I started asking about this in another thread where I thought the problem was the precontrol, but I think I've ruled that out now.



Here's what I get at WOT in 3rd



0-5500 rpm: boost steadily decreasing from 13psi to 10psi

5500 rpm: 5 psi

5500 rpm-redline: 6psi



With the high initial boost, I'm thinking that the wastegate or charge relief might be the problem. The low secondary could be just a leak somewhere, but the late transition is very confusing. Anyone experience a similar problem? Any suggestions would be much appreciated. Thanks.



(my mods: intake, smic, cb)

I'd check the CRV. How bout boost leaks? Hear any whooshing? Stock Y-pipe and couplers?

I don't hear any leaks (but that doesn't mean there aren't any). The y-pipe and coupler is stock. The efini is on order. I had a pretty good look at the y-pipe coupler when I was debugging the precontrol, and it seemed ok; no huge holes like some people report.



Why do you say to check the CRV? Because of the high primary or because of the low secondary?

The low secondary. I have never had a problem with this, but some people say that it will cause low secondary boost if not functioning properly.



You can always swap the BOV and CRV to see if that fixes the problem... Then you'll know if the CRV is bad. Both valves are the same, just used differently. (Can someone verify this?)

Here's a hypothesis. Can anyone agree with this or explain why I might be full of sht...



The primary boost decreases before transition because the precontrol is gradually bleeding off more exhaust to the secondary (as it should). But the wastegate, which should (I guess) opposite from the precontrol to keep the boost constant over this region, is not working. i.e., the wastegate should gradually close and the precontrol should gradually open, thereby keeping the primary boost pretty constant, exept that maybe my wastegate is not working so my boost starts out too high and decreases.



This is just a theory, but if there's some reason it couldn't be true I'd like to know so I don't waste time checking it out.



And it still doesn't explain the late transition. That's the most confusing part of this whole problem.

MAybe some things are just sticky? Is there a way to spray carb leaner thru the system without having to take it completely apart?

I am always cautious about spraying anything. Does carb cleaner harm plastics or rubber?

That I don't know. I don't think so however. I was hoping someone else would chime in and throw up an idea or 2..

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

I just read on the FAQs at



http://www.autosportracetech.com/RX-7/rx7stuff.htm



that my boost gauge might read several psi (3-4psi by my calculations) higher because I live at 7000ft above see level. However, I'm not sure if I completely understand this since the gauge reads very close to 0psi when the car is off. Maybe the gauge automatically complensates.



Anyone have any experience with boost at high altitude?



Does the ecu (and mine is stock) regulate the pressure to be 10psi above sea level or 10psi above the measured atmospheric pressure?

Hi again,



I still think the lack of a transition at 4500 is a big clue, that should be investigated. Have you T-ed into the charge control actuator on the y-pipe? That will tell you when the charge control actuator is being told to open. If you see transition on the vacuum port, but don't see it on the boost gauge, then maybe the actuator is sticking closed. If the vacuum signal doesn't change until 5500, then we'll have to look deeper into why. While I was T-ing into the charge control actuator, I'd also put the vacuum tester on it and make sure you see it actuate.



Another thing that would be interesting (and you may have done this already), is to T into that nipple that's on the secondary side of the y-pipe. It would be interesting to see what the gauge sees at that point. This will give you some additional info on whether the secondary turbo is pre-spooling, and whether the charge control is opening.



Ain't sequential fun https://www.nopistons.com/forums/pub...#>/biggrin.png



Cheers,

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





This test I have done. It read 0psi up to 5200rpm (or at least, until slightly before 5500rpm), then it jumped very quickly to 7psi. Apparently (according to this thread: http://www.rx7club.com/forum/showthread.ph...rbo+precontrol) I should be seeing a smoother build up of pressure, corresponding to the precontrol opnening. This is one of the tests that pointed me to the precontrol in the first place. This makes it look like the charge control is opening, but just late.



It also makes me think that there is still one piece of the precontrol puzzle that I did not check. I did not check that the valve is opening, even though I know that the actuator is moving and it is connected to "something" with a c-clip. If the valve really is opening, I should see something at this nipple before 5000rpm, right? Have you done this to test on a working car before? If the precontrol valve itself is stuck or broken, how can I tell?



As for the charge control actuator, I have not tested it yet. When I get off work I will T into it, as you suggested, and see when it gets its vacuum?. And I'll also verify that the actuator moves under vacuum.



Thanks again 13brv



I thought debugging computer code was fun - the sequential turbo system makes fortran look easy https://www.nopistons.com/forums/pub...#>/biggrin.png

I'm with Rusty on this one. Start T-ing into vacuum lines of things which occur around transition. Like the CRV, the CCV, the TCA, the vacuum tank, and the pressure tank. If you have a leak in the vacuum chamber, that could cause a late transition, due to the pressure side of the TCA having to do all of the work. Your theory on the wastegate not working doesn't make much sense to me, because until the transition, the precontrol is doing the boost control, not really the wastegate.

Ok, I'll hold off on messing with the wastegate then. I'll do as you guys advise.



What is the simplest way to check the vacuum tank (the pressure tank is easier to check since it isn't connected to as many solenoids)?



Thanks.

Just "T" into any of the lines that use the vacuum chamber. I "T"ed into the one coming directly off of it, but you can go in anywhere before the solenoids.

Ok, the first thing I checked last night was the charge control actuator. The shop manual says it should move with 1.9inHg applied. I had to apply 5inHg to get it to move all the way, so maybe it's a little sticky. I need to T into that line while driving and see what the pressure is; maybe this difference is insignificant.



Next thing I checked was the charge relief valve - works perfectly, tested it exactly as the shop manual said. I even tested it again using the hose it connects to in the rats nest to rule out a leak between there and the valve.



I also checked the charge relief solenoid. It works fine.



I didn't check the charge control solenoid yet since it requires removing the UIM and so far I have managed to avoid this. Still, I am running out of things to check so it might be time to go deeper. I may wait until my y-pipe and dp arrive.



I need to verify that both the CRV and CCA are working when the car is running, but this morning there was 6" of snow on the ground, so that'll have to wait.



I haven't checked the vacuum chamber yet. I T into any vacuum line, and then what? should it hold vacuum? I tried this, but some of the solenoids must be open. Should I try again with the car running (or just turned on?)? what should I see?



Thanks.

"I need to verify that both the CRV and CCA are working when the car is running, but this morning there was 6" of snow on the ground, so that'll have to wait."



Ack, snow.... I need to drive my car to let the PFC "learn" not to hunt for my idle speed, but it's barely 60 degrees out, brrrr :smirk:



Operational tests of your CRV and CCA will be interesting. I'll look forward to hearing about the results next Spring :stickpoke:





"I haven't checked the vacuum chamber yet. I T into any vacuum line, and then what? should it hold vacuum? I tried this, but some of the solenoids must be open. Should I try again with the car running (or just turned on?)? what should I see?"



The vacuum chamber is just to the drivers side of the alternator, and it only has one hose going to it. To test the chamber, just pull some vacuum on that hose to the chamber, and see if it holds. You just want to make sure the chamber isn't cracked. When you're under boost, that chamber is the only source of vacuum to anything that needs it.



Cheers,

Sounds simple. I guess I just try to make things too complicated :redface: .



I just had another thought (scary, I know). Remember I mentioned I did the test on the nipple on the secondary side of the y-pipe and got 0 to 5200psi and jumped to 7psi after? Well, here's my thought: What if the charge control was working, or at least, was opnening at 5200, but what if the secondary turbo was not spinning? Wouldn't this give me that kind of result? i.e., the pressure I'm seeing is the primary charge air flowing backwards through the charge control valve! This would mean, though, that the secondary turbo did not spin under precontrol either. This would be a serious problem.



Any thoughts on how far up the BS-o-meter this theory ranks?

Maybe not as far as you'd like it to be https://www.nopistons.com/forums/pub...O_DIR#>/11.gif



Rusty

I don't think that the CCV will open unless there is boost on the back side of it. I could be wrong, but I "think" that for it to open, there has to be equal boost pressure on both of its nipples. And I "think" that its other nipple gets boost from the secondary turbo. I would recommend not checking your vacuum chamber with a pump, but rather checking the entire system by "T"ing into the line Rusty is talking about, starting the car for long enough to build a vacuum, and then turning the car off. If you lose much vacuum at all, no matter how long the car has been sitting, then you have a leak. That leak could be your problem.

That was a good point, and a much better test. A couple times, I've pulled off vacuum lines a couple days after the last time I drove the car, and there was still vacuum.



Rusty

That sounds right about the secondary boost needed for the CCV to open (phew).



I like that vacuum test. Not only does it test the entire system but it is also very easy to do https://www.nopistons.com/forums/pub...#>/biggrin.png (and I can do it in my garage).



Thanks P'cola FD and 13brv





by the way, I have a thread going on rx7club about how the boost gauge (and the boost itself) is affected by altitude. This may partially explain some of my strange boost pattern, but I haven't entirely figured it out yet. The thread is here:



http://www.rx7club.com/forum/showthread.ph...threadid=137455

I found some info that refers to transition at 5500rpm!



At the boost control section of Rob Robinette's site:



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



It says that the manual suggests transition occurs at 5500rpm under lite load. Maybe my problem is that the ECU thinks load is light. Does anyone know where in the manual it says this; I'd really like to read it first-hand.



How does the ECU know that load is light? Does it compare throttle position and rpm?

I think that if your ecu thought the engine was under light load, then it would be running on the fuel maps for light load. And if it were running on the wrong maps, you would be worried about a lot more than just boost problems right now.

I'm really starting to think you are having a TCA problem. Check the vacuum chamber's storage, the operation of the TCA, and "T" into the lines going to the TCA when it stops snowing. I think your problem may lie therein.

Agreed. It's just that the whole 5500 thing is really bugging me.







I will do what I can tonight in the garage, and I'll do the running tests as soon as the weather will allow.



Man, it's really good to have people to bounce ideas off of; keeps me from wasting hours (days?) chasing my ass.

The vacuum system is fine. I hooked a vacuum pump to the hose on the front side of the check valve and the system held 15inHg steady for over 5 minutes. I also checked the check valve.



I checked the TCA by hooking a pump to it's hose in the rats nest. It worked fine (watched it move from under the car when the pressure was released). I think the only actuator I have not yet checked is the wastegate.



It may be a while before I can do any running tests due to the weather. I'll revive this thread and describe the results when I get them.



Thanks everyone.

Keep us posted. I'm interested to see what you come up with!

Ok, today was my day off, and the roads were dry https://www.nopistons.com/forums/pub...#>/biggrin.png .



T'd into TCA (at the hose in the rats nest). Here's what I get:



<3500rpm: 15"Hg

between 3500 and 5200rpm: 0psi

>5200rpm: 7psi



I'm not sure about the change at 3500rpm. Can anyone shed any light? (Does one solenoid click at 3500 and the other at 5200?) Is it supposed to do that? 7psi should be enough to open the TCA (which I checked the other day - see post above), so the secondary turbo should be seeing exhaust (albeit a little late at 5200rpm!).



I then T'd into the CCA (also at the rats nest, just off the solenoid). Here's what I got:



<5000rpm: 0psi

>5000rpm: 6.5psi



This should also be enough to open the CCA: Thus, I should be getting compressed air from the secondary. Note that the 5000rpm in this test was distinctly different from the 5200 of the TCA test, implying that the CCA opens slightly before the TCA. I guess this is normal? Either way it doesn't seem like a problem.



These results seem to point to the CRV as the reason for my low secondary boost; maybe it's staying open or something. I'll T into that next (when the car is cool).



Still no clue as to the late transition. Any ideas?



By the way, I also hooked the boost gauge back up to the UIM and when for a final run, just to make sure my boost pattern was the same: it was the same (13psi, dropping to 10 by transition at 5500rpm, 5psi at transition, and 6psi to redline)



What do you guys think?

Oops!!!! https://www.nopistons.com/forums/pub...>/blackeye.gif



I'm really sorry, but I had a brain fart on that previous post. Everywhere that I say CCA I should have said CRV.



So, the two tests I just did was the turbo control actuator (TCA) and the charge relief valve (CRV).



Now, if I'm not mistaken (and I probably am) doesn't the CRV need a vacuum to open? It's only getting 0psi when it needs to open (before transition, right?). I need to double check. I have all the info, I just need to look at it. Maybe this is my problem (or one of them at least).



Sorry I'm making such a mess here. In a hurry to do as much as I can before it gets dark.

Which TCA solenoid line did you "T" into? There are two. One attached to the ACV for vacuum, and one in the rack for pressure. They should both switch over at 4,500 rpm. If they aren't, then I'd try checking the solenoid's vacuum/pressure source. If that looks good, then it may be related to your ecu or wiring. This is pretty wierd.

Well, slap me like a bad dawg, I did it again :redface: : I mixed up the results of the TCA and CRV tests. What the results of the TCA and CRV tests should have said was



CRV:

<3500rpm: 15"Hg (valve is open)

between 3500 and 5200rpm: 0psi (valve is closed)

>5200rpm: 7psi (valve is still closed)



(I just now double-checked this result by T-ing into the vaccum hose right at the CRV)



TCA

<5000rpm: 0psi (valve is closed)

>5000rpm: 6.5psi (valve is open maybe - I haven't checked the vacuum side yet)



I know this must be pissing off anyone following me (https://www.nopistons.com/forums/pub...1047683894.gif P'cola, 9BASE3, 13brv3), but please guys, don't leave me. If anything, it is a sign that I need help (in many ways!).



Anyway, to answer your question P'cola, I T'd into the hose that leads from the pressure-side TC solenoid to the TC actuator. I haven't checked the vacuum side yet.



I ran one more test: T'd into the vacuum hose right on the charge control valve (CCV). Here's what I got:



<5200rpm: 10"Hg (valve is definitely closed)

>5200rpm: 7.5psi (valve is definitely open)



So the CCV appears to be working fine.



So I think the only thing I haven't checked is the vacuum side of the TCA. I guess I'll check that, then simulate the same pressure and vacuum in the garage and make sure the actuator moves.



I haven't checked anything on the wastegate system either, but you guys seemed to think that wasn't the problem, so I'll save that for last.



What are the chances that this is all because I live at 7000ft above sea level? I started a thread on this at RX7club (I know some of you have seen it), but I never really came to any conclusion.



Thanks for sticking with me guys.

Man, I don't quite know what to say, beside lay off the crack https://www.nopistons.com/forums/pub...#>/biggrin.png



Well, the CRV sounds perfect. The TCA pressure side seems 500 RPM late, and the CCV is 700 late. That just seems strange, though I have not actually verified these RPM levels since mine is working. On the boost gauge, my transition is exactly at 4500, so I still can't explain why yours is late.



Does your primary boost drop before 4500? I know you said it dropped from 13 to 10 by 5500, but I wondered if it happened before 4500.



Look at your CCV position, then crank the car and look at it again. Did it really move? I seem to recall reading about someone who had their door sticking open, and the primary turbo was spinning the secondary in the wrong direction. When the secondary finally got kicked in, there was a lag before it got turned back around and started making boost. As you can tell, we're dipping into the wild and wacky theory reserve.



As strange as this all is, you may very well have more than one problem.



I'll keep thinking about this.



Rusty

This is a tough one to answer because when the primary is dropping things are moving very fast, and I'm mostly concerned with not wrecking the car https://www.nopistons.com/forums/pub...#>/biggrin.png . The primary boost does drop very smoothly, and it doesn't level out before transition, so I'm thinking it hits 10 very close to 5500. I'll pay closer attention the next time I drive. However, I don't think we should pay too much attention to the actual boost numbers because of the altitude (i.e., I don't know if primary should be 10 or 13, or somewhere between). I still don't have a good answer for what my boost pattern *should* be up here.







Ok. this is what the shop manual says too. The problem is, when I have everything together to start the car, I have a really hard time seeing the piston. Is there some trick...wait a minute, I just bought one of those little mirrors for checking the rats next - I'll try that.



Thanks Rusty



Because this might be getting confusing, I'm going to try and come up with a summary of everything I have done...and I have a new theory, which I'll get to later.

Ok, I have summarized things here:



http://www.geocities.com/laracers_vr_r1/bo...t_problems.html



I will paste all that into this thread for future reference once I get the problem solved.



Here's my current theory. and I think I might be getting pretty close with this one...



Precontrol is STILL not working. Why do I think this? Well, from TEST2 and TEST5 (see the webpage above) I now know the pressure on both sides of the CRV during prespool (3500 to 5200rpm). During this time the pressure is equal on both sides (0psi in hose going to the rats nest and 0psi in secondary side of the y-pipe) With equal pressure on each side, the CRV is CLOSED between 3500 and 5200. This is during pre-spool when it should be open. If the precontrol were working, there would be pressure on the secondary side of the y-pipe, which, with 0psi on the rats-nest side of the CRV, would cause the CRV to open. Thus, lack of precontrol => CRV not opening before 5200rpm.



what do you think guys?

I'm starting to think there's a reasonable amount of evidence to suggest that your secondary turbo is frozen up, and not spinning at all, though this wouldn't be the most common failure. Have you done one single test that shows the secondary is really producing boost? You've tested the crap out of the rest of the system, and everything works, but yet you still have no secondary boost.



Here's the logic sequence- at low rpms, boost a-plenty with just the primary. The prespool door opens, and starts bleeding off exhaust from the primary causing it to start loosing boost as rpms rise beyond 4500. The CCV opens (or not), and the TCA tries to put the secondary into full spool. Since the secondary isn't spinning, this causes a large drop in pressure, since you're only running on the primary turbo, and taking exhaust away from it to waste on the dead secondary turbo. Not the preferred way to go single :smirk:



What's the history of this car? Has it ever blown an apex seal in the past? That could certainly trash a turbo. Maybe the owner (assuming you're not the original owner) at the time didn't realize the turbo was damaged, or couldn't afford to replace them at the time. Heck, maybe the bearing is just bad. I think you'd have to remove the intake pipe on the secondary turbo to see if it spins freely.



How about this for a test- try to find a way to ty-wrap the CCV closed. Next, remove the CRV from the y-pipe hose. This should force any secondary boost to flow out the open pipe that would have gone to the CRV. I would think that you would be able to hear the boost coming out of this pipe if there is any, but I'd probably ty-wrap a piece of thin plastic wrap, over the end of the pipe for later proof of whether it produced any flow. I would NOT plug up the secondary with anything that can't be blown out if there is boost. Does anyone see anything unsafe about this proposed test?



Finally, if you prove that the turbo is free to rotate, I think you're going to have to throw in the towel, and pull that UIM for some complete testing. There's a reason Danny puts the hose job as one of the first items on his troubleshooting list. I tried to avoid doing it, but in the end, that's what fixed my problem.



As always, good luck,

All that makes alot of sense, unfortunately. The history of the car is that I'm the 4th owner, but it only has 21k miles. I paid dearly for that mileage, and I'll be pissed if the turbo really is busted (although I guess its my fault for not doing a thorough boost test when I bought it - lesson to potential buyers).



I'll check whether the 2nd turbo spins. It'll have to be tomorrow (or maybe just very late tonight).



Thanks again rusty.

I took off the inlet to the secondary compressor. I can see the blades using a mirror - they are all there https://www.nopistons.com/forums/pub...#>/biggrin.png . It spins ok. How freely should it spin? I can turn it with my fingers, but it doesn't keep spinning much (if any) after I let go (it's not on bearings, right?). There is a little play, but I hear that is normal. Is there anything else I should look for while I have access to the compressor?



I never checked the pills in the PC and wastegate. I need to do that next.

That sounds like a good turbo to me, but to be sure, maybe you should send those 21k turbos to me for some testing :smirk:



I can't believe you've made it this far without checking pills. What are we going to do with you :stickpoke:



From what I've read, leaving out the pills is a common mistake when changing hoses, but yours probably haven't been touched. I forget what year car you have, but later years didn't have pills. Instead, the restriction was built into the actuators. If the pills were removed, I think you'd be limited to 7 psi of boost, which is the spring pressure of the wategate actuator. Don't even think about asking me if the spring pressure changes with altitude https://www.nopistons.com/forums/pub...#>/biggrin.png



Not much to do now but suck it up, order some silicone or viton hose, and yank that UIM. In the end, it will be far less trouble than you've already gone through.

Did I mention that it will be FAR less trouble than you've already gone through https://www.nopistons.com/forums/pub...#>/biggrin.png



Rusty

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



And the funny thing is that despite this boost problem, the car feels REALLY fast. I mean, I would never have suspected a problem if I hadn't installed the boost gauge. Maybe the best fix is to remove the boost gauge https://www.nopistons.com/forums/pub...#>/biggrin.png .



I will check the pills today, I promise.



Looking at the results of my CRV T test, notice the pressure changes once at 3500rpm and then again at 5200. I think the 3500 change happens when the CR solenoid clicks (so I'm saying it clicks early, unlike everything else which clicks late). Since, after the solenoid clicks, the hose I T'd into is reading essentially the same as the secondary side of the y-pipe, the pressure is 0psi, and the change at 5200 is the change in y-pipe pressure at 5200 (from 0 to 7psi). Now, since 0psi after 3500 closes the CRV, that's not good for prespool. I don't see exactly how that causes the decline in primary boost (although fluid dynamics is a strange thing so it might lead to that). It could definitely cause the low secondary. But the late transition? I'm thinking that has to be caused by the same thing that clicks the CR solenoid early; a sensor for the computer?



I'm going to do what you said, which is to force the CRV open and check things out. If my theory is correct, I *should* see evidence of prespool in the secondary side of the y-pipe.



......and, I'm getting ready to order the hose. I have a thread going at the other place about whether silicone holds up over time. I'd really like some pretty colored hoses. But I don't have any good data points telling me that silicone won't disintigrate (like that silicone vs Viton vs rubber test that someone did) after a few years. Looks like it'll be boring (and expensive) old black Viton.



As always, thanks a bunch.