Hi guys. New to this forum (mostly lurk around the "other" one), and pretty new to the FD, so please be gentle...



(this is a long post, but if you know about the sequential system, I'd REALLY apreciate your help )



I'm having a boost problem: 13psi dropping to 10psi before transition (which occurs at 5500rpm), then 5psi at transition and only 6psi to redline.



I think I've narrowed the problem down to the precontrol system (I actually have a thread about this at rx7club.com, but it seems to be invisible or something.)



Rather than go into all the details about where I have T'd into and what the results were, I have decided I can't go any further until I really understand how the precontrol system works (I thought I did until yesterday). That's where I need YOUR help .



Here's how I thought the precontrol system worked:



The pre-control actuator has two hoses; one leading to the y-pipe, and one to the air box with a solenoid in between, like this:



Y-pipe(10psig)-----!actuator!-----solenoid------airbox(~0psig)



Since the actuator requires ~10psi to move, I figured it gets this pressure from the y-pipe (there should be at least 10psi there if the primary is working, right?). The solenoid should then be closed for the actuator to move, otherwise the 10psi would just be vented straight to the airbox (which I guess is what happens when the actuator is not supposed to move). This made sense to me. There doesn't seem to be any other way for it to work since it would be difficult to get 10psi to the actuator from the airbox side of the system. HOWEVER, there seems to be a 1-way valve in the actuator on the y-pipe side, like this:



Y-pipe(10psig)-----valve-----!actuator!-----solenoid------airbox(~0psig)



This valve only lets air leave the actuator (to the y-pipe) and doesn't let air into the actuator from the y-pipe. Thus, the actuator cannot get its 10psi from the y-pipe, and my idea of how the system works must be wrong. (I have been testing things, as I said, and I found all this out by putting air through the various hoses.)



So what's the deal? Can someone please explain to me how this system really works? I must be missing something, but I don't know what.



Thank you so much for reading this far and thanks even more for any help.

 

First off, I think you are confusing the precontrol with the charge relief or charge control. The precontrol doesn't go to the airbox. It is fed pressure from a solenoid attached to the front of the UIM. The ecu duty cycles this solenoid, letting only a certain amount of pressure get to the actuator, the actuator also has a pill in the line from the solenoid to limit boost even more. Once the actuator sees 7.5 lbs of boost, it opens up. When it opens, exhaust gases are routed to the secondary turbo to start it spooling. The precontrol is only suppossed to operate from 3,00 to 4,500 rpm.

If you need more help troubleshooting, you can pm me. Make sure to check this thread out: https://www.nopistons.com/forums/index.php?...=ST&f=10&t=8134

--Danny

 

P'cola, thanks alot for helping.



I thought the solenoid was connected to the airbox because I was following the light green line in this picture



http://home.istar.ca/~dvandit/vacuum.jpg



and it goes from the solenoid to the primary compressor's inlet, which is more or less the same pressure as airbox (right?). But I also see now that it goes somewhere else (the UIM I guess, although it doesn't look like the UIM in that diagram). Is it possible to find me a photo showing where it connects to the UIM, or can you just give me a really good description?



Also, one of the tests I did was to T into the precontol solenoid at the hose (under the pressure chamber) that leads to the actuator. At 3rd and WOT the gauge read 2.5psi between 3000 and 5000 rpm. Am I right in thinking that it should have been at least 7.5psi? Once I know exactly where the solenoid connects to the UIM I can check to make sure the line holds pressure (and rule out a leak). What else should I check for? Could the pill you mentioned be clogged or something?





Again, thanks alot for helping (and for being patient with a nooby). I'll try to keep the discussion out in the open rather than pm you, so other noobs can learn too.

 

Have you seen this site? http://www.autosportracetech.com/RX-7/rx7stuff.htm



It's a great place to learn about twin turbo operation and troubleshooting.



As for your problem, what sort of mods do you have? It's very odd to see a transition happening at 5500 rpm, since so much happens at one time. I know you can set this transition point on a power FC, but not on the stock ECU. Also, the 13 psi would indicate that you have some sort of mods. When you say it drops from 13 to 10 before the transition, is that by any chance at 4500 rpm?



Good luck. Sequential turbo problems are a bitch. Mine has worked about 3 times in a row now, which may be a record. Now I'm aiming to screw it up with a buttload of mod.

 

Here's a better diagram of the vacuum hoses:

3 sizes:

huge: http://www.stranglesyphon.com/93vachoses.jpg

medium: http://www.stranglesyphon.com/93vachosesMed.jpg

smaller: http://www.stranglesyphon.com/93vachosesSm.jpg

Thanks to unique TII for hosting them.

 

Yes, I have seen that site. Very useful. I should have listed my mods before - intake, ic, cb. stock ECU. The change from 13 to 10 psi happens very smoothly. It reaches 10psi by ~5500rpm. Nothing happens at 4500 (as far as I can tell). I thought the late transition might be a result of the precontrol valve not opnening. The high primary boost kind of supported that. Hence my delving into the pre-control system. But, maybe I'm "digging in the wrong place" .



Any other ideas - the more the better.

 

Thanks P'cola. I did have that picture too, but not the high-resolution version. Nice.



So, in the pic you just linked to, I am looking at the solid dark blue line that connects to the pink line that connects to the pc solenoid. It doesn't look like that blue line goes to the UIM. More like to the engine. Am I looking at the wrong thing? I really WANT it to go to the UIM, 'cos that would make sense (and it would be easier to get to!), but in the diagrams it just doesn't look like it goes there...what's the deal?

 

I'll have to go look at the car to figure out that diagram better. I can't see where it gets its pressure source from in the picture. The blue lines going to the engine are for the oil injectors. I think you are looking in the wrong place, though. If the car is indeed transitioning late, then it would be a problem with the turbo control actuator and/or solenoids. I'll go into more detail about it tommorrow, when I'm sober.

 

Hope that helps a little.

BTW We are not stuck up, to smart for you dick wads like some people on other forums.

 

Hehe, I wasn't going to say it, but...





Thanks Fd3BOOST, that's a great diagram (I've seen it somewhere else but I don't remember where). That's exactly the way I thought the precontrol system worked. I want to test to make sure the restrictor pill is not the problem. If I take the hose off the turbo (in Fd3BOOST's diagram) and pressurize it, what should I see? Should the actuator move? Only above a certain pressure? I did this and the hose seemed to be closed off - hose held pressure but actuator did not move. Would this be a problem? What does it mean "restrictor pill OR manual valve"? Any info on this particular component would be useful.



P'cola: I guess I'll finish making sure the precontrol is working since I've come this far. Even if it's not the problem, I've learned a hell of a lot. Then I'll look at the other systems.



I really appreciate you guys helping me on thanksgiving, when there's probably food and drink that's far more enticing .