I recently purchased a Lufi XS unit, wanted to use it as boost gauge mainly and displaying water, oil temp ...etc. However it's not displaying properly on boost gauge mode, it seems that when I cold start the car, the unit will register vacuum at idle (~20 IN-Hg) after a few minutes of warming up the car, as soon as I step on the gas pedal to get going, the gauge pointer would just get stuck right below 0.... it will still display boost PSI but just not vacuum.....

Does anyone use this unit who experience the same? what's your work around?

Thanks in advance.

 

What year is your car? 2011+ N18 engines operate in such manner. During cold start, the engine will pull vacuum in the manifold to help with cold start emissions. After warm up, the controls will open the throttle plate 100% and modulate the intake cam lift for load control. This type of control will cause the manifold to see zero vacuum-boost during idle and cruise operation. I have a mechanical boost gauge in my car, and have been able to verify this operation.

 

yes i have a 2012 cooper s… oh so even a mechanical boost gauge wouldn’t display vacuum reading at idle???

 

Nope, that's how the engine and controls are designed. You'll only get vacuum in the manifold under very specific circumstances.

 

Thank you so much Nik, this is very helpful.