VVEL Question on Intake Manifold Pressure
 

From what I have read with the VVEL system, the throttle bodies are not used once the engine is running.

If so:
(1) Where does the vacuum for the brake booster come from?
(2) Why does my MAP sensor show 22 inches/Hg vacuum at idle?

What is going on?

The throttle plates are still moving around. They don't just fly wide open and stay there.

The engine is throttled by a combination of throttle plate angle AND valve lift.

Thanks for the info. After some more searching I found this:

"The engine's speed and output is largely managed by ECU control of the intake valves, not the throttle bodies. By not having the restriction of the throttle blade at partial throttle, fuel wasting pumping loss is reduced.

The engine does have dual drive by wire throttle bodies but they are used only for brake booster vacuum control and quick acting modulation for traction control. Otherwise the throttles are wide open most of the time."

(source: ***************************************/tabid/57/articleType/ArticleView/articleId/14/PageID/62/Nissan-370Z-Review-Engine-VQ37VHR.aspx)
interesting, can't link to own site...
Try the370 dot com /MagazineArticles/tabid/57/articleType/ArticleView/articleId/14/PageID/62/Nissan-370Z-Review-Engine-VQ37VHR.aspx

I guess the MAP PID is being modified by the OBD-2 output to a "expected" value and not actual. If I am 20% throttle, constant speed, there should be none to little intake manifold vacuum - but the MAP PID shows ~15" vacuum.

The TPS value is faked but I don't recall MAP being fudged. FSM should have details.

Update:
After monitoring the intake manifold vacuum and throttle position, the TB does close when you lift off the accelerator. It opens when the throttle position is greater than about 13%. This keeps enough vacuum for the brake booster and for the mode $06 evap tests.


http://www.the370z.com/attachment.ph...1&d=1457232526