[Volkom]

Hi all,
I'm wondering if anyone has any readings for what vacuum at idle should be for the N20 via scan tool. If not for me then for future members wondering the same thing...

I have access to ISTA but the live data absolutely blows, so i'm using a wifi scan tool and Torque with RealTimeCharts to log everything.

My vacuum/boost gauge sensor reads -0.8 PSI (-1.6 in Hg) at idle.

This seems extremely low, and i'm wondering if the PID reads incorrectly with my scan tool, my sensor is bad, or if i have a vacuum leak.

I smoke tested the intake, found no leaks- will verify with an analog vacuum gauge this week and update accordingly.

(EDIT: See posts below, this MAP reading is completely valid for this engine)

[ScottSmith]

Valvetronic cars don't necessarily build a lot of vacuum in the manifold; instead they only build vacuum in the cylinder itself. I can't find a reference to it, but I read that the throttle is only used to maintain a slight vacuum. It might be for PCV purposes but I don't remember.

There's a separate vacuum pump to aid the brake booster and wastegate (on cars without electronic wastegates).

[Volkom]

Thanks for the insight- i didn't know that.
I measured the vacuum line that goes into the pressure converter for the pneumatic wastegate with a 25 dollar gauge from Harbor Freight:

-12 to 14 psi (-25 to 30 in HG) Increasing over the course of ~5 seconds after i plugged it until it reached the upper limit.

I wasn't able to get a good reading of anything connected to the intake manifold because the connectors didn't fit perfectly but i'll try to get one maybe tomorrow.

Looks like my vacuum is good to the turbo, but i haven't verified the actual MAP sensor readings via ISTA.
I smoke tested the intake via the same line a few days ago and smoke was getting to the entire system- logically i presume that this means the vacuum everywhere should be good as well but i'm not 100% sure.

I'm confident my lean air condition (not mentioned here, separate thing) is not due to a vacuum issue now, but rather due to having a DME that used EU5 injectors connected to a new engine that has EU6 injectors installed. If someone has this same issue in the future, do not hesitate to DM me if I haven't updated the post.

[ScottSmith]

DME needs to be recoded whenever you swap injectors. There's a 3 digit number on the side of the injector that needs to be inputted into whatever programming tool.

Vacuum to turbo has nothing to do with manifold. It's driven by a pump on the back of one of the cams. https://www.realoem.com/bmw/enUS/sho...diagId=11_4786

[Volkom]

EU6 injectors with a DME that expects EU5 is apparently still incompatible regardless of whether you have calibrated them- i have performed the reprogramming.

There's no easy line to test vacuum going to manifold with then, all the fittings are solid and rather inflexible unfortunately. Going to have to make a rubber cone or something idk.


EDIT:

Further research suggests 50 millibar vacuum is normal for these engines, which is much lower than regular engines as @ScottSmith elucidated earlier.
Per an article linked here:

Thus, if the idle quality is poor but a scan tool displays an eccentric shaft position of less than 30 degrees* of rotation while the manifold vacuum is at about 50 millibars, the engine is running in valve lift control mode.

So, 50 millibar vacuum is equal to -0.725 psi, indicating my idle MAP reading was valid. Note that in the article linked above it is mentioned that the vehicle needs to be under specific conditions for this vacuum condition to be as it is.