VTG Turbo Lag: Engine Hesitation After Gear Changes

'I have good comparison points, thanks to several TDIs at work, regarding responsiveness. The Tourans have 10x TDI engines, and they respond very well from low RPM. However, what I notice when shifting is that if you immediately give it full throttle again (e.g., going uphill or accelerating), it takes a noticeable second for the full power to come back. Our ATJ engine in the Passat 3B is exactly the same (although not as extreme). Our old 35i with the 1Z engine and its nice old wastegate turbo never had that issue; full power was always available after shifting.'

What's the reason for that? Are there any conclusions that can be drawn about the AGR (Abgastasteuerung - exhaust gas recirculation) rate, which was likely lower in the 1Z? Or is it related to the acceleration of the mass in the turbocharger (as far as I know, VTG turbochargers have heavier turbine and compressor blades)?

Best regards, WarLord.

WarLord wrote:

If you immediately give it full throttle again (e.g., going uphill, accelerating), it takes a noticeable second for the full power to return. Our ATJ engine in the Passat 3B has the exact same issue (although not as extreme). Our old 3.5i with the 1Z engine and the nice old wastegate turbo never had this problem; full power was always available after shifting. What is the reason for that?

I simply think that the newer TDIs (especially the PD models) are more dependent on the amount of air entering the engine for performance reasons, compared to the 1Z/AFN generation. Without boost pressure, the newer, supposedly more powerful engines produce less power than the older ones.

Even the vehicle weight will factor into the subjective impression - a "light" Golf3 will reach a certain speed more quickly than a Touran, even without turbo boost .

Regarding the latter, I'm still mourning the loss of my AFN-G3: it was about ~100 kilograms lighter than the Polo and had a noticeably better punch from idle speed.

Along with the shorter gear ratio, the Golf could accelerate uphill even in 5th gear, with almost no incline being too steep, starting from around 1200 rpm (with just a little turbo boost).

The ASZ engine pulls the same hills, and when it's running well, it does so in 4th gear. Sometimes, I even have to downshift to 3rd gear. Until I shift up, I need to keep the engine speed above 1500 rpm; only then does the ASZ engine really deliver its power.

Well, the thing about turbo lag isn't entirely far-fetched. The 1Z/AFN generation also emerged from turbo lag much more smoothly than the AWX/ASZ generation, no matter what they might be called. Unfortunately, I haven't had the chance to drive a Euro 3 VP TDI yet.

Best regards, WarLord.

WarLord wrote:

Unfortunately, I haven't had the chance to drive a Euro 3 VP TDI yet.

You probably didn't miss much... our ALH Ibiza is already a bit softer in its throttle response and low-end torque compared to the AFN Golf (even considering the lower power output, the ALH should have more to exhibit a similar behavior to the AFN). However, it still pulls with a bit more punch than the ASZ.

The latter one really only relies on the boost pressure, which is about 0.7 bar.
- but it's still a lot of fun after that.

Sure, here's the translation:

"Response from Gremlin (to me, via email):"

Quote:

Unfortunately, I am currently unable to reply in the forum because the proxy is offline... Okay, so I also experienced increasing sluggishness when trying to initiate conversations, which... apparently, it's also a sign of a failing LMM. because since... The diode is being pushed really hard again, just like it was in the beginning. without a moment of reflection.

Best regards, Ulf.

Hmm, I should probably measure the air mass again. I just got a new mass airflow sensor.

Best regards, WarLord.

WarLord wrote:

If you immediately give it full throttle again (e.g., when starting a hill climb or accelerating), it takes a brief moment for the full power to be restored.

I'm also very familiar with the problem of the delay before the turbo kicks in again, and it occurs in all newer TDI models.
For vehicles with Tiptronic transmission, whether it's a V6 or the 1.9 PD engine, the issue can be even more annoying, as it may take up to 2 seconds for the engine to start providing power again.
It becomes particularly noticeable when you're braking and about to enter the roundabout from a flowing lane. If you immediately accelerate afterwards, nothing happens at first, and you become an obstacle as the cars get closer and closer.

The accelerator pedal simply doesn't work synchronously with the engine control unit (whether it's the control of the fuel injection pump, etc.), and this becomes apparent as soon as you try to accelerate with full throttle, which is where VW/Audi still has a significant shortcoming.

BMW seems to be better equipped to deal with this issue.
I once read a report that the release of newer diesel variants was delayed about two years ago. The test engineers reportedly criticized the excessively long delay before the engine produced power, and that the accelerator pedal wasn't working synchronously enough (which somehow seemed familiar to me when I read it). I don't know exactly what the ultimate issue was, whether it was software or the fuel injection pump.

"In my 1996 Audi, this problem doesn't occur, even though it has an automatic transmission. There is a slight delay, but it's well below one second. On the contrary, the car has very good acceleration, making driving an automatic in the city quite enjoyable."
"Unleashed power without gear changes."
And that is correct!

Es muss eine Softwaresache sein, bei den Benzinern kann man es via neuer Software rausholen (wobei die Gedenksekunde anders ausgeprägt ist). Bei unserem ATJ (dem 115 PS PD nach dem AJM) ist es noch nicht so ausgeprägt. Es kommt auch gleich Schub, wenn man Gas gibt. Es ist nur so, dass der richtige Turboschub erst nach der Gedenksekunde kommt. Dies war bei unserem alten VP TDI (1Z) nicht so. Auch kann ich mich erinnern, dass es beim ASV im Octavia, den wir mal als Leihwagen hatten, auch nicht so war. Just spontaneous.

Best regards, WarLord.