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 https://www.nopistons.com/forums/pub...R )



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 https://www.nopistons.com/forums/pub...#>/biggrin.png .



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" https://www.nopistons.com/forums/pub...#>/biggrin.png .



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. https://www.nopistons.com/forums/pub...IR#>/smile.png

http://nopistons.net/albums/album72/aaw.sized.gif



Hope that helps a little.

BTW We are not stuck up, to smart for you dick wads like some people on other forums. https://www.nopistons.com/forums/pub...#>/biggrin.png

Hehe, I wasn't going to say it, but... https://www.nopistons.com/forums/pub...#>/biggrin.png





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 https://www.nopistons.com/forums/pub...#>/biggrin.png .

The Freshmaker must still be sleeping it off :smirk:



The "restrictor pill or manual valve" means that you could have the stock restriction (pills in 93, and restriction built into the actuator later on), or you could have the Home Depot boost control valves installed. You've probably heard about these, but they're basically just needle valves that you can open and close as needed to adjust boost. It's like having a variable size pill.



If you put pressure in the line that should have the pill in it, the actuator should move. I'm not sure exactly how much pressure it takes, but 10 psi should certainly be enough I would think. The fact that it holds pressure is probably good, since it would likely mean you have no leaks inside the actuator. You asked about the possibility of a plugged pill, and that is possible. The pill is just a short, maybe 3/16" long steel cylinder that has a precision hole drilled in it. If this manages to turn around in the pipe, it could effectively close off the hose. I'd definitely look at both pills (precontrol and wastegate, which aren't the same btw), and keep in mind that you may not have pills if you have a later model actuator for some reason.



FWIW, I don't believe this is going to be your problem. The precontrol is just there to get the 2nd turbo up to speed before 4500 rpm. If it didn't work at all, you'd just see a bigger dip and longer delay for boost when you pass 4500. I'd take a closer look at P'cola's thread that he linked you to, and follow some of those tests. My money is going to be on the charge control system. It sounds like it's not opening properly.



BTW- has anyone gone through the vacuum hoses? Are you very sure they're all OK? More history might help.



Good luck,

Thanks 13brv3. My car is a '93 so I'll check to make sure the pill is ok. As far as I know, no one has touched the hoses. I was planning on doing the hose-job (sometime this winter), but I still want to find out what this problem is first. The car has 20k original miles so I didn't really think I'd need to rush into it. (I bought a car with low miles so I wouldn't have to worry about this stuff https://www.nopistons.com/forums/pub... , but I'm actually quite enjoying getting to know my car so intimately - now that I have some help)



Another reason I think the problem might be the precontrol is that I T'd into the nipple on the secondary side of the y-pipe, just behind the charge releif valve. At WOT in 3rd I saw 0psi up to 5250rpm, then it jumped very suddenly up to 7psi. This makes it look like the secondary is not getting prespooled. Might there be some other reason this happens? I had read on another thread that the pressure here should begin to rise smoothly after 3000rpm (when the precontrol opens). That made sense to me since the secondary should be prespooling and the compressed air vented to the charge relief. Sorry for not putting all this in the original post. I wanted to link to my post at RX7club, which has all the tests I did, but that site is down for some reason. Still, I think that's everything now.



I will check the turbo troubleshooting site for what to look for in the turbo control.



Thanks again.

I also resisted the hose job, and tried to fix my problem without doing it. Silly me :redface: Of course my car had 83k miles, but when I pulled off the UIM, all was revealed. I found one hose completely off, and a couple others that were cracked. This left me with a system that worked most of the time. Eventually, I also found a bad solenoid which has left me with a system that works every time (so far).



If I were you, I'd at least take the time to take a good look without taking the UIM off. If you remove the pressure tank in front of the UIM, and get an inspection mirror, you should be able to see most of the hose connections. I'd say there's about a 50% chance you'll find one off. Take your time, and make it a very careful inspection. You might just get lucky. BTW- there is at least one pipe that you'll see near the front of the rats nest that doesn't have a hose if you have a manual transmission car. There might be two, but I can't remember. You'll also see a few plastic one-way valves that have a tendency to crack. Also look to see that the electrical plugs are connected to all the solenoids. Don't forget to look at the back side of the UIM with your mirror, since there are a few hoses back there as well.



I just have to bet that you'll either find a hose off, or a broken check valve or solenoid nipple. I can't emphasize enough how closely you'll need to inspect all this. I thought I looked carefully, but the hose that was off could easily be seen with everything together. I just didn't look close enough.



Good hunting https://www.nopistons.com/forums/pub...#>/biggrin.png

Thanks again 13brv3. I have taken off the pressure chamber and the precontrol and wastegate solenoids. I see all the hoses in there, and I gave it a quick look but didn't see anything obvious. I'll take your advice and be much more systematic.



Correction to earlier post: On one of my posts above I said I presurized the hose going from the y-pipe to the precontrol actuator, and I said the actuator did not move. Well, I did the test again just now and it DID move. I must have screwed something up the first time. I am now satisfied that I understand how the precontrol works, and I am 95% sure it is working fine. I'll tap into an actuator hose the next time I go for a drive and verify it gets pressure, but right now there is alot of stuff off the car, so I'll do a thorough inspection of the hoses and check the turbo control system before I put it back together.



Thanks alot for the help you guys. I'm sure I'll have more questions before the end of the weekend...

Well, I had a better look at the rats nest. Didn't see any cracked or popped-of hoses, but there's still alot I can't see...



I tested the check valves going to the vacuum and pressure chambers. They are ok. And there are no leeks in the pressure chamber or its hoses. Don't know about the vacuum side since I guess some of the solenoids are open, and I haven't isolated them all yet to close them off.



I'm still not 100% sure it's not the precontrol. Remember the test I mentioned earlier that I got 2.5psi on? How would that happen if the precontrol were working? Should be much higher, right? The only place for there to still be a problem with precontrol is in the signal that the solenoid receives (everything else has been tested). Maybe the connectors for the precontrol and wastegate are switched. I know I should look for the matching dots, but there is only a dot on the wastegate solenoid, not any of the connectors. The connector that is currently on the precontrol solenoid has a pinkish bit on the plastic protecting the wires. Could this tell me anything?



Even if it were the turbo control, would that explain the late transition? I still don't know what exactly causes all the solenoids to click over at 4500rpm. Does the ecu send the signal based on the rpms? Does the ecu see the same rmp signal as my tach? Might something be wrong with the ecu or the rpm signal it receives? Or is there a simpler explanation. (None of the troubleshooting lists I have read so far deal with late transition.)



Any ideas on any of this?

It's my understanding that the ECU controls when the transition happens. I'm pretty sure you can set a different RPM with aftermarket ECUs like the Power FC. Is there any chance the original owner sent the ECU off to be modified? There are a number of companies that will modify the original ECU for bolt-on mods, but I'm not aware of any of them changing the transition point.



While on the subject of ECUs, has your car had the ECU recall? It corrected some electrical problems that caused the engine to stall sometimes when the car was under high electrical load. If you're on the list to get the upgrade, it's free, and would let you test the ECU. You'd have to give your VIN to the local Mazda dealer to let them look it up.



I had wondered about the possibility of an RPM miscommunication between the tach and ECU, but I doubt it's at all likely. Nothing is impossible though.



Back to the problem- I'd start looking now at the charge control valve when you get things back together. You may need to T into the control lines for that, to see what it's doing. That valve should be opening at 4500 RPM, and the result should be obvious on the boost gauge. I think you're going to have to just start checking every vacuum signal you can while testing the car. Keep a good written record, and see if that turns up anything. Sorry I can't be any more specific.



Cheers,

pull off your uim and look for some leaks and blown off hoses



STEPHEN

13brv3: Thanks again. I've called the 800 number to find out about all the recalls, and there wasn't an ECU one. I don't think the ECU was modified. Would I be able to tell if it was?



I'll start looking at the charge control valve.

You would think there would be a sticker or at least some writing on the outside of the ECU if it had been modified. It's probably stock as you expect.



BTW, did they say you weren't on the list for an ECU, or your car already got it? I just found the recall letter- SSP39, and the VIN range was from P0200062 to P0209530. You must have a late 93 car if you missed this range.



Cheers,

My VIN is within that range. They said the car had required 2 recalls and both had been done. The brakes and the fuel line I think. Definitely not ecu. Maybe I'll call back and check. Thanks for the info.

Sorry guys I haven't been paying attention here.

This link may come in usefull as well if you haven't already checked it.



**** load of info on stock twins and their related problems and how to's

Have you checked to see that the precontrol rod is attached to the door, via a little c-clip?

There's a thread on the other forum that suggested that the ECU turns down the boost at around 6k RPM. The theory states that some stock ECUs are programmed to do this, and some are not. Supposedly, if you have a normal 10-8-10 pattern, you will either get 10 all the way to redline, drop slowly as RPMs build (plugged cats or intake), or drop instantly at some point (ECU programming).



Why am I telling you this, you ask? Well, I just drove my car to see when and how my boost fell from 10 to 8. In my car, the drop is immediate, and happens at 5500 RPM. I'm starting to wonder if you have no transition, and the 5500 RPM drop is due to the ECU programming.



This is way out there as far as theories go, but something to consider maybe.



Cheers,

Checked out ok. Thanks.

There's a thread on the other forum that suggested that the ECU turns down the boost at around 6k RPM. The theory states that some stock ECUs are programmed to do this, and some are not. Supposedly, if you have a normal 10-8-10 pattern, you will either get 10 all the way to redline, drop slowly as RPMs build (plugged cats or intake), or drop instantly at some point (ECU programming).



Why am I telling you this, you ask? Well, I just drove my car to see when and how my boost fell from 10 to 8. In my car, the drop is immediate, and happens at 5500 RPM. I'm starting to wonder if you have no transition, and the 5500 RPM drop is due to the ECU programming.



This is way out there as far as theories go, but something to consider maybe.



Cheers,[/quote]

Interesting idea. Does make sense. I'll have to do some reading on it.

Well, I had the car back together and everything set up to double check my 2.5psi result (the only thing that still points to precontrol). I was also going to switch the wiring on the precontrol and wastegate solenoids, just to see what happens. The car was warming up in the the garage and then...snow. Can you believe it? Maybe I need a break anyway.

Snow didn't last so I got to run my tests. I T'd into the hose that connects the precontrol solenoid to the precontrol actuator (on the solenoid side) and also to the short hose that connects the actuator to the y-pipe. The first test was a repeat of the one I talked about before where I got 2.5psi. I got the same this time. The second test was different. I got over 10psi at around 4000rpm (easily enough to open the precontrol valve). This test is about as close to the actuator as you can get. Conclusion: the precontrol IS working.



I had thought that both of these tests should give me the same pressure (since they are in the same line), but I guess the pressure drop between the actuator and the solenoid is quite large (about 7.5psi). This is an important lesson since it applies to tests in any system. Don't assume that pressures are the same at different points in the same line.



And the lesson for anyone debugging their precontrol is - T into the hose going from the actuator to the y-pipe, not to the solenoid. The y-pipe hose is a little harder to get to, but that's the best way to do it.



Since the problem definitely not the precontrol, I think I should start another thread with a more appropriate title.



Thanks for everyone's help on this.

For the benefit of future newbie searchers...



I am an idiot; I should have gone straight here:



http://www.rx7turboturbo.com/robrobinette/.../boost_note.htm



This has everything I needed to know about precontrol and boost control in general.