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That pump is used to increase the Diesel fuel pressure to about 6 bar and has the vacuum pump built in.....but...again...needs oil.
The old type vacuum pump from the 1.9 TDI engines is nice....but needs oil also...and is driven by the cam.
VEMS can use the ECU map sensor to control when the pump will start/stop operating. It will get more complicated if another sensor needs to be mounted inline for VEMS to control and i think its not necessary.
The electric pump will only be required if vaccum is above a certain level which is not enoughto pressurise the servo OR durring positive pressure, so that the servo is always under vaccum. Hence my thinking that since servo wont be damaged in any way if it always sees vacuum(that's whats happening in non boosted cars anyway), the electric pump can be put to work only on those specific situations. Say for example from 90kpa (100kpa being 0 boost), and above. So whenever you are accelerating, even though the servo may still have enough pressure, the electric pump will switch on.
My concern is, if the electric pump will fail prematurely by working this way or not.
Is not ok to use the map sensor from the ecu to control this...because, even iff you are under 2 bar off boost, the brake booster will hold the vacuum until the brake pedal is pressed. So is no need to operate the pump in this situation. You need another map sensor to control the brake booster vacuum only and control the pump. My ideea
Dont know iff Vems has another input and output for this...the ecuation is simple though.
But..again...i used my car without these complicated things without issues.
im not sure how this would connect to the system though, as it is meant to be connected to the vaccum servo alone(?)
i presume the switch senses when the vaccum is above the 20inch and switches off, while it turns on again when it is below that. However that means that again it will work continuesly no matter if the servo is already fully pressurised.
So ideally you need a sensor that tells you that the servo is fully loaded, and doesnt need any more vaccum to get pressurised.
I do have some problem calculating the figures correctly, as vaccum is expressed in various different ways. For example in kpa figures, the lower the figure, the higher the vaccum, but when you put that into the online calculators, you dont get the desired equivalents! haha
here is a pdf which explains the working systems of 2 audi electric pumps.
apparently there is an open and a closed loop system and the open system seems to be similar to what i mentioned above, being able to handle the pump with VEMS. It looks as though that on the open loop, the ECU 'calculates' the pressure in the servo indirectly, by taking into account the TPS, Load(ie MAP), brake light and engine speed(rpm). With that it enables/disables the pump.
So all that can be applied in VEMS but with certain assumptions. The only thing that VEMS cannot 'see' is the brake light. So if you define what rpm/pressure/TPS position you want the pump to work in, it should be able to at least cover for the unlikely even of running out of vaccum on the servo unit at all times.
At my engine i had ~-0.5 bar at idle. I would calibrate the switch to open the pump circuit when the vacuum is at -0.5 bar at the booster. In the event that the vacuum is going less then -0.5.....-0.4-0.3. The switch is closing the circuit and the pump starts until the -0.5 bar is reached.
here is a pdf which explains the working systems of 2 audi electric pumps.
apparently there is an open and a closed loop system and the open system seems to be similar to what i mentioned above, being able to handle the pump with VEMS. It looks as though that on the open loop, the ECU 'calculates' the pressure in the servo indirectly, by taking into account the TPS, Load(ie MAP), brake light and engine speed(rpm). With that it enables/disables the pump.
So all that can be applied in VEMS but with certain assumptions. The only thing that VEMS cannot 'see' is the brake light. So if you define what rpm/pressure/TPS position you want the pump to work in, it should be able to at least cover for the unlikely even of running out of vaccum on the servo unit at all times.
These sistems are used on cars with automatic gearboxes mostly...i think is too complicated...at least the closed loop one.... The open loop is more easy....
apparently, even the new cars dont always use a sensor to calculate the excact pressure that lies in the servo. They assume it by other features (open loop).
in the closed loop situation, i dont think VEMS can be able to control that extra sensor to define when the pump should open and close, but since the open loop is already adapted, it should be ok to run.
I think all that is needed is a robust one way valve from manifold to a vacuum reservoir bottle with a connection from there to the vacuum servo. Depending on size of vac reservoir you should have enough reserves for servo assistance for left foot braking... which you aren't going to be doing often unless you are the Stig on maximum attack on a closed road somewhere !
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