Report on increasing boost pressure

Hello,

Several weeks ago, I started a thread about the pin configuration of the combination connector for the boost pressure/charge air temperature sensor on the newer 1.9 TDI engines.

Today, I finally increased the boost pressure. Here's how I proceeded:

"The entire cable bundle was completely severed. Four-pin connectors were soldered on, and corresponding pin headers were attached to the breadboard. Initially, the contacts on the circuit board were connected in a 1:1 fashion, meaning no boost pressure adjustment was implemented yet." I tapped into the boost pressure signal, which is a voltage ranging from 0 to 4.65V, where 1.85V represents idle and 3.75V indicates the regulated maximum boost pressure. I read this signal with a digital multimeter inside the vehicle while driving.
Aggressive drivers who were speeding were, for the most part, not easily provoked; max. The measured value was 3.95 volts, which corresponds to approximately 1.12 bar.
"Using these values as a reference, I then connected a Schottky diode (a standard type, I don't recall the exact model number) in series with the output signal. This time, the circuit was designed so that I could measure the boost pressure signal voltage both before and after the diode." The diode's voltage drop was 0.1V when idle; it was also approximately 0.1V during operation.
I was actually able to further adjust my tuning box without noticeable black smoke emissions. (However, this is a very subjective matter, and I've noticed that the black smoke behavior (triple double s) somehow depends on the day's conditions.
The change should theoretically only increase the pressure by 0.05 bar. That's a joke. However, the adjustment behavior has changed significantly. Now, when accelerating abruptly from 2500 rpm, I'm seeing overshoots up to 4.2V. I also have the impression that the gas intake has become more spontaneous.

That's all I'll say about that for now...

Okay, here's the translation:

Now, my questions:

Why is the voltage drop only 0.1V? Schottky diodes should have a forward voltage of 0.3V, right?
How much pressure can my loader javascript:emoticon('') handle?
Laughing?

Best regards, Georg.

...

"How exactly can I adjust the VTG (Variable Turbine Geometry) to make the control behavior more stable and eliminate any overshoot in the boost pressure?"

Georg.

Hi Georg,

The diodes I am familiar with, including Schottky diodes, exhibit a resistance-like characteristic in the region of minimal current.
If your engine control unit (ECU) has a high input impedance (for the boost pressure sensor), very little current will flow through the diode, resulting in a minimal voltage drop.

If the diode current, which corresponds to the voltage drop, increases along with the measuring voltage (boost pressure), this can certainly explain the significant overshoots, because the boost pressure information received by the engine control unit increases more slowly than the actual boost pressure.

Solution: Connect a resistor between the diode and ground, ensuring that the sensor is not overloaded.
This also increases the constant voltage drop across the diode. I would start with 100kΩ and gradually decrease the resistance if needed.


You can adjust the overtravel (Überschwinger) using the VTG (Variable Travel Gauge). To do this, carefully increase the length of the threaded rod in increments of approximately 0.5 revolutions.

Hello Ulf,

Thank you for your reply.

I connected a potentiometer (100K to 0K) between the diode and GND, as you described. Then, I measured the voltage drop while decreasing the resistance from 100K. Starting at 20K, the voltage drop increases. Below 7K, a sudden drop to 0V is measured between GND and the feedback signal, indicating that the sensor's output current has likely failed.

Okay, so I installed a fixed resistor with a value of 10K ohms, which allows me to now precisely set a constant full-load pressure of 4.95 volts, which is approximately 1.1 bar. And with the tuning box cranked up, there's absolutely no smoke anymore. The only problem is the overpressure; in some places, it's already reaching around 1.25 bar.

Are these 1.25 bar short-term and 1.1 bar long-term already on the rather shorter side of a (hopefully long) charger lifespan?

The driving behavior is like the standard model, except for a wild buffalo under the hood .

Best regards, Georg.

Georg_G wrote:

Are these 1.25 bar short-term and 1.1 bar long-term already on the rather shorter side of a (hopefully long) charger lifespan? The driving experience is like the standard model, except for a wild buffalo under the hood

.

Hi Georg,

I don't consider 1.25 bar for occasional fractions of a second to be critical.
According to several people whose expertise I trust, a constant pressure of 1.1 bar, even at higher engine speeds, is still acceptable; however, significantly higher pressures may likely cause the turbocharger to "degrade" more quickly.

Having fun with the buffalo, right ?