Throttle Lag: Initial Torque Drop Explained

Hello,

I'm experiencing the following issue at approximately 2200 RPM with a warm engine:

"I often notice that when I accelerate more forcefully below 2200 RPM, the engine seems to hesitate (slightly slows down) before gradually starting to pick up speed."
If I only give it a little gas and slowly press the pedal according to the increase in engine speed, the motor immediately responds and generally achieves the best acceleration values.

What could that be? It sounds like the actual motor parameters are different from what the sensors are indicating, which is causing incorrect regulation.

Greetings.
Andi.

Wouldn't it be best to troubleshoot this using a logic analyzer to see where the problem lies?

Okay,
Today I logged some data. After the first block, I unplugged the electronic controller for the turbocharger and plugged it back in after a while. I had done this before when the engine was cold, and I got the impression that the engine responded better to the throttle.

I glanced at it (I'm not an expert in diagnostics).
You haven't reached the target of 1000 mg of air mass within the first 2500 minutes.
Still showing the target boost pressure, as far as I can see.
He would have to leave eventually, wouldn't he?

Yes, the setup is very slow.

Could you try driving in 4th gear, going uphill as much as possible, or in 5th gear, and then keep the accelerator pedal fully pressed consistently... This would help with understanding the data and identifying the engine's behavior.

Yes.
Okay, so maybe try giving it full throttle around 1700 and 2000 RPM, wait a bit, then do it again, and keep waiting until the initial setup process is complete. Then, try using less gas, like you said, "that's better than full throttle."

The logs are located on the fourth floor, except for the last one, and I'm not entirely sure about its location.
On the second sheet, three graphs are shown. The second one showed some improvement.

Above approximately 2200 RPM, it always runs well. And when the engine is cold, it responds very well to acceleration in the lower RPM range.

I got the impression that the entire effect is time-dependent.
Often, when I'm driving at around 1700 RPM for a while, and I gently press the accelerator pedal just a little bit more, and then after a few seconds, really give it gas, it pulls strongly even in 6th gear. But when I accelerate quickly and shift through the gears, it feels very sluggish.

I suspected the AGR valve might be closing too slowly. I need to try putting a shim in it over the next few days to check that. But with such a complex control system and all those sensors, another control effect could potentially counteract that.
Can the turbo run sluggishly when it's hot? I don't hear it spooling down after I turn off the engine. However, it still whistles during operation.

By the way, this behavior is very similar to what I experienced with my old AFN when the variable turbine geometry (VTG) was sticking. In the lower gears, it wasn't possible to rev up quickly, and it took about 2-3 seconds for the turbocharger to fully engage.

Have you ever checked the pressure drop and maximum value in a pipeline?
If you're producing a lot of stellar material, the valve has to work hard and may also consume the maximum allowable vacuum pressure. This could then take a long time for the pressure to build up again.

Hold on, I didn't understand that.
Is the AGR opened by vacuum pressure?
That is to say, if there isn't enough vacuum pressure, it can't open quickly or widely enough.
While it would be detrimental to NOx emissions, it would be beneficial for torque and soot reduction.

Okay, I don't understand everything either, but your turbo control seems to be working slowly as well. And if the EGR valve doesn't open, there wouldn't be enough usable air mass flow for the engine, which means less fuel injection, resulting in less power, exhaust pressure, turbocharger speed, and boost pressure. This would also mean a slower increase in power output.
That's how I think the connection should be.

Have you checked all the vacuum hoses for cracks? They tend to become slightly porous over time, which can cause them to draw in air and reduce the vacuum pressure.

This could also potentially lead to the charger and the EGR system not being controlled correctly.

You can also try removing the hose from the intake manifold at the EGR valve and take a look inside – if it's completely clogged with carbon buildup, it won't be able to close properly, which will cause the turbocharger's boost pressure to vent into the exhaust.


Your approach of sealing the AGR valve is a good starting point; at least then you'll know if the AGR valve is the problem. Then you could check whether the VTG rod moves freely or "sticks." However, I don't think that's likely, because a stuck VTG usually results in a control error being stored in the fault memory, as the boost pressure exceeds or falls below the regulation limit.


Greetings.
George.

Hello,

Thank you for the answers.

The turbocharger on the V6 TDI is controlled by an electric motor. The connecting rod moves easily when the engine is stationary, at least when it's cold. I haven't tried it yet when the engine is hot.
I checked the actuator diagnostics again yesterday:
The electric actuator for the turbo raises and lowers the variable geometry turbine (VGT) rod. I can't say whether it reaches the end positions because the actuator diagnostic only runs within a range of 20-80%.

The AGR valve makes a loud clicking sound when there's vacuum, so it should be pulled in by the vacuum. I only hear the sound of air escaping from the vacuum system. Shouldn't the closing spring also cause it to snap back into place?

Greetings.

Andi.

Hi Ski_Andi, it's good that the VTG is going electric; that eliminates the issue of external vacuum pressure - you're right.
The actuator tests should ideally be between 20% and 80%; otherwise, it's almost like there's no more modulation. That seems plausible. Once those values are reached, you could have someone check if the VTG (Variable Transmission Gear) is at its limit.

With the LMM (likely referring to a specific product or device), it seems that even with a new component, the 1000mg value is only barely achieved.
Has anything improved since the renewal?

Quote:

The AGR valve makes a loud clicking sound when there's vacuum, so it should be pulled in by the vacuum. I only hear the sound of air escaping from the vacuum system. Shouldn't the closing spring also cause it to snap back into place?

Okay, I'm not familiar with the EGR valve for the V6 TDI engine. But if it's still a pneumatic system, shouldn't it be roughly the same as the one used in the 1.9 TDIs?

And the clicking/popping sound is louder with the closing valve than when creating a vacuum... while the engine is running!

Hello,

So, the language model is still the old one.
It's too expensive for me to replace it just on suspicion, especially since the typical problem with my old AFN engine wasn't a lack of power at high RPMs.

A few weeks ago, I had an A6 Allroad with a 3.0 TDI engine, but it has a different type of mass airflow sensor (MAF) that doesn't fit in the 2.7-liter engine. Therefore, I couldn't do a direct comparison.

Regarding the AGR (Arbeitsgemeinschaft für das Geschlecht).
It's possible that the clicking sound I heard was from the vacuum being released, and if so, it would likely seal properly. It's quite possible that I misinterpreted the percentage value displayed by the VAG-Com. I'll be able to tell when I have a thin sheet of metal inflated.

Greetings.
Andi.

I've been messing around again.

Now that it's so cold, the lower part of his body is working really well. But as soon as he warms up, it gets worse.

"I've noticed for a few months that the very slow increase in speed when cruising at a constant speed changes when I release the accelerator and then accelerate again."
Then it runs smoothly. It's as if the "fuel mixture" isn't correct.

Today, I disconnected the mass airflow sensor (MAF) while the engine was running, just to see if the values generated by the engine control unit (ECU) based on theoretical data would be different. The behavior was almost identical. So, the MAF should be providing reasonably accurate readings.

However, I noticed the following.

My colleague had been messing with the throttle, and as a result, the coupling rod of the VTG would only move 1-2 seconds after the gas pedal was pressed.
That means the engine speed increases significantly before the variable turbine geometry (VTG) rod is moved.
Is this normal, or is it a problem specific to me?

I'm just not sure where the VTG rod should be positioned when the engine is in its unloaded state.