VVEL Question on Intake Manifold Pressure

SonicVQ · 01-07-2016, 10:31 PM

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?

SouthArk370Z · 01-08-2016, 08:08 AM

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

BGTV8 · 01-08-2016, 02:36 PM

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

SonicVQ · 01-08-2016, 07:34 PM

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.

SouthArk370Z · 01-08-2016, 09:20 PM

Quote:

Originally Posted by SonicVQ

... 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.

SonicVQ · 03-05-2016, 09:56 PM

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.

01-07-2016, 10:31 PM	#1 (permalink)
SonicVQ Base Member Join Date: Jan 2016 Location: Ontario Posts: 230 Drives: G37 Sport Rep Power: 6720	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? Last edited by SonicVQ; 01-07-2016 at 10:42 PM.

01-08-2016, 08:08 AM	#2 (permalink)
SouthArk370Z Premium Member Join Date: Nov 2010 Location: South Arkansas Posts: 8,435 Drives: 2014 Challenger Rep Power: 324198	The throttle plates are still moving around. They don't just fly wide open and stay there. __________________ Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

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01-08-2016, 02:36 PM	#3 (permalink)
BGTV8 A True Z Fanatic Join Date: Dec 2009 Location: 03350 Australia Posts: 1,514 Drives: 09 Nissan 370Z M6 Rep Power: 39973	The engine is throttled by a combination of throttle plate angle AND valve lift.

01-08-2016, 07:34 PM	#4 (permalink)
SonicVQ Base Member Join Date: Jan 2016 Location: Ontario Posts: 230 Drives: G37 Sport Rep Power: 6720	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.