Observations on Summer Weakness - ALH

'In the past few days, it's been quite warm again, and I could definitely feel the typical summer sluggishness in my chipped ALH Leon. I haven't connected a laptop or used any diagnostic tools, but my 'butt meter' is very sensitive and tells me...'
reliably provides information about the current performance level. And once again, I noticed the following:

Am Anfang der Hitzeperiode war die Sommerschwäche deutlich spürbar. Nach einigen Tagen wurde mein ALH wieder lebendiger. Die Höchstgeschwindigkeit wird eigentlich immer erreicht. Es ist der Durchzug im gesamten Drehzahlbereich. Besonders deutlich sind die Unterschiede im 4. bzw. 5. Gang zu spüren. Die gleichen Beobachtungen konnte ich auch schon früher machen (bei Änderung der Großwetterlage). Kann es sein, daß die EDC quasi das Wetter beobachtet und nach einiger Zeit den Leistungsverlust durch unterschiedliche Maßnahmen ausgleicht? Ich muß dazu sagen, daß ich jeden Tag die gleiche Strecke fahre und auch die versteckten Steigungen bzw. Asphaltabschnitte mit hohem Reibwert, Bodenunebenheiten etc... kenne. MeMy observations are based on the following circumstances:pages:

- Klima an/aus, gleiche Tankstelle, Beladung, Tageszeit (Temperaturen), Strecke, Fahrweise, etc...(Was hab ich noch vergessen ) Ich fahre den Leon nun seit 25.000 km (10 Monate) und habe ein gutes Gespür für sein Leistungsvermögen.

Is this kind of behavior common, or is it unusual?

SeatLeon wrote:

In the last few days, it has been quite warm again, and I could clearly feel the typical summer sluggishness in my chipped ALH Leon. I haven't connected a laptop or used any diagnostic tools, but my "butt meter" is very sensitive and tells me... verlässlich Auskunft über das aktuelle Leistungsniveau. {

.

Hi.

Don't take it personally, but I no longer find much value in personal and subjective impressions when describing

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objective

quantities like acceleration.

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Am Anfang der Hitzeperiode war die Sommerschwäche deutlich spürbar. Nach einigen Tagen wurde mein ALH wieder lebendiger. Die Höchstgeschwindigkeit wird eigentlich immer erreicht. Es ist der Durchzug im gesamten Drehzahlbereich. Besonders deutlich sind die Unterschiede im 4. bzw. 5. Gang zu spüren.

Have you ever considered that it might simply be a matter of your speedometer getting used to the lower acceleration level?

:wink:Kann es sein, daß die EDC quasi das Wetter beobachtet und nach einiger Zeit den Leistungsverlust durch unterschiedliche Maßnahmen ausgleicht?

Then, in my opinion, it would have to constantly reprogram itself to become "more intelligent," but I don't believe that such a thing is yet implemented in our current computer systems.
And if so: why has this never been exploited for advertising purposes

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?

Ich muß dazu sagen, daß ich jeden Tag die gleiche Strecke fahre und auch die versteckten Steigungen bzw. Asphaltabschnitte mit hohem Reibwert, Bodenunebenheiten etc... kenne . . .

I believe I can say the same about myself, and sometimes my tractor feels particularly strong or weak.
If I then perform one of the simplest objective tests – namely, measuring the draw time at 2000-4000 rpm – I always get the same result within the measurement error range, except for the well-known }simple and constant} temperature dependence.

You might want to try that sometime too...

Tomorrow I'll be driving my 'test track' again.

Since the weather forecast is predicting tropical temperatures again, it's perfect [for something].

Let's see what the LL and diesel temperatures do.

CU Gremlin.

Gremlin wrote:

Let's see what the LL and diesel temperatures do.

Hi Ralf,

"Why don't you log the quantity limits? I think that could be more informative."
Normally, the torque limit should be the primary factor when there is sufficient airflow.
However, if the soot limit is lower, this indicates a measured "lack of air."

And the diesel temperature should, in my opinion, be compensated for by an increase in volume...
but wait :
To compensate for the lower density of diesel fuel, the EDC extends the injectiontime.
The latter, however (following the discussions about the turbo tuning article), means a reduced engine efficiency because the longer injection time also means that complete combustion takes longer to achieve complete.

Could this perhaps be the underlying cause of summer sluggishness, even if there is no lack of air (due to excessively hot air) ?

'Why don't you log the quantity limits? I think that could be more informative.'


'I'll definitely do it.'


Could this perhaps be the underlying cause of summer sluggishness, even if there is no lack of air (due to excessively hot air) ?

Well, the existing logs show that the problem with the initial acceleration is likely due to the rapidly increasing intake air temperature when the car is stationary or in stop-and-go traffic.

I hope it will also be the predicted 30°C or higher tomorrow, so that the liquid cooling system gets a proper workout.

CU Gremlin.

@ Ulf


Okay, here's a really dumb question about summer weakness.

Have you ever, or has anyone else, written a letter or email directly to the factory?

They are probably familiar with this 'problem' as well, and if you could find the right employee, they might be able to explain it, and we could then post the answer here.

Just a thought on my part...

Okay...

Next measurement completed.

Extreme heat outside and incredibly high intake air temperatures...
I once logged the fuel injection limitation data (of course, I completely messed up and also logged the actual amount being injected). But the limitations were always above what the driver was requesting.

Outside temperature: 33-35°C. Tank filled to 85%. Logging starts approximately 1.5 hours after turning off the engine while the vehicle is parked in the sun.

Diagram 1 shows the speed, diesel consumption, and LL temperature throughout the entire route. The first red line indicates entering the urban area, the second line marks the stop-and-go traffic, and the third line represents a red traffic light.

Diagram 2 shows the quantity limit as well as the accelerator pedal. Since the off-road section was not significant, I only took the time from the first red line.

It should be clear that the mill doesn't perform as well at a low-level temperature of around 50°C compared to around 20°C in the winter.

CU Gremlin.

Gremlin wrote:

but the limitations were always above the driver's wishes. Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. das die mühle bei ~50° LL-temp nicht gescheit zieht gegen über ~20° im winter dürfte klar sein...

Hi Ralf,

I'm not quite understanding this direct logic yet.

Even with this extreme heat, if the system limits the fuel injection amount despite being set to full throttle, then it will certainly do so even more in the winter.

Therefore, at full throttle, the same amount of diesel fuel should be injected, whether it's summer or winter, regardless of whether the engine coolant temperature is 20 or 50 degrees Celsius .
Therefore, the summer sluggishness must be caused by a reduction in engine efficiency, and we only need to find the cause of the latter.

As an explanation, I'd like to reiterate that the injection times are extended to compensate for the lower density of the hot diesel fuel, which reduces efficiency.
It's possible that VAG combined this with a more conservative increase in fuel volume, so that even in extreme heat, unsightly soot clouds are not visible - because, as far as I know, longer injection times increase the soot value to a greater extent than an equally increased injection rate (mg / °KW).

Does anyone know of any other approaches?

um...

Okay, I need a log of the actual injection amount at both high and low temperatures first.

You are aware that air at 60° has a lower density than air at 20°, right?

Since the maximum boost pressure is a fixed value, it cannot compensate for density differences, which leads to reduced diesel injection to prevent knocking.
That's why they install those damned coolers .

oder ist mir jetzt die hitze zu kopf gestiegen ?

CU Gremlin.

Gremlin wrote:

dir ist schon klar, dass luft mit 60° eine geringere dichte hat als welche mit 20°.

Hi Ralf,

Yes, of course - as long as they are each under the same pressure .

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now, but the maximum boost pressure is a fixed value

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Okay, here's the translation:

"Kind of... In a system description for the industrial TDI engine, it states that the intake air temperature is used as a (fine) correction factor for the boost pressure..."

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kann er die dichteunterschiede nicht ausgleichen -> weniger dieseleinspritzung zur russvermeidung...

If a TDI engine has approximately 20-30% excess air at "normal" outside temperatures, one could initially reduce this reserve during tropical heat to maintain performance – even without immediately causing soot due to lack of air .

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That's why they install those damn coolers

.

I see it a bit differently: for me, the worst bottleneck in the intake system is the inlet valve, which opens only briefly and is quite narrow.
Basically, only a specific (speed-dependent) gas volume can pass through each hub.
And to fit as much mass as possible into this volume, the pressure should be high and the temperature low at this narrow point of the intake manifold .
If the Lambda Control System (LLK) were removed, the Mass Air Flow Meter (LMM) would report a lower mass airflow rate at the same boost pressure.
An alternative increase in boost pressure would again reduce the engine's efficiency due to the increased power required by the turbocharger.

But, as I said: as long as there is still "excess" air mass available (i.e., soot limit > driver request or Nm limit), the charge air temperature should, in my opinion, not matter... ?

Unless, at a higher LL temperature, the effective power decreases despite the same injection amount .
-> Where are the trained mechanical engineers ?

Hello.

. . . in einer Systembeschreibung des Industrie-TDI steht z.B., daß die LL-Temp als (Fein)Korrektur für den Ladedruck herangezogen wird . . .

According to the formula m = p*V/(R*T), at a charging temperature of 50°C, an absolute pressure of 2.2 bar is required to have the same amount of air in the cylinder as when the charging temperature is 20°C and the absolute pressure is 2 bar.
'Therefore, an increase in boost pressure from 1 to 1.2 bar would be necessary. This would significantly increase the compression end pressure and temperature (estimated at approximately 10 bar and 100°C after a rapid isentropic process). Consequently, the peak pressure and temperature would also increase considerably.'
So, I can't imagine that the reduced air mass can be completely compensated for by simply increasing the boost pressure.


But as I said: as long as there is still excess 'air mass' available (i.e., soot limit > driver request or Nm limit), the intake air temperature should, in my opinion, not matter... ?


'I'm sorry, I don't understand. Could you please explain these limitations to me? The only thing I've learned so far is the regulation regarding the lambda value. A minimum lambda value is determined, which then defines the full load. Due to current emission regulations, a higher value is being used to reduce soot and NOx emissions.'
And depending on the air mass, this minimum lambda value determines the maximum injection quantity for full load operation.
But where does this additional torque limitation come from? How is the existing torque measured? Yes, I know that you can get a value using VAGCom, but isn't that just an estimate and doesn't it have any regulating function? If the torque is limited, why can there be increases in performance? But how it's measured is certainly the main question for further discussion about the 'summer weakness.'

Best regards, Ernst.

But where does this additional torque limitation come from? How is the existing torque measured? Yes, I know that you can get a value using VAGCom, but isn't that just an estimate and doesn't it have any control function? If the torque is limited, why can there be increases in performance? But how it's measured is certainly the main question for further discussion about the 'summer weakness.'soot Ernst

The torque limitation primarily serves to prevent damage to the powertrain. The EDC system has the ability to recognize the selected gear based on engine speed and vehicle speed, and then limit the maximum torque accordingly.
The torque is indeed only calculated, but that's relatively easy to do. The value will be approximate, but that's sufficient.

'Increased power isn't really an issue, especially with a stock engine. And when it comes to chip tuning, you already have access to all the parameters anyway, or you can simply disable the torque limiter.'

However, this characteristic does not influence summer weakness.

CU Gremlin.

Ernst S. wrote:

Quote: But as I said: as long as there is still excess "air mass" available (i.e., soot limit > driver request or Nm limit), the intake air temperature should, in my opinion, not matter... ? "I'm sorry, I don't understand. Could you please explain these limitations to me? The only thing I've learned so far is the regulation regarding the lambda value. A minimum lambda value is determined, which then defines the maximum load. Due to current emission regulations, a higher value is being used to reduce soot and NOx emissions." Und je nach Luftmasse ergibt sich dann über diesen minimalen Lambdawert die maximale Einspritzmenge für die Volllast.

Hi Ernst,

As far as I know, the TDI software architecture has 3 main control parameters for the injection quantity.

"Accelerator pedal position = driver's desired input, which is converted into a desired fuel injection amount based on engine speed."

"Soot limit/soot map = how much fuel can be injected at the current air-cylinder filling (mg/stroke) and engine speed to avoid excessive soot formation?"

3. Torque map or torque limitation: How much fuel can be injected at the current engine speed as a maximum, without overloading the powertrain?

These 3 calculations run constantly in parallel, and the currently lowest result determines the "approved" and to-be-adjusted injection amount.

Therefore, as long as the soot threshold is higher than the torque limit, there is "more than enough" air available in the cylinders. This means that the lambda (air-fuel ratio) could be significantly leaner until the reduced mass airflow measured by the MAF sensor brings the soot level down to the same level as the torque limit.

Only when the intake air temperature continues to rise and the mass airflow signal continues to decrease would the injection quantity be reduced as a result of excessively hot air.
However, that wasn't the case with Ralf's logs; in those instances, the driver's preference was always the lowest.

Okay .

slightly off-topic:

You can only read the calculated torque with a VAG Com on PD TDI engines, or have I missed something? I haven't found a corresponding measuring block in my ALH Leon or in a friend's AFN Ibiza.

Hi.

'Accelerator pedal position = driver's desired input, which is converted into a desired fuel injection amount based on engine speed.'

'Soot limit/soot map = how much fuel can be injected at the current air-cylinder filling (mg/stroke) and engine speed to avoid excessive soot formation?'

3. Torque map or torque limitation: How much fuel can be injected at the current engine speed as a maximum, without overloading the powertrain?


I'm glad that the 'torque limitation' refers to the torque curve. A drivetrain protection program that measures (or estimates) torque somewhere and then adjusts the fuel injection amount would have surprised me greatly.

The torque map and its limitations, in addition to the various loads on the engine and the rest of the powertrain (if developed jointly), also affect the soot emission characteristics. The fuel injection quantity limitation based on air mass is then an optimization for reducing soot emissions, especially for dynamic performance (e.g., full throttle after thrust cutoff).
In the steady-state full load range, the two limits should ideally coincide (during design). The engine developer has already calculated the required lambda value beforehand to achieve the desired soot emissions. A higher air mass flow rate (due to increased boost pressure) would be pointless.
And the maximum possible driver preference should also be the same value.

Whether the other settings related to load adaptation (torque limiting) that the VAG Com provides are included is not so important for understanding summer torque lag. However, it would be crucial to know how these settings interact with adjustments for air intake temperature, ambient temperature, diesel fuel temperature, and intake/ambient pressure. This information would allow us to analyze the logged data to identify potential causes of the summer torque lag and determine whether it is intentional or simply something that could not be compensated for.

For example, the increased air mass at low temperatures could definitely be used to achieve higher performance. However, this should be visible as a change in the torque limit value in VAG Com (or it might not be visible if the fuel injection quantity has been adjusted but is not displayed under 'Nm Limit rpm' in VAG Com).

If the airflow is designed for a low temperature due to the boost pressure, then it's possible that at higher temperatures, the airflow could limit the fuel injection amount even under prolonged full load. This is normal in dynamic conditions. However, if you were to see something like this during a dynamometer test, it would be an explanation.

Ich glaub aber fest daran, daß man einfach die volle Luftmasse, die bei einem über die Temperatur fast konstanten Ladedruck zur Verfügung steht, ausnutzt. Durch eine Anpassung der Drehmomentbegrenzung. Vielleicht kann ja mal wer eine höheres 'Nm Limit rpm' im Winter loggen. Aber wie gesagt weiß ich nicht ob die Anpassungen da auch drinnenstehn, weil eine Lastwechselanpassung z.b. kann ich eher nicht erkennen. UAnd then those temperature and pressure adjustments don't necessarily have to be included there.

Best regards,
Certainly! Please provide the German text you would like me to translate into English. I will only provide the translation.

Ernst S. wrote:

The torque map/torque limitation, incidentally, in addition to all the loads on the engine and the rest of the powertrain (if they were developed jointly), also affects the soot characteristic curve. In the steady-state full load range, the two limitations should ideally coincide (in a well-designed system)

.

Hi Ernst,

In reality, however, the soot limit would eventually be reached due to contamination or aging of the mass airflow sensor (MAF), causing it to fall below the torque limit over time.

Probably, therefore, the torque limit is set slightly lower "from the factory" to allow (initially, with a new mass airflow sensor) some leeway for such occurrences without immediately losing performance --> otherwise, this could lead to justified complaints about reduced power still within the warranty period .

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The engine developer had previously calculated the required lambda value for the desired soot emissions. A higher air mass flow rate (due to increased boost pressure) would be pointless.

Generally speaking, that's correct, but... -> see above.

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Und der maximal mögliche Fahrerwunsch soll dann natürlich auch der gleiche Wert sein.

Ist aber zumindest beim AFN nicht der Fall: dort kann der Fahrer per Pedal mehr Diesel anfordern, als die "starre" Drehmomentbegrenzung bei der betr. Revolutions allowed.

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However, it would be important to understand how the adjustments are made for intake air temperature, ambient temperature, diesel temperature, and intake/ambient pressure. This is so that one can infer potential causes for the summer performance issues from the logged data, and whether they are intentional or simply could not be compensated for.

So, the soot map consists only of engine speed, air mass/stroke, and fuel mass, without being influenced by intake air temperature.

As far as I know, the ambient pressure sensor is only used for overspeed protection of the turbocharger, for example, in high mountain areas.
Of course, it also has an influence on performance from a certain height , if the absolute boost pressure is reduced so much that, due to the resulting lower mass airflow sensor signal, the soot map suddenly becomes the "effective" injection quantity limiter.

I'm still focusing on the diesel temperature issue.
The lower density of the hotter fuel is compensated for by extending the injection duration "backwards," which shifts the overall process more towards a state of equal pressure and thus reduces efficiency.
Ob das allerdings schon die gesamte Sommerschlappheit erklären kann, weiß ich nicht . . .

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For example, the increased air mass at low temperatures could definitely be used to achieve higher performance. However, this should be visible as a torque limit in VAG Com (or it might not be visible if an injection quantity adjustment has been made but is not displayed under "Nm Limit rpm" in VAG Com)

.

Last summer, I tried the DZR (Direct Injection Resonance) experiment with increased boost pressure, which means more air mass. However, the stopwatch showed no improvement whatsoever.
Therefore, in my opinion, the air mass was not the actual limiting factor.

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Wenn aber der Luftmassenstrom durch den Ladedruck für eine niedrige Temperatur ausgelegt ist, dann könnte es schon sein, daß bei höherer Temp. die Luftmasse die Einspritzmenge auch bei längerer Volllast begrenzt.

However, it should be possible to disable it by increasing the boost pressure. The result is shown above .

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Ich glaub aber fest daran, daß man einfach die volle Luftmasse, die bei einem über die Temperatur fast konstanten Ladedruck zur Verfügung steht, ausnutzt. Durch eine Anpassung der Drehmomentbegrenzung. Vielleicht kann ja mal wer eine höheres "Nm Limit rpm" im Winter loggen.

I don't think so: The "torque curve" of the AFN is actually just a simple table with RPM and mg/stroke values. So it's not affected by temperature at all.

Furthermore, the actual performance would then depend on a very "sensitive" measurement, with the "successes" described at the beginning.