that there is a very sharp cutoff at ~1500rpm or so, for boost and performance. Below 1500rpm, if the converter is locked, in 2nd, 3rd, 4th, and 5th, it's absolutely dead. Nothing happens. Right at or around 1500... everything seems to wake up. I feel the engine load up, suddenly I get a little vibration through the chassis as the motor loads, then I hear the turbo spool... and off we go. Except for 7th or 8th (and 1st, but 1st is so short....) - if I'm wallowing around below 1500 in 7th or 8th and roll into the throttle, I seem to get engine load + turbo spool almost immediately. Which leads me to believe that this is in the engine tune - they're cutting out fuel and boost at lower RPM in specific gears.

Specific to TCU:
It feels like the trans likes to leave the converter locked. So in the usual-described scenario (slow down for a turn, then step into it to accelerate once you're done turning) - I've found the trans will downshift to 4th, or 3rd, depending on speed.... and there you are right at, or just below 1500. Nothing happens, the converter is locked, you just sit there. You either wait to crest 1500, OR you put your foot down and wait for the converter to unlock and the trans to downshift.

Specific to lag:
When you combine the above - you have a chicken/egg scenario. No fuel means no boost, no boost means no fuel. Keeping the converter locked doesn't allow you to generate some exhaust energy to spool the turbo and get fueling to match. Typically you dump in extra fuel to spool the turbo - but that presents an emissions problem. My theory is that, below 1500rpm, pollution was very high so they cut the legs out. On a hot or humid day, the lag is inherently worse just due to lower air quality... combined with the ECU tune, you have our issue.


Just my theory.

RomSL

I tried both - prefix TCU and Malone tune. I couldn’t care less about your statement, sorry.

RomSL

Exactly. It’s a combination of different reasons. Pre-fix TCU allows engine to rev in low gears, which helps with the lag a lot.

chsu74

Thereby locking the low gears giving better mpg and crappy lagging?

hotrod2448

I'll start of by saying I'm not familiar enough with the specific control strategies at play or sensor locations to be confident in any of this but, I'm about to make a lot of WAGs here and I haven't had my coffee yet so, this may not be totally coherent...

To me the big question is what is root cause of this behavior being so much more prominent in the heat? Is it a function of the emissions monitoring equipment performing as intended and not allowing the vehicle to respond to limit emissions, a giant hole in the mapping or a perfect storm situation where the engine and TCU aren't on the same page? It would seem unlikely that they would be so far off on being able to meet emissions (with the revised equipment and tuning) from other manufacturers with similar technology and displacement engines (Specifically BMW and MB) who don't have this drivability issue that it must function this way to be legal. I would also hope that a group of engineers would be able to get the mapping closer than this even in a rush or at least release a patch to address drivability for those of us who have complained about it.

So, due to a lack or error codes I would say we have to assume it is functioning as the software wants it to. What in the system is related to temperature that varies significantly with changes in ambient? Intake Air Temp, whatever they have for reading charge temp out of the intercooler are the only ones I can think of. I do wonder if something as simple as clamping the voltage on the intake air temp to a certain upper threshold might resolve the issue by just keeping the ECU from going into that area of the map. We might get some kind of code for IC efficiency being low or something like that. Or if eliminating the EGR system may help. I wonder if when you go into a deceleration situation does the EGR usage go way up, heat soaking the intake system and causing the engine not to respond until it can pump some fresh air through to cool everything down to a happy spot.

IDK, It's frustrating. You would hope a tuning company would be able to fix this fairly easily with the tools they have to monitor the engine and see which parameters change significantly from it being 50° to 90°.

RomSL

Locking TC may lead to better mpg, but I think there are other factors such as delayed injection that negate improved mpg.
Crappy lagging at low rpm - yes, locked TC won’t let an engine pass the “dead zone” quickly.

Needsdecaf

Fantastic, thanks. Would love to hear how I am wrong.

visitador

^^^ before this becomes a p*** contest, lets withhold opinion until we drive a TCU fixed one. It seems that mod is quite popular in the Touareg forum. Either there are lots of sheep or that mod actually works

booch

I'll post my first hand observation for the third time in this thread; I had an EGR replacement done, post-fix, which included a carbon build up cleaning. The removal of carbon completely eliminated any lag that the 'fix' introduced. Aside from the transmission laziness, which is 'laggy', the car drove like new. The trans laziness is easily addressed with driving style, but the 'lag' was not. The cleaning removed the lag 100%.
After 29k miles of driving since the CBU cleaning, I am starting the notice the lag coming back, slowly but surely. There is definitely a lag impact from carbon build up, which I think the 'fix' tune is much more susceptible to compared to the stock tune. With 151k on the clock, I am not sure how much longer I plan to keep this CD, but if I replace it, I'll very likely replace it with another one. It's been very reliable, still regularly gets 28+mpg, and drives great.

User 52121

Well - the difference between the VAG compliant products, and everyone else's compliant products... is that everyone else designed their product to be compliant from the get-go. They had years of development and calibration time on them. The VAG "fix" was developed in a hurry. It was likely the first thing they came up with that hit their minimum standards for the EPA to be happy, while still being somewhat driveable. Depending on how much testing they did - they likely never (or rarely) encountered the issue we are seeing. I, and several others, have reported that the lag issues seemed to worsen over time. The first few months I drove my post-fixed CD, I felt no difference to it's pre-fix performance. There's also some people here that report they aren't experiencing what we are experiencing - so maybe the test mules VAG did the calibration work on match those specific production vehicles.

2nd sentence - yes, agreed, and is part of my theory.

First sentence - definitely possible. Tho I think "emissions" was VAG's primary goal.

Yeah I've seen comments from both sides. Some say "OMG IT'S FIXED" and others say "Meh." The challenge with the internet - you don't actually know the person on the other end.

I'l still very, very intrigued by this. I wish the EGR wasn't such a bitch to get to on these - from what I've read, it's pretty buried. IIRC "the book' says 8-10 hours to R&R the EGR valve. If it were simple - I'd try it myself. I'm not afraid of labor, and am very mechanically inclined... but tearing deep into the engine Vee on an expensive vehicle that's still under warranty gives me pause.

I wonder what Porsche would charge for a "carbon cleaning". I know when my wife's VW GTI needed it, it was ~$350 in labor... involved cleaning the head and intake manifold. I think it was less labor intensive than what's needed on our 3.0 TDI's though.

skiahh

I disagree. Mine is always in the wrong gear and the more I think about it, the more I'm convinced it's not the engine - or not primarily the engine - fix tune, but the TCU. I've been paying close attention to everything as it warms here, specifically, listening. When I press the accelerator, I hear the engine spool up, but nothing happens, even the RPM indicator doesn't seem to match what I'm hearing, rising slower than the engine sound changes. When the TC locks up (and it's a pretty hard lock when it does), at about 2200 RPM, I shoot off and I have to quickly take my foot off the gas.

When slowing, the transmission is slow to drop to the right gear. Or at least show it's in the right gear. It just sits where it is, kind of like momentum. It stays where it is unless acted upon, and then only after it considers it for a couple of seconds.

And the post fix TCU drives the transmission to the lowest possible gear it can handle, even if it lugs the crap out of the engine, as if it's always trying to force the engine to idle RPM. For example, driving down the street towards my house at 40mph, it'll shift to, and stubbornly hold, 7th gear, putting the RPMs at 1200 and the engine lugging like crazy. Pressing the Sport button does nothing. That mode hasn't been detuned, it's been eliminated! It'll shift to 6th if the RPMs go below 1150 and hold 6th for a while before shifting back to 7th. While in 7th, when the road tilts up, it still holds 7th until it's about to stall and then kicks to 6th.

On the other hand, if I press the accelerator, even part of the way down, the gear indicator will change in rapid succession from 7-6-5-4, where it should be for the hill or to accelerate. And then try to get itself back in 7th (or 6th at 35, or 8th at 50) as fast as it can.

So yes, it's frequently in the wrong gear and keeps it as long as it can!

I think you have it backwards, especially on the decel to accelerate scenario. When I slow, the TC unlocks, with a clear change in RPM from speed appropriate to parked idle (~800). At about 22mph and 3rd gear, the RPMs will drop to full idle, even though the trans indicator shows 3rd gear still. And it holds it until maybe 17 or so, where the indicator will shift to second. Occasionally, the RPM needle will blip, but more often, it just sits there at idle RPM. So when accelerating, it takes time for it to all lock back up again, after the dumbed down TCU figures out which gear it needs.

And to test my theory, I've been driving it in manual mode, which seems to keep the TC locked much longer, before the computer takes over from you, and operating in manual noticeably decreases the lag, as well as the surge; even eliminating it if I get the shifts timed right (and it's much harder to do than in a 3 pedal vehicle!). If I can keep the TC locked and in the right gear, there is virtually no lag. The shift from 3rd to 2nd is the most critical in the decel/roll on scenario. Passing or merging is much simpler, typically just requiring a quick paddle or pull on the gear selector.

[edit] In the mid-speeds with no slowing, it may be a locked TC and the transmission in the wrong gear (and not anticipating the right one) that causes lag in acceleration. So when you hit the gas, the engine tries to spin up but since the transmission is daydreaming, it's in the wrong gear and takes a couple of seconds to get is act together, the engine computer stops increasing RPM, causing that lag, until everyone's on the same page again.

However, at 2200 RPMs, there is still a noticeable surge, so I wonder if there's a turbo wastegate piece to this puzzle, too.

In auto, if I slowly add gas, the lag isn't as noticeable, either, but I think that's because the gentle - and by gentle, I mean barely pressing the accelerator - acceleration gives the TCU time to get its head out of its *** and select the right gear. But you still don't get up to speed any faster, you just don't get the lag/surge dance.

I'm also wondering if the 10 year/120K mile warranty was incorporated because they know the engine might lug itself to death and/or the transmission, with the delayed and then hard lock, is going to **** itself down the road? Certainly not included out of the goodness of their hearts or any true concern by regulators, who were just after some deep pockets to raid.

booch

They had my car overnight but based on the time of drop off and pickup, I can't imagine they spent more than 8 or 9 hours in total on the job.