About the intake manifold tuning control system
06-10-2003, 11:15 AM
#1
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About the intake manifold tuning control system
This is what I found (don't know if it adds anything to what's already been said):
At low RPM vacuum is applied to the change-over valve actuator, the change-over valve in the manifold is closed and air has to travel the longer path to improve torque at low speed.
At a a preset RPM (which one?), the ECU de-energizes the control solenoid, vacuum is vented from the actuator, and the change-over valve opens. Air travels now the shorter path in the intake manifold.
According to my manual, the actuator rod should start moving when the RPM exceed 4500.
At low RPM vacuum is applied to the change-over valve actuator, the change-over valve in the manifold is closed and air has to travel the longer path to improve torque at low speed.
At a a preset RPM (which one?), the ECU de-energizes the control solenoid, vacuum is vented from the actuator, and the change-over valve opens. Air travels now the shorter path in the intake manifold.
According to my manual, the actuator rod should start moving when the RPM exceed 4500.
06-10-2003, 03:25 PM
#2
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Something like this...
<center><img src="http://pictureposter.audiworld.com/18363/engine_air.jpg"></center><p>Never feel the changeover myself, I always feel the car seems lethargic over 4000rpm when you pass the peak torque point around 3000rpm.
I know VW VR6 owners pay big bucks for a Schrick intake manifold that does the same thing as ours in that the intake path varies in length whereas the stock VR6 engine intake does not.
Just recently I discovered that the vacuum line coming out of the vacuum ball (left of coils) was torn nearly in half so no vacuum to the changeover valve I guess but can't say driving the car made me notice that there was anything odd.
I know VW VR6 owners pay big bucks for a Schrick intake manifold that does the same thing as ours in that the intake path varies in length whereas the stock VR6 engine intake does not.
Just recently I discovered that the vacuum line coming out of the vacuum ball (left of coils) was torn nearly in half so no vacuum to the changeover valve I guess but can't say driving the car made me notice that there was anything odd.
06-10-2003, 03:51 PM
#3
that's a great diagram. Where'd you get it?
<center><img src="http://home.earthlink.net/~ego69/_images/lower_mani_s.jpg"></center><p>here's a pic of the bottom part of the manifold.
Unfortunately I didn't take pictures of the top part as I was only interested in hacking the bottom part to create my own manifold.
Apologize for it's small size as I don't have many pictures at work
Unfortunately I didn't take pictures of the top part as I was only interested in hacking the bottom part to create my own manifold.
Apologize for it's small size as I don't have many pictures at work
06-10-2003, 03:56 PM
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Interesting picture
I was wondering how the intake manifold worked on the inside.
I don't feel the switchover happening either, but I know my vac line is fine. I recently replaced all vac hoses, including the one you mentioned.
Some people here are looking for a way to tweak the point at which the switchover occurs, in order to optimize torque.
I don't feel the switchover happening either, but I know my vac line is fine. I recently replaced all vac hoses, including the one you mentioned.
Some people here are looking for a way to tweak the point at which the switchover occurs, in order to optimize torque.
06-11-2003, 05:34 AM
#5
Actually the action you describe is incorrect. Your description was my assumption too...
As my solenoid was leaking when cold and allowing vacuum to the diaphram when it was cold. However in a correctly working system there is zero vacuum going to the diaphram/switchover linkage at idle. The vac cannister has a spring-assist internally mounted behind the diaphram that keeps the actuator linkage closed and in the low RPM mode. Only when RPM's approach 4,000 should the solenoid open and release vacuum stored in the reservoir to to the diaphram which then will abruptly pull the switchover linkage to the high RPM side.
You can watch that the linkage doesnt move when you start or idle the car due to the internal diaphram spring pushing against the linkage and the solenoid being closed. When you rev the engine to 4,000 RPM's the diaphram will pull it's actuator rod in very quickly... almost "snaps" open.
Very easy to see why this happens so quickly. If you hook a vac tester up to that solenoid you'll see that it immediately releases 17 in Hg vacuum. Only takes 7.5 in Hg to fully actuate the switchover linkage so it's a very quick/abrupt transition when it happens.
Since my solenoid was bad when cold and my switchover linkage moved immediately after starting the car I assumed that all the actions described above were just the opposite of what they are. And had they truly been that way I think a counter-spring would've easily allowed an earlier transition. In fact I'm now working on a "reverse link" arm that will reverse the actions of the actuator to test that theory with a handful of various weight compression springs. Lots easier than adding a switch (when I can no longer put my finger on that electrical gene I misplaced some time ago) with wiring and only difference from stock is the small reversing link and a spring that slips over the diaphram actuator arm that pushes against a small fabricated "L" bracket bolted against one of the diaphram body mounting bolts.
May work, may not as I'm not able to give it more than 10-15 minute attention spans throughout the day due to throttle body demand... sheesh, 9 of them this week alone in spite of 2 cancellations. Is really the "mod du jour" for 2.8 12v owners here in Denver. Severly cuts into my AW time.
You can watch that the linkage doesnt move when you start or idle the car due to the internal diaphram spring pushing against the linkage and the solenoid being closed. When you rev the engine to 4,000 RPM's the diaphram will pull it's actuator rod in very quickly... almost "snaps" open.
Very easy to see why this happens so quickly. If you hook a vac tester up to that solenoid you'll see that it immediately releases 17 in Hg vacuum. Only takes 7.5 in Hg to fully actuate the switchover linkage so it's a very quick/abrupt transition when it happens.
Since my solenoid was bad when cold and my switchover linkage moved immediately after starting the car I assumed that all the actions described above were just the opposite of what they are. And had they truly been that way I think a counter-spring would've easily allowed an earlier transition. In fact I'm now working on a "reverse link" arm that will reverse the actions of the actuator to test that theory with a handful of various weight compression springs. Lots easier than adding a switch (when I can no longer put my finger on that electrical gene I misplaced some time ago) with wiring and only difference from stock is the small reversing link and a spring that slips over the diaphram actuator arm that pushes against a small fabricated "L" bracket bolted against one of the diaphram body mounting bolts.
May work, may not as I'm not able to give it more than 10-15 minute attention spans throughout the day due to throttle body demand... sheesh, 9 of them this week alone in spite of 2 cancellations. Is really the "mod du jour" for 2.8 12v owners here in Denver. Severly cuts into my AW time.
06-11-2003, 10:28 AM
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Re: that's a great diagram. Where'd you get it?
Diagram is off the net from some site I found, can't remember which but it was a French site with an uploaded magazine article about the 'then' new '97 A6/100, the article also talked about the latest technology Audi had used in the development of it's 2.8 V6 engine.
Looking at your intake manifold picture, I've never seen one so clean. Why back when I removed my intake and opened it up it was completely covered in oil and varnish from the valvecase vent pipes. Installed mesh breathers on each valvecover and blocked up the plenum tube holes so no oil goes into the intake anymore.
Looking at your intake manifold picture, I've never seen one so clean. Why back when I removed my intake and opened it up it was completely covered in oil and varnish from the valvecase vent pipes. Installed mesh breathers on each valvecover and blocked up the plenum tube holes so no oil goes into the intake anymore.
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06-11-2003, 11:12 AM
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I've never really trust my repair manual
... that's why I like to double-check. I keep finding more and more fishy claims and stuff that's plain wrong in my manual.
One of these days I'll have to get me one of your throttle bodies. Unfortunatly, I still have the timing belt, brakes, and a few other vital things to do before I can think about the throttle body.
I'm glad they keep you busy!
One of these days I'll have to get me one of your throttle bodies. Unfortunatly, I still have the timing belt, brakes, and a few other vital things to do before I can think about the throttle body.
I'm glad they keep you busy!