OK... So i know that the air pump is suppose to control the actuators that work the VDI so removing it is usually a bad idea due to a loss of power.. so how come if i take off the belt to the air pump i fell no power loss. if anything it actually felt a little faster. obviously something is not quite working right. so the question is what do i need to check to find where my problem is.. Im not familiar with how the whole VDI thing works so any help would be great..

 

It's quite possible your 5/6th ports are stuck closed and thats why you are not noticing anything. You need to make sure they are moving freely, when you are checking them, they should be really easy to move with no resistance. If you feel resistance then it is probably dirty with old oil and the lower intake manifold needs to be removed to remove and clean the sleeves. It is also possible your vacuum lines are not hooked up to it correctly.

The VDI is located on the upper intake manifold, on the drivers side where the middle and top manifold meet. You will see an actuator on there, two bolts hold it down and you can pull it out. Make sure the "lever" behind the actuator moves up and down.

5/6th ports are located above the exhaust manifold. They have the same type of actuators the VDI had, just look for two. Two bolts removes them, make sure they move freely up and down (the levers that are connected to your 5/6th port sleeves, same concept as checking the vdi).

 

I did notice that the 5th and 6th port actuators do move when i rev the engine.. but as far as the vdi i think i found it... please correct me if im wrong here... the UIM is made up of roughly 3 different pieces.. throttle body portion, the upper piece that connects to that.. and then the piece under that that has the same design as an fd manifold.. on the under side of last said piece there is a cylander shaped thing with a lever attached to an actuator type do-hicky. which i found was missing a C-clip and the bar coming out of the actuator was not connected.. so i connected said bar and.......................nothing.. still not working. did not notice any change and i could not see it move any at all. i can move it with my fingers and it is tough to move but not like its stuck. it feels more like a spring makeing it move back. i can suck on the hose connected to it ( any comments on that and ill hunt you down ) and it will move no problem. I also found a mystery hose that appears to be coming out of the lower intake manifold. its in the very back on passenger side. it may have something to do with the air pump but im not sure. it has vacuum on it when i rev the engine and it appears to have no affect on the idol when i block it off.

 

Someone was trying to explain to me how the VDI works. If you don't have sufficient back pressure in your exhaust, it doesn't work properly. I'm not talking about the port actuators. I know the difference between S4 (No VDI, actuated by exhaust pressure) and S5 (VDI, actuated by air pump). But it seems like that the S5 N/A runs best if left alone.

 

The VDI works by changing the runner length (shorter), which shifts the power band up in the RPM range. Exhaust back pressure doesn't really have anything to do with it. If anything, you need a free flowing exhaust at higher RPMs.

The pressure wave that causes the supercharging effect comes about when the intake ports close. But that's not really a VDI thing; it's just a natural rotary effect that the VDI takes advantage of when the runner length shifts.

 

i actually have the same problem but with no mystery hose unatached. all the little actuators move freely and the hose is hooked up to the exhaust.its all stock and its an s5. would it be a bad idea to take the 5th 6th port actuators out and just run them open all the time? and my air pump is missing is there a way i can hook up a tube from the stock air box to the tube that is suposed to got from the air pump to the engine?

 

Just put an air pump back on and be done with it. Wiring open the ports kills bottom-end, and no you can't connect the hose to the air box. It wouldn't do anything. The air pump creates pressurized air. About ~2.1 psi is needed to activate the aux. port actuators, and something similar for the VDI.

 

Yah i know what you mean about leaving it alone.. unfortunately when i got the car someone had already messed with it... im trying to get it to run like it should. i getting beat by stock s4's right now and i dont like it. hehe

 

as far as the 5th and 6th ports go does it matter if i have an aftermarket header since they are run off of exhaust pressure

 

Do you have an S4? If you have an S5, exhaust pressure has nothing to do with it.

 

She's an S5

 

Yeah, then having headers isn't going to make any bit of difference. You need the air pump to open those ports.

 

woult it work if you hooked up the exhaust tube to the front where the air pump goes. some one just told me that it would because the exhaust even stock creates enough presure to open them. i dont know if this is true can some one help, kinda sounds dumb to me but kinda makes sense at the same time.