Boost Pressure Sensor Kit: Speedbuster I/S/T

Hello,

Here's a short testimonial:

After my mass airflow sensor (MAF) failed in my Audi A3 (75,000 km), I quickly replaced it with a diode that has a voltage drop of 0.7V. This works perfectly on my car; VAG-COM consistently reports a value of 1275 mg/stroke.
I encountered a problem where my Speed Buster device was no longer receiving a signal. It's supposed to interpret the Mass Air Flow (MAF) sensor feedback signal and send it to the Engine Control Module (ECM). This signal varies between approximately 2 and 4 volts, depending on the load.

Since I was already connected to the pressure sensor, I used that signal to control the on/off threshold of the device.
Dabei ist mir folgendes aufgefallen: Die Spannung vom MAP-Sensor beträgt gegen Fahrzeug-Masse im Leerlauf ca. 1.8 Volt (4.2 Volt bei max. Ladedruck). Gegen den LMM-Kontakt der Box beträgt die Spannung aber nur 0.9 Volt im Leerlauf (2 Volt bei max. L(printed advertisement).
For this reason, I was a bit unsure how the MAP sensor would react when connected to the adapter. However, continuously logging the pressure reported to the engine control unit (ECU) showed no change compared to the previous state. Furthermore, approximately 4 microamps are flowing from the MAP sensor to the adapter, so there's likely no overload of the sensor.

The settings on the box had to be adjusted: I needed to turn it back approximately 5 rotations, and T needed to be turned forward about 2 rotations, compared to a setting that, when connected to the mass airflow sensor (MAF), adds extra fuel injection starting at around 2000 rpm.

The device now noticeably activates only when the boost pressure reaches approximately 1900 mbar (absolute).
For me, this is perfectly fine because I only want the additional fuel injection to kick in when the engine is running at full load.

It's also interesting that with the spindle I, the difference between a true fog generator and one without any additional power lies within a range of about 1 revolution.
When connecting to the mass airflow sensor (MAF), you need to adjust it over more than 5 rotations.

Let's see how it goes from here. I wouldn't recommend this method generally just yet, because you often only notice the inconveniences over time.

Okay, here are the functions of the I/S/T potentiometer knobs on the unit:
"I limits the maximum additional injection amount."
"T controls the threshold at which point an additional amount of fuel injection is released."
It defines a constant additional fuel injection volume regardless of the signal (whether it's from the mass airflow sensor or, in my case, the manifold absolute pressure sensor).

What do electronics experts say about the lower voltage measured between the MAP signal and the box's mass airflow sensor (MAF) input, compared to the voltage measured between the MAP signal and the vehicle's ground? Could this lead to problems in the long term?

Best regards, Georg.

Georg_G wrote:

Dabei ist mir folgendes aufgefallen: Die Spannung vom MAP-Sensor beträgt gegen Fahrzeug-Masse im Leerlauf ca. 1.8 Volt (4.2 Volt bei max. Ladedruck). Gegen den LMM-Kontakt der Box beträgt die Spannung aber nur 0.9 Volt im Leerlauf (2 Volt bei max. L(printed advertisement). Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. What do electronics professionals think about the lower voltage measured between the MAP signal and the box's MAF sensor input, compared to the MAP signal against vehicle ground?

Could this lead to long-term problems?
Hi Georg,

I'm not quite sure what to make of your measurements yet.

MAP -> Mass = 1.8 - 4.2 V results in a sensor voltage swing of 2.4 V during operation.

MAP -> Box = 0.9 - 2 V results in a sensor voltage swing of 1.1 V.

That would mean that either the sensor itself is changing its voltage output, or its high impedance is reducing the measured value (which is my assumption).

To clarify the issue, it would be helpful to measure the voltage of the box's input relative to ground.
What type of device did you use to measure the voltages?

If my assumption proves to be correct, and the voltage measured between the box's input and ground is not measurable, then what appears to be a "problem" seems like complete normalcy to me. }

Is the LMM input actually the only control input for your device?

Hello Ulf,

I'm measuring 0.7 volts between the LMM input of the control unit and the vehicle mass, with the engine off/ignition on only.

The LMM input is the only obvious control input for the box. However, I suspect that the box also only allows the extra injection amount, which is set via the potentiometer "S", to be activated when the control voltage of the actuator in the pump cable harness exceeds a certain threshold. This would function similarly to the 10ct tuning method using a diode and resistor connected in parallel to pin 2 / pin 3.
I suspect this because manipulating the quantity setting signal via "S" would likely cause excessive jolting when the system is idle. (This is precisely the effect observed when a resistance of approximately 800 ohms is placed between pins 2 and 3 of the pump cable harness).
This stutter actually doesn't occur with the letter "S," except in cases of extreme misconfiguration.

What do you think about controlling the box using the boost pressure signal?
Perhaps I should compare the mass airflow sensor (MAF) signal to vehicle ground with the MAF signal to the MAF input of the control unit. If there's a similar voltage drop there as well, then "it probably behaves like that by design."

I took the measurement using a cheap digital multimeter.

Regards,
George.

Georg_G wrote:

What do you think about controlling the box using the boost pressure signal?

This prevents you from achieving a performance boost that varies with engine speed, particularly at higher RPMs.

Quote:

Maybe I should compare the MAF signal to vehicle ground with the MAF signal to the box's MAF input. If there's a similar voltage drop there as well, then "

"that's probably normal."}
IMO, it will definitely be like that...