Fuel pump running when opening the driver's door - what's the deal?

Hello,

the above-mentioned. Both my Polo (2.0 TSI) and my partner's Rapid (1.4 TSI) exhibited this behavior.
You can disable it with VCDS, and since then, the Polo has started just as readily as before.
I disabled it on my Rapid yesterday, and so far, there have been no side effects.

Therefore, my question is: What is the purpose of the pump running for approximately 1 second when the driver's door is opened?

To ensure that the fuel system is properly bled before the engine is started?

Some diesel vehicles may also start the preheating process at this point.

Best regards, Rainer.

dieselschrauber wrote:

To ensure that the fuel system is bled before the engine is started?

Sure, here's the translation:

"Supplement:"
... And to remove air bubbles from the system, especially in hot weather.

This is a major issue, especially with direct injection engines.
Actually, the issue of vapor lock was supposed to be a thing of the past since carburetors were phased out, but it's back.

dieselschrauber wrote:

To ensure that the fuel system is bled before the engine is started? Some diesel vehicles start preheating at that point.

Hmm... Pre-heating is always a necessary starting preparation when the engine block is very cold, but bleeding a sealed and non-empty fuel system is actually not required.
Unless you're experiencing air bubble problems (thanks, @Bertil), then flushing the system with cold fuel from the tank makes perfect sense.
Let's see if our TSIs will start acting up with unsolvable hot-start issues during the peak of summer... then I can reactivate the function again.

"However, I'm not entirely convinced by the explanation involving steam bubbles, because both the BNStG systems (from Polo and Rapid) apparently have a timer that suppresses the second and subsequent pump cycles if the door is opened multiple times within x minutes."
According to my feeling , new steam bubbles would form more quickly after a brief ~1 second flush of the hot fuel system , than the next cycle of door opening and pump operation would allow.

Quote:

Based on my feeling icon_redface.gif, after a short ~1 second flush of the hot fuel system, new steam bubbles would form faster than the next door opening and pump cycle allows icon_eek.gif

My feeling is that the door isn't opened every 2 minutes, but rather you get in, start the engine, and drive away.
Possibly, this time is sufficient; therefore, open the door slightly (1. pump start) and initiate the start sequence (2. The "pump priming" function is specifically designed to eliminate air bubbles and restore fuel pressure.

Quote:

Possibly, this time is sufficient; therefore, open the door (1. pump start) and begin the process (2. The pump's priming function is specifically designed to remove air bubbles and restore fuel pressure.

There might be a pressure relief valve. If the system has initial pressure, then it won't need any further "bleeding" cycles.

vwSchrauber wrote:

... There might be a pressure-holding valve; if the system already has pre-pressure, then it doesn't need another "bleeding" cycle.

The system even measures the pressure and uses this to control the operation of the pumps.

I would need some more information regarding the boiling behavior of (standard) gasoline, specifically a diagram or table showing the temperature at which vapor bubble formation begins and the corresponding pressure.

In my own words, the technical problem is: "What pressure must the gasoline be at when it reaches the injection system in order to avoid vapor lock?"
I know that the necessary pressure depends on the gasoline temperature. However, I can't find a diagram anywhere on the internet that shows something like "pressure-dependent boiling point of automotive gasoline" .

http://www.chemieonline.de/forum/archive/index.php/t-145580.html

Here you can find something for individual components.
http://ddbonline.ddbst.com/AntoineCalculation/AntoineCalculationCGI.exe

Take the most volatile component of gasoline, and you're on the safe side.

Thank you, @Bertil.

The trigger for my question was the overheating of the fuel pump control unit (ECU) in a 2.0L TFSI engine that had been chipped. This resulted in an engine malfunction due to minimal residual fuel pressure before the fuel rail, with a calculated temperature of around 80°C.
The fuel pump solenoids (StGe) seem to be already operating at their maximum capacity with the standard performance of the more powerful 2.0-liter EA113 engines, and they tend to fail more often, especially during the summer, when the engines are tuned.
By lowering the desired low pressure, one could alleviate the stress on them somewhat, but then the risk of steam bubble formation increases.
I wanted to get a rough idea of how much reserve is built into the programmed pressure profile, so I put together something based on information from Bertil's two links ("The boiling point of the low-boiling hydrocarbon pentane increases from 36 °C at normal pressure to approximately 126 °C at 10 bar") and the programmed setpoint for the low pressure profile of the MED9.1. According to this, the programmed pressure reserve decreases as the temperature increases (at 6.6 bar, a return valve in the line-mounted pre-filter opens).
Since the Siedekurvenverlauf (boiling point curve) of pentane between 36 and 126°C is only an assumption, I unfortunately don't have much more information to determine how much the target low pressure could be reduced .

By ensuring that only the correct fuel type is used in the vehicles, you can potentially save around 10,000 [currency unit]. The pressure is naturally set very high by the OEM, because the pump/control unit can be pushed to its limits.

Usually, things only start to go wrong during the tuning process. It's also worth noting that, occasionally, the series experiences issues with the pump control unit.