I've been tracking down the source of my problem for weeks now. I've got a single turbo, t04s. I'm loosing boost at the top end for some reason. I've tested for boost leaks and I found many, I fixed them all and then did a 3rd gear pull, still loosing boost. So I bypassed the Profec B boost controller and ran a straight line from the compressor to the wastegate. This still did not solve the issue.

I'm rattling my brain trying to figure out what causes a drop off in boost like this. The rate at which the boost falls and the rpm at which it falls including the amount that it falls is identically the same at 10psi with the boost controller on and off (spring is 9 psi but when the controller is connected but off it runs 10psi), 15 psi with the boost controller on, and 9psi on spring with the boost controller bypassed. I always loose .15 ish bar of boost. From 15psi to 13, from 10 to 9.

All I can say is,

...help

 

Clogged cat?

 

busted wastegate?

 

No cat.

Never thought of that. How common is that?

 

Diaphragms can fail, the valve seat "ring" gasket can leak. It happens often enough that it's worth looking into. I've seen ebay wastegates stuck open out-of-the-box.

 

Thanks for the idea. What do you propose is the best way to test the wastegate for leaks?

 

How is your boost controller and wastegate hooked up?

thewird

 

What exactly do you mean? I just recently learned how a boost controller actually controls boost. Never really cared until now lol.

This is my setup as far as I know it. Boost controller display is in the center dash. Boost control box is next to the abs unit on the fender. A vac line comes from the intake system just after the compressor and runs into the "in" nipple of the control box. A line comes out of the "out" nipple of the control box and runs down to the wastegate. When I bypassed the control box all I did was get a double male vac connector and make it so the line coming from after the compressor goes directly to the wastegate and never touches the control box.

 

So you only have one line to your wastegate?

thewird

 

Yes, is that bad?

 

Well pull the gate off and make sure whatever seal/gasket whatever doesn't look damaged. Here is a general writeup about diassembling a wastegate: http://www.autosoftsys.com/supra/wgfix/ . I'm not saying you should just jump into that head first, but it's something to keep in mind if it becomes more and more likely that the wastegate itself is leaking.

As for having one line to your wastegate, well that's not necessarily "bad." You are controlling it like an internal wastegate by using the side port only. It's not commonly done on Rx-7 applications but you will see a lot of Subaru guys do it. I prefer to use both the top and side port. If your wastegate is being pushed open due to exhaust backpressure then hooking it up using the top port and side port will help with that.

read this article about the different solenoid and plumbing configurations. External gates are closer to the bottom. http://www.perrinperformance.com/pages/show/113

 

great link (Perrin)re boost control++++++++

arghx, thanks for all your high value posts.

howard

 

Yah, thanks arghx for that link. I knew how it worked but didn't know how it mechanically worked on the inside ^_^

And you basically explained what I was going to get at about the boost controller hookups

thewird

 

It's so simple isn't it? After I read that article, which is by far the best discussion of boost control on the internet, I knew I could use a factory FD boost control solenoid on an external wastegate. I just took the two port wastegate solenoid and plugged it into the factory harness, then used the solenoid to feed air directly to the top port of the gate. All I needed was a small bleeder in-line to relieve pressure. then i adjusted the duty cycles in the PFC and now I'm getting pretty consistent boost around 16.5-17psi.

 

Man that really was a good article. i have an internal wastegate and just routed all the vacuum lines for my setup yesterday. Pretty interesting how all that works. Nice post sir.

 

Ok that article was great. What would be the most likely failure in my case? If the diaphragm was torn then I would over boost since I only have one line going to the wastegate from the compressor.

How is it possible that I can pull and hold full boost at 4-5k rpm but then drop off later regardless of how much boost I set it to. Would tightening the wastegate screw do anything useful? Maybe a heavier spring? I don't know the spring rate that is in there now since I know the screw has been tightened already. I guess I could unscrew it to the minimum and do a run to see how stiff the spring is.

Also is it normal for it to run 9 psi on spring when bypassing the controller but to also run 10psi on the same spring setting with the controller connected but turned off? I always assumed turning the controller off would just run on pure spring but it seems to be different.

 

connect the controller to the top port of the wastegate before you try anything else. What EBC are you using?

 

Greddy Profec B possibly a spec 2. By top port you mean the port closest to the manifold? Not the one near the pre-tension screw.

 

The one furthest away from the manifold. Keep in mind you still need a full boost source for the bottom part of the wastegate. Basically like this... Refer to your Greddy manual for which ports on the solenoid to use for external wastegate type.



thewird

 

Wait, I need a straight line from the compressor to the wastegate that bypasses the controller and then I put a T in that line and run one to the controller and another one out of the controller? I'm confused because I only see 2 ports on the controller. I thought the air goes from the compressor to the control box and then out to the wastegate.

Are there different styles of controller? Like mine with one in and one out. And other controllers have one in and one out plus an atmospheric dump?

I think mine is hooked up like a manual controller. Unless I can't see the atmospheric dump...

EDIT: Profec B Spec (not Spec II)

 

Ok this is the installation manual for my Profec B Spec (the controller with no LCD display).
http://www.greddy.com/img/PHP/products/pdf/687.pdf

If I'm reading this right for an external wastegate, then the previous owner has the system set up wrong. I have NO direct line from a boost source to the wastegate. The only line running into the wastegate first passes through the boost controller box and enters the port nearest the manifold. I'll try to get some photos tonight If I can find my camera.

 

Just hook it up like the diagram but source it off the turbo instead. I'm not sure if the older style controllers need it off the intake though.

thewird

 

Well my concern is that the diagram shows one line going from compressor to wastegate. Then it shows another completely separate line going from compressor(or any boost source) to the box then from the box to the top of the wastegate. All I have right now is the line with the box in the middle but it goes to the port closest to the manifold instead of the top port. I do not have the pure boost to wastegate line anywhere.

Also a buddy of mine said that the boost controller works better when the source is the manifold rather than just after the compressor. Any truth to this?

 

your boost controller is hooked up like an internal wastegate right now. and the old profec B uses a stepper motor, not a 3 port solenoid. take the line that comes from the motor and goes to the side port, and hook it to the top port. make sure the controller is set to external wastegate.

then run another line to the side port, or tee it off. take a look at this:



by "top port" i am referring to the pressure source for the Profec stepper motor. Your choice of pressure sources will affect how much max boost can be achieved and also affect the likelihood of boost spikes.

 

Thank you guys very much for the help. The problem is fixed. Turns out the boost controller was set to "actuator when overboosting occurs" I rerouted the lines as the manual said to. Line from compressor to control box then to top of wastegate. Then ran a separate line that I T'ed from the BOV line(which originated from the intake manifold) to the side port of the wastegate. I set the boost controller to regular "external" and it now holds boost. Looking to finally break 400rwhp. Wish me luck.