ALH Turbo: Adjust Boost Pressure - Read This!

Hello,

Unfortunately, I can't ask the question in the correct thread because I'm not wearing a blue work uniform. I hope you can still help me.

I have the following problem:

We modified the engine of a good friend.

It's an ALH engine, fitted with 0.216-inch injectors and a larger...
Piston assemblies and turbocharger from a 130hp 1.9 TDI (AVF) engine, and a T5.
Intercoolers were installed.

Since the components are quite specifically mixed, we initially didn't want to do (or have done) any chip tuning.

As expected (and desired), the increased injection volume results in more power, but the engine also produces a lot of black smoke under load/part load.
because the boost pressure is too low, and the injected fuel cannot be properly combusted.

I have read articles by Ulf and here on the forum, and it seems that there is a possibility...
consists of increasing the boost pressure by modifying the signal from the intake manifold pressure sensor.
"...is distorted before it reaches the engine control unit. This is achieved by reducing the measured signal."
As I understand it, a lower boost pressure value is being transmitted to the MSG.
The engine control unit (ECU) then increases the turbocharger boost pressure accordingly.

This distortion can be achieved either using diodes or resistors, and that's where opinions diverge...

In his article, Ulf writes that, unlike the internal pressure sensor, such as the AFN type, there are no reliable values available for modifying the external sensor.
Another user wrote that this signal distortion could be achieved using diodes, while another user advises against using diodes, calling them completely unsuitable (AKN tuning), and states that adding a 100-ohm resistor in the signal line results in a reduction of the measured boost pressure by 135 mbar.

Since the AKN is a V6 TDI engine and the MAP sensor only has 3 pins, I'm hesitant to simply apply this finding to a four-cylinder engine.

My question is whether someone can provide me with a guideline regarding the sizing of the components, and whether I should use diodes (if so, which ones?) or resistors.

Another question would be what actually happens when the sensor reaches its measurement limit. For example, the AHF sensor has a 250 kPa version installed, which means it can detect and convert a pressure of approximately 1.5 bar (above atmospheric pressure) into a signal.

I am fully aware of the risk of overboost and the fact that the engine management system (MSG) may not be able to switch to emergency mode quickly enough, which could lead to damage to the turbocharger. Therefore, I will definitely use a boost pressure gauge! Furthermore, I also know that this method cannot replace a properly calibrated map!

I still hope that you can give me some advice.

Best regards

Deus Violentia wrote:

to increase the boost pressure by increasing the signal of the intake manifold pressure sensor. "...is distorted before it reaches the engine control unit. This is achieved by reducing the measured signal." As I understand it, a lower boost pressure value is being transmitted to the MSG. The engine control unit (ECU) then increases the turbocharger boost pressure accordingly. This distortion can be achieved either using diodes or resistors, and that's where opinions differ... In his article, Ulf writes that, unlike the internal pressure sensor, such as the AFN type, there are no reliable values available for modifying the external sensor. Another user wrote that this signal distortion could be achieved using diodes, while another advises against using diodes, considering them completely unsuitable (AKN tuning), and states that an additional 100 Ohm resistor in the signal line results in a reduction of the measured boost pressure by 135 mbar...

Hi Deus,

Since you seem to be approaching the sensor modification with some consideration, here's my non-binding tip:

The distortion of the LD signal caused by a diode is difficult to calculate because the sensor load is minimal due to the input impedance of the measurement signal generator (MSG), and the actual behavior of the diode therefore fluctuates between that of a resistor and a theoretical diode (with a constant voltage drop of 0.7 V). Furthermore, it is also significantly dependent on the current depletion layer temperature.
Therefore, the resistance method is more predictable.
I would start by measuring the input impedance of the MSG (Impedance) at the LD pin with respect to ground. As a first step, I would insert a resistor into the signal line, with a value of 5-10% of the impedance, as close as possible to the MSG. This is to minimize the length of the "high-impedance" signal path behind the fake resistor, which acts as a particularly sensitive antenna for various interference signals.

Then, take a cautious test drive, always keeping an eye on the LDA (lambda-dependent addressing), and as long as it's not behaving erratically, you can gradually increase the power output.

In addition to the emergency mode function, which may be deactivated in certain cases (*), and the warning about potentially high LD values, please note that depending on the data available, the relationship between the sensor values for LD and ambient pressure can also be checked when the ignition is turned on. If there is a significant deviation, an error will be triggered, and the engine may be in emergency mode before you even start driving.


*) Example: The programmed emergency shutdown threshold is 2.4 bar, and the sensor's measurement range ends at 2.5 bar. Now, the LD (presumably "lower detection limit") is artificially increased by 0.2 bar using a sensor fake.
If the LD (likely referring to a pressure value) then increases, for example, to 3 bar, the sensor sends its maximum possible value of 2.5 bar through the cable, but only 2.3 bar actually reach the MSG (likely a control module), resulting in no limp-home mode activation despite the 3 bar LD.

Okay, okay , I was initially thinking of an increase of 0.2 bar. I'll measure what you're suggesting.

As far as I've read, the pin configuration for the boost pressure/charge air temperature sensor is as follows:

- Pin 1: Ground (0 V)
- Pin 2: NTC charge air temperature sensor connection from the control unit.
- Pin 3 provides +5V power for the boost pressure sensor.
- Pin 4: Output signal (voltage) - Turbocharger pressure sensor.

I need to connect the resistor to pin 4, right? Also, does the characteristic curve of such a sensor typically remain linear from the lower to the upper measurement range?

"Unlike a diode, which, as you mentioned, has a specific characteristic curve, I always reduce the output voltage by the same amount using a resistor."

I don't quite understand why I need to measure the input impedance at the MSG and then adjust the value based on that measurement...

In my opinion, it would be relevant to start with...
What is the minimum value of the sensor (approximately 0.4 bar overpressure or?) and within what range does the voltage change until the sensor reaches its measurement limit (so, for a 250 kPa sensor, minus the atmospheric pressure, approximately 1.5 bar)?

Knowing this, one can calculate the desired pressure change, i.e., the resistance value that must be used to achieve a reduction on the sensor line by precisely that amount. This can then result in something like "100 ohms corresponds to 135 mbar," or a similar relationship.

Based on this line of reasoning, I don't understand what this has to do with the impedance related to the MSG.

Can the sensor voltage be read out through the measurement blocks? If so, I could simply log the voltage and the target boost pressure and see how they are related, right?

Best regards

Now that I have successfully passed my "Blaumann" exam, I would like to request that someone move my thread to the correct section.

Thank you very much!

Hello,

I would caution against DIY ideas like the ones you are asking about here.
You can try to achieve a slightly higher LD (Light Dependent Resistor) value in conjunction with a 10-cent tuning using a voltage divider or a diode, but your modification is a significant change that cannot be controlled through sensor manipulation alone.

Ulf has written extensively about the problems of sensor manipulation. Due to the improperly adjusted turbocharger boost control and the additional fuel injection, there will be significant overshoots that the engine control unit (ECU) does not detect. This essentially predetermines turbocharger failure.

One can only speculate about the motor's load behavior when the pump voltage is not properly adjusted.
Everything is not great .

My tip:
Find a tuner who can properly calibrate the engine to match this collection of parts. The cost of the first failing dual-mass flywheel or the first defective turbocharger is higher than the cost of having everything properly calibrated once.

Not to mention the driving pleasure.

Best regards, Jochen.

Hehe... We have enough chargers here in stock, and as I mentioned at the beginning, I know that's not a great thing...

But I still want to try it because I simply want to see how everything changes. I am fully aware that I am completely bypassing the protective mechanisms of the MSG with something like this.

As I said, I'm risking damage to the charger, and I'm aware of that... I'm not expecting great results from this action. I just find the possibility very interesting and want to try it out. Even a poorly executed attempt can be insightful.

And if one is aware of the consequences that such an intervention has, one can, I think, keep the risk within limits, for example, by manually measuring the boost pressure.

And if one is aware of the consequences that such an intervention has, one can, for example, keep the risk within limits by manually measuring the boost pressure, I think.

I don't agree with that, because you need to adjust the control behavior accordingly. Simply reducing the measured LD value so that it can be detected by the MSG and the desired height is achieved doesn't necessarily improve the control behavior.

The MSG (presumably a control module) alters the control behavior depending on the difference between the target and actual load values. This completely confuses the system and also increases the volume of exhaust gas, which drives the turbocharger.

I think that the engine, as it were , somehow , is running, but one certainly cannot talk about its driving characteristics or durability...

Best regards, Jochen.

Deus Violentia wrote:

1) Is the characteristic curve of such a sensor actually linear from the lower to the upper measurement range? 2) "Unlike a diode, which, as you mentioned, has a specific characteristic curve, I always reduce the output voltage by the same amount using a resistor." 3) I don't quite understand why I need to measure the input impedance at the MSG and then adjust the value based on that measurement... 4) In my opinion, it would be relevant to start with... What is the minimum value of the sensor (approximately 0.4 bar overpressure or?) and within what range does the voltage change until the sensor reaches its measurement limit (so, for a 250 kPa sensor, minus the atmospheric pressure, approximately 1.5 bar)? 5) Based on this line of thought, I don't know what this has to do with the impedance related to the MSG.

I appreciate your enthusiasm for DIY projects, but I would advise you to consider more than just a boost pressure falsification for such extensive hardware modifications. Are you aware that if your turbocharger fails, having a spare turbocharger on hand won't be much use? Depending on the defect, the pieces can end up in the engine oil or catalytic converter, requiring replacement. In the worst case, they could even damage the engine itself, leading to a complete failure.

But those who refuse to listen will have to experience it firsthand, and if you're willing to do that, I'm at least willing to correct your misguided beliefs so that you have a chance to truly understand.

1) Yes, relatively linear.
"With a resistor, you only reduce the voltage by a defined amount when a defined current flows! However, that is not the case here (resistor divider with a variable sensor output voltage)."
3) The MSG has a termination resistor connected to the ground at the LD sensor input. This acts as a voltage divider. Once you know the internal resistance of the MSG, you can determine the current flowing into the MSG (which is proportional to the sensor voltage).
4) I don't have the exact characteristic curve. Roughly speaking, at 0 bar (absolute vacuum), it should output around 0 V, and at 2.5 bar (which is 1.5 bar overpressure), it should output around 5 V. In reality, the actual value is likely to be between 0.5 and 4.5 V.
5) See above. The sensor output provides a constant voltage. After the sensor output, you have two resistors in series (or a diode and a resistor in series). The first resistor (or diode) is now connected by you. The second resistor is located within the MSG (Microcontroller/Module/System) between the input and ground. It determines the current flow. The MSG measures a very high impedance at the sensor input (apart from the internal pull-down resistor).

If you choose the external resistor to be inserted, as Ulf describes, at approximately 10% of the MSG pull-down value, you will achieve a distortion of approximately 10% of the current absolute pressure. (100/110 = 9.1%). With an LD of approximately 1 bar (2 bar absolute), this translates to an additional pressure of 0.18 bar.

Regards,
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

@jochen: Hmm, I hadn't thought about the setpoint and actual value regulation until now, and you're right, that's not a positive thing...

I'll see how badly the engine is running...

@guste: Yes, the risk is high. Thank you for the explanation!

Deus Violentia wrote:

I'll see how badly the engine is running...

I'm generally curious about the results and promise not to say "I told you so."

ulf wrote:

I would be interested in the results out of general curiosity, and I promise not to reveal any "inside information"

.
In the first part of the statement, I agree with Ulf, but regarding the second part, I'm not entirely sure yet .

Okay, let's see if I can be productive despite (understandable) criticism... I really hope so .
More opinions are always welcome .

Since I have just successfully passed my 'Blaumann' exam, I would like to request that someone move my thread to the correct section.

Thank you very much!

I'm glad you managed it, but it wasn't unexpected .

You're welcome!


Best regards, Alex.

Here are the graphs for the boost pressure sensor and the corresponding boost pressure temperature sensor.

Boost pressure:
http://www.geocities.com/tech4tdi/pages/pictures/intake_press_sensor_graph.png

LDTemp:
http://www.geocities.com/tech4tdi/pages/pictures/intake_temp_sensor_graph.png


And here is the entire page (in English):
http://www.geocities.com/tech4tdi/pages/map.html

I hope this helps you.
Best regards,

@kerosin: Great, thank you very much!

If anyone is interested...
I've now increased the boost pressure by adjusting a potentiometer (volume control).
"Under full load, it initially reaches 1.5 bar, then stabilizes at 1.3 bar. However, under continuous full load, it drops to 1.2 bar after some time... I personally think this is good, as it prevents the engine from overheating too quickly during highway driving."
Well... I've already driven over 5000 km without any problems.
According to the VAG-Com diagnostic tool, the vehicle has a faulty boost pressure reading at idle, showing approximately 850 mbar. Under actual load, the boost pressure is around 2000 mbar, but the engine control unit (ECU) believes it to be only about 1950 mbar when the actual boost pressure reaches 2300 mbar.
The voltage at the sensor was initially 2.07V (no load), and after adjusting with a resistor, it was 1.80V... I think. It's been a while since I adjusted it, so I'd have to measure it again if anyone is interested.