weird boost problem

[Vitwagen]

Thanks for the replys Guys.

I was surprised to find when I got my early AAZ, it had neither EGR, nor BOV on the inlet manifold, so it's not the BOV! (My 1.6 did have it, so I know what I was looking for).

The thought of the MBC being backwards had occurred to me too. I checked, and it has the ball pointing towards the turbine, spring towards the actuator.

And the actuator already applies a little pressure to the wastegate proir to opening. I wound it in a few more turns, but it wasn't any different.

I'm proper stumped. 

[R.O.R-2.0]

This may be a stupid question, but I have a universal wastegate i use with my vnt, how much exhaust leakage will cause a drop in boost?  I imagine that will all depend on turbine/ hot side size, back pressure, revs, etc.

I have a similar problem the wastegate spring is for 7 psi and I think the exhaust pressure is pushing it open as I can only get about 8 psi without any boost control hooked up.  I'm going to add a spring and see if that helps.

sorry, vanes work differently..

they are not a wastegate, so they cant be pushed open..

you only make 8psi because your wastegate is set to 8psi, and its opening the vanes, and the turbo quits boosting..

[rodpaslow]

Yes, port in intake is blocked off(giles block with o-ring) - the wastegate is over the port that was for the egr valve and by pass runs to just past the outlet out of the vnt.

[rodpaslow]

I don't have any vane control hooked up except a spring holding the vnt vanes closed.  Nothing hooked up to the wastegate to open it.  I'm assuming then, that the back pressure/drive pressure is more than 7 psi and it's opening the wastegate.  Is this logical / true?

[R.O.R-2.0]

I don't have any vane control hooked up except a spring holding the vnt vanes closed.  Nothing hooked up to the wastegate to open it.  I'm assuming then, that the back pressure/drive pressure is more than 7 psi and it's opening the wastegate.  Is this logical / true?

none of what you said seems very logical to me..

VANES are NOT a wastegate.. a VNT doesnt/shouldnt have a wastegate. maybe a wastegate actuator working the vanes, but not an actual wastegate..

they (vanes and a wastegate) dont even function anywheres close to the same..

the drive pressure is NOT opening your vanes.. nothing is.

if you got a spring holding them closed, then they are closed 100% of the time..

i can have the actuator come disconnected from my vanes, and they will sit wherever they come disconnected.. they wont open up, or close down, or anything like that. they just quit moving.

its really DUMB to run a VNT with no form of vane control... i know this from personal experience!

[rodpaslow]

I realize you don't need a wastegate with a vnt.  I have it to control the overshoot, it's a vnt 17.  I've got a great running motor after all the work I've done and I don't want an overshoot to kill what I have at the moment, so I have a wastegate so there's no chance of it going over what i have the wastegate set to.  Sorry for the mis-information.

However, I still have the problem, of only 8 psi max(I think 8 lb spring), with no control to the wastegate, vnt vanes closed (I willl add a control when I figure out why I'm not getting to 18-20 psi).  Intake blow-off is plugged, I checked all the boost tubing and it's all good.  It has to be on the exhaust side of things.

I guess I'm asking if the drive pressure would open the 8 lb spring in the wastgate?  I've always assumed-thought the wastegate will not open until there is a boost pressure moving the diaphram to open the valve.

[R.O.R-2.0]

the VANES create LOTS of back pressure.. more than the boost..

so, yea, your wastegate is probably being blown open from the drive pressure..

why not make your vanes function like they are supposed to? if you have your turbo closed down all the time, with a wastegate to control boost, then all you are doing, is making the turbo SUPER RESTRICTIVE, and using a wastegate to do the job of the vanes.. sure, you got 8psi boost, but you prolly got 15psi drive pressure because your vanes are closed down.

why are you trying to wastegate a turbo that can not operate correctly with a wastegate?

take the wastegate off..

hook up the vanes..

thats the only way it will ever work right.

you are not making 20psi, because you have a wastegate. take the wastegate off, and use the vanes to control max boost!

the way you have it rigged up, will never really work RIGHT..

vanes closed = HIGH drive pressure.

high drive pressure = blown open wastegate..

an 8psi spring in a wastegate doesnt take much drive pressure to be blown open.

if your turbo cant produce sufficient drive pressure, then it cant produce boost either!

[rodpaslow]

ROR your right on the money.  I want to have a proper control and have it ready to put in place.  I just don't want to have 30 psi an not notice it and ka-boom with a fibre head gasket.  When i have the proper control in place (very shortly) it will work like it should -much thanks for responding! I'm not even really looking for 20 psi anyway - I'd be happy with 15, and the vnt is starting to produce boost at 1800 rpm -perfect for the way I drive and where i drive.

[vanbcguy]

Thanks for the replys Guys.

I was surprised to find when I got my early AAZ, it had neither EGR, nor BOV on the inlet manifold, so it's not the BOV! (My 1.6 did have it, so I know what I was looking for).

The thought of the MBC being backwards had occurred to me too. I checked, and it has the ball pointing towards the turbine, spring towards the actuator.

And the actuator already applies a little pressure to the wastegate proir to opening. I wound it in a few more turns, but it wasn't any different.

I'm proper stumped. 

Missed that it was an AAZ... Yep, no BOV there.

Well, if you want to rule out the MBC you can leave the wategate completely disconnected, just watch your boost gauge and adjust with your right foot accordingly.  If you still have the same symptoms then you're looking at a bad spring in the wastegate actuator or some other problem.  If they go away and you suddenly get consistent high boost then there's something wrong with the MBC.

[rodpaslow]

Actually this is on a 1.6, but I've since added the vane controller and the wastegate problems have dissappeared.  I guess I should have mentioned my problem was with a VNT (I have a wastegate added to it) and with just the vanes closed, it was opening the wastegate because of drive pressure.  Now I have a control hooked up, which reduces drive pressure the waste gate really doesn't do anything unless I floor it fast, boost shoots up and wastegate controls it to about 15 psi, is what I have it set to with a MBC - this is just until I can fine tune the control to hold it to boost that I want.

Its much more driveable and easier on everything - oil temps dropped, engine temp , egts, etc - I think simply due to better turbine flow and less drive pressure....problem solved for me.

[Vitwagen]

Missed that it was an AAZ... Yep, no BOV there.

Well, if you want to rule out the MBC you can leave the wategate completely disconnected, just watch your boost gauge and adjust with your right foot accordingly.  If you still have the same symptoms then you're looking at a bad spring in the wastegate actuator or some other problem.  If they go away and you suddenly get consistent high boost then there's something wrong with the MBC.

That hadn't occurred to me! Will try asap. Thanks!

[gldgti]

it was opening the wastegate because of drive pressure. 

thats what I said