Okay, my phone is acting funny so this might be a double post.

If I try to build boost after 4500rpm it momentarily goes up to 2-3 and then drops to 0-1. So yeah....

Now that my turbos are nice and hot I'm going to try and take them off to see if I can find a problem there. I literally don't know what else to do at this point.

As always, thanks for the help and keep the ideas coming!

Sorry to say that's probably what I'd do as well. Maybe others will have another big idea. Very frustrating.

Still... I think it would be odd for a turbo hot side to fail without an engine blowing and throwing a seal at it.

I might throw a spare wastegate actuator on it before pulling the turbos completely. I think I have one if you need it. Can't remember if you tested WG actuator on the car by hooking up mityvac but it should open around 7psi with the second port plugged.

I am surprised you were ever able to control boost to 10 psi without a main cat. I've always heard that was an issue due to WG getting overwhelmed with flow.

Got down to the turbos today but they are still on. I need to disconnect the oil and coolant lines and then unbolt the turbos and that will be it. The one bolt on the downpipe probably took two hours alone to get off, and now it needs to be replaced. I tested both wastegate and pre-control actuators and they both move at 7 psi. Hopefully I'll know something by tomorrow.

Well I got the turbos off and I didn't find anything disconnected or obviously broken so I don't know any more than I used to. One of the gaskets between the turbos and the engine is a little bit broken but I don't think it's the issue. Hopefully you'll look at the pictures and immediately see the problem and explain.

Here are some questions: If my turbo control valve or my CCV didn't open, what would be the results? I've done a bunch of block off plates, if one of them had developed a leak could this cause my issue? I figured I would have different problems than this.





Any ideas? I hope so, I'm all out.




Thanks again!


https://cimg4.ibsrv.net/gimg/www.rx7...4a67a8b2c.jpeg
https://cimg6.ibsrv.net/gimg/www.rx7...9b8d43a05.jpeg
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Did you check the wastegate flapper? Not sure you can see it without cracking the turbos in half.

If you are truly inspecting the turbos you are also going to want to look for turbine damage. You can't see that from outside... In fact, it's difficult to see even when you crack the twins in half. They get damaged down at the base of the turbine, which is shrouded by the hot side snail.

Is there any chance something went thru these turbos... like an apex seal?

"Here are some questions: If my turbo control valve or my CCV didn't open, what would be the results?"

Bad secondary boost... but you tested all that, right? If you doubt it you can always throw a go pro and flashlight under the hood to see what's going on during a drive.

The flapper looks good. The blades look good. One gasket is a little torn.

I did test valves, I'm just out of ideas and an grasping at straws. I guess I'll crack open the turbos tomorrow but I have low hopes of finding my problem.
https://cimg0.ibsrv.net/gimg/www.rx7...0d3a4843d.jpeg

You can get a good look at the exhaust turbine wheels with an endoscopic camera. Should be pretty cheap online. Any major damage from a foreign object should present itself pretty clearly (check my exhaust turbine post, and you can see how I know this).

I'm going to continue being a broken record and recommend you block off/plug your exhaust ports and pressure test the rest of your system. You're chasing down a deep rabbit hole right now, and as far as I can tell you never did this basic check to see if there were any leaks. I can't stress how obvious this will make any boost leaks to you. I'd continue to do this test as you re attach the turbos, and other major intake components, as things may show up that you didn't catch before as you put everything back together (go ahead and ask me how I know). Even if this doesn't turn up *the* issue, its going to save you some headaches that will come up after you do fix this issue.

I would personally not reuse the turbo -> exhaust manifold gaskets simply because it will be a PITA to have to take the turbo down and replace them if they do not seal correctly after re-assembly. The engine block -> exhaust manifold gaskets should be reusable, but I replaced them too for the same reason. I'd 100% replace the 4 gaskets for the turbo oil lines.

I also wouldn't reuse the nuts you removed taking the turbo down. Get some good exhaust nuts, or get replacement OEM nuts. I'd use high temp anti-seize on them, though I am not sure it will hold up to the turbo heat.

You should be able to bench test the CCV by applying vacuum to the actuator. If it works correctly, then it shouldn't be getting stuck (and you mentioned you knew its getting vacuum at the correct time in an earlier post, but you could double check that too)

I'd also check if you hear any noise when you rotate the secondary turbine by hand.

Based on the fact you did audibly hear something that seemed unusual to you when the secondary kicked on, its either leaking/venting somewhere in a major way, or the turbine is damaged. If you verify no damage and no boost/vacuum leaks, you will have a much smaller cross section of things to check out.

I sympathize, this kind of troubleshooting is not fun, it's just a painful process of elimination.

I tried a boost leak test but the results were inconclusive. I don't have a big compressor, just a tire inflater. So it runs until pressure is built up. I hooked it up and never built pressure. I didn't hear a leak over the sound of the pump. I sprayed done soapy water on all the connections and made no bubbles. That's where that stands.

I was going to get new gaskets already but new bolts is also a good idea. Both turbos spin freely and look good. I measured boost from the second turbo at the aft most line on the extension to the y-pipe and it makes boost, it just goes somewhere else at 4500rpm.

I was looking over all I've done because I figured I must be the problem so I probably missed something and sure enough I forgot to check the control solonoid for the CCV. Don't know how, must have been tired. Either I forgot to check it out I forgot to write down my results. If that's the problem than the CCV wouldn't open and the boost would vent out the CRV. But I capped that so where would it go? I don't know. Back fill the turbo and choke it? Is that my whooshing sound? Or is that a crazy idea? It sounds the same if the CRV is capped or not and that shouldn't be the case.

Any ideas?

I don't think a typical tire compressor is going to cut it. Firstly like you said its loud so you can't hear any leaks, and secondly its probably not going to build pressure at all, if there is any leak.

The cheap 5 gallon I bought off Amazon can pressurize my system for a few minutes before it empties the tank, for reference (and I blocked off my exhaust to help make building pressure easier). With actual pressurized air, you will definitely hear any medium to large leaks, and you'll see them with the soapy water too. I don't think a tire compressor will help you at all.

Depending on how you capped the CRV, air could still make it through. I'm not sure a zip tie + rubber cap would actually seal it under boost pressure. I would definitely check out that solenoid though, and apply vacuum to the actuator on the Y-pipe to double check it operates smoothly.

This thread has some good information/troubleshooting for the CCV/CRV:
https://www.rx7club.com/3rd-generati...oblems-295830/

I'm not 100% sure, but if the CCV wasn't opening (bad solenoid?), I don't think all of your boost could leak out of the CRV.

Could be that your CRV has an issue.

If the CCV is opening, but the CRV is also remaining open, it seems like on paper at least, all your boost could go out the CRV. I'd think you would have noticed that pretty quickly though.

Turbos: Just confirming... you disassembled further than the pictures show and checked the hidden wastegate flapper on the primary and the turbine condition on the secondary?

CCV: I thought you teed into the line and confirmed vacuum/boost at the correct times? I also thought you wired the CCV open and capped the CRV/BOV.

SpinningDorito, I'm pretty sure the CRV works. I've pulled it off and checked that it works using a Mityvac and I've Teed into the line to make sure it's getting the proper pressure, 0 until 4500rpm and then 6-7 psi. It's possible that a cap and a zip tie couldn't hold all boost but I don't see how all of my boost could escape and not either blow off the cap or crack it or put a hole in it or, at the very least, sound different.

Alex, you're right. I did plug in and see that it's values were correct and I assume those could only be correct it the control solonoid (F) was working. So going after that won't tell me anything new. Also, I did wire the CCV open and the CRV and BOV closed(capped)and that didn't help. Last night I was tired and frustrated and just going over my notes and found a missing step. So, if it's not that.... What?

Here's a picture of the pre-control flap, looks good to me. I can see the wastegate but can't get a good picture of it. I open it with pressure and it looks fine. Also I don't have any primary boost problems which happen with wastegate issues.

I'm totally out of ideas. The only thing I can see right now I'd that my very first question was never answered in a way that I understood back then which would have had me do a few more tests. But that doesn't help me now. Any thoughts? Am I too stupid? Sell the car and buy a Yaris?
https://cimg9.ibsrv.net/gimg/www.rx7...a231822ef.jpeg

Turbos look good with minimal cracking. I assume both turbos can spin freely and smoothly?

Easy access to the turbo control actuator on the exhaust manifold - get a Mityvac and make sure it holds vacuum. You may have already done this previously, but if you hook to the vacuum side of the actuator you should be able to see the door in the exhaust manifold move.

That one gasket with the minor blow out wouldn't have been a problem but it's worth replacing while you're in there, get it now before it actually does fail on you.

Also worth checking the fit of the Y-pipe with the turbos off - make sure it sits flat on the 2 flanges and isn't getting cocked to one side.

Dale

Dale, both turbos spin freely. The turbo actuator holds vacuum and moves. The y-pipe connects flush with the turbo compressor housing.

I really don't know at this point. I'm thinking of taking off the UIM again just because I don't know what else to do. I'm just staring at the car and questioning my life choices.

My last idea is to put it all back together and take it to a dyno and try and recreate the problem and then follow it back to the source. I'm open to other suggestions.

The pre-control is used to control primary boost. It dumps the excess exhaust gas over the secondary turbine to pre-spool it. The wastegate is used to control boost after transition. You are correct that if the wastegate was missing/open you would probably have primary boost issues as well...

But you have the turbos off to check everything... so check everything. Wastegate, turbines. Just because you can see the turbine doesn't mean you can see where the damage is on it. You need an endoscope to really inspect it unless you take more of the turbos apart.

The initital question was about teeing into the line on your y pipe that comes before the charge control butterfly. It's an interesting test because you're seeing if the secondary is building pressure pre-transition. That's assuming it can build pressure even though the relief is open... I've never used that test before so I don't know what the results should be. In that case extension manifold means your UIM. So you're comparing the isolated secondary side to your manifold boost pressure. Seems like a weird / convoluted way to test everything. But if you capped off the CRV and put a tee/gauge on the nipple before the butterfly that test will tell you if/how much your secondary is pre-spooling.

https://www.rx7club.com/3rd-generati...tified-841821/

If your turbos are mechanically sound, then you have a control system issue that hasn't been tested properly or a boost leak that presents as a secondary pressure issue.

Alex, the wastegate controls boost after the transition by opening that port in the turbine side of the turbos allowing exhaust has to bypass/bleed away from both turbines. That makes them slow which then slows the compressors and controls boost. If the wastegate was leaking this would happen even when only the primary was operating causing primary boost issues. I understand my first question now but didn't then. As a result I didn't test the boost the second turbo makes before the transition. I thought I had but now that I have it all apart I see I was wrong. I still feel like it makes boost since the turbines spin. Maybe, somehow, the shaft between the turbines broke in a way that allows them to still spin from contact but stops under load? I can test this when I get home but that's a pretty crazy idea.

I'm torn between continuing looking for the problem and just going single turbo. Honestly it's just pride that I can "fix" this that's keeping me going.

I was already aware of how a wastegate works, but thank you for the explanation. See revised post above.

Alex, I'm sorry. I don't know how I misread your post but I sure did. I must be too worked up over this car. That's a poor escuse I know. I think I need to take a little time off. Thank you for all the help you've given me and for keeping your cool.

At this point, I'd still suggest to re-assemble and pressure test as you re-assemble. I'd replace all the gaskets, unless you know they are fairly new.

If you can do that with no/minimal leaks detected, then you know it's an issue with the control system somewhere, as you've eliminated most all other possibilities.

Also, don't do any of the work while you are frustrated. That's a surefire way to overlook something.

I've been contacted by several people who found this thread and want to know if I ever figured it out. Well...

I checked every vacuum line, solenoid, pressure vessel and never found out what was wrong. I had lots on internet help(as you have read) and nobody could help me. After another day of failure I realized that I must have missed something. So I had to start over. Then, even if I figured it out, I was worried that if something ever failed again I would have to do this whole process over. That was when I went single turbo. I'm sorry I can't tell you what the problem is. What I can tell you is that I love my single turbo and I don't consider it a failure at all.

Thank you for updating this thread. I've been chasing secondary turbo issues since this summer (when time permits) to no avail. I've read every post I could find related to this issue and many of these threads end in no conclusive resolution. Interesting that there are still people out there chasing a nice sequential boost pattern on a 30 year old car. I've performed every test, replaced solenoids, double traced and tee'd into every vacuum line and I'm nearing the point of removing the twins to inspect.

My initial goal was to get the sequentials running properly and enjoy a close to stock FD for a while. However, thoughts of going single turbo are starting to creep into my head. Especially when I think of threads where guys state they've been chasing sequential boost issues for YEARS ! I'll probably go back and double check everything (again) and update if I find my issue. Glad you are enjoying your car now.

Never figured out why people have such a hard time with this. Narrow each system down, see if it is working like it should, on to the next. Charge control, charge relief, turbo control - that's it.

Dale

Hi Dale, to be fair there are a good amount of threads with a resolution and its usually something simple which was missed (or uncovered) in the testing steps, like a bad solenoid, backwards check valve, incorrect vacuum line routing, disconnected actuator rod. In these cases yes, the troubleshooting is easy enough once you have a grasp of how the system works, and the solutions are relatively easy fixes.

But there are several that go past that stage, like the OP in this thread. I'm in a similar spot. There's not much information available for issues after the suggested tests have been tried and those 3 systems have been seemingly verified as working properly. Of course I'll have to go back and check everything again up to this point, which is PITA but still within reason. The next logical step seems to point towards electrical (harness or ECU) or mechanical failures (cracked manifold / leaking gaskets), at which point its no longer a simple fix and going to a single turbo becomes a reasonable option. I'd be pretty upset if I were to go ahead and remove the turbos, inspect, reinstall only to potentially revisit the same issue.

If the charge control, charge relief, turbo control systems are working properly, there are a couple of other things that could still potentially cause loss of boost at transition. I'm not sure how likely these scenarios are:
- boost leak which presents such that you get 10psi primary, and 0 or low pressure secondary - seems unlikely but still possible?
- exhaust leak - the turbo to manifold gasket is separated primary from secondary, possible to loose exhaust pressure at transition only? read one case where the access door to the precontrol flapper was leaking exhaust which would cause the same problem.
- ECU issue - read a case where a bad PFC was the cause of someone's secondary issues.
- damaged second turbo - easily verifiable

Anyone else perform all the recommended tests and come up short? Or run into any of the issues above?

Wow, so much action on a dead post!

My intention was not to end on a "Abandon all hope ye who enter here" feel. Dale is right. Every issue on every car ever, can be tracked down, identified, and resolved. It all comes down to what it is worth to you. My point was that I had already hit this point brought up by rx7_nyc:

After that I had two choices. One, start all over again and find what I missed. This would give me a working 30 year old vacuum system that I would constantly worry about failing and forcing me to start over that still gets walked by the neighbors new Accord or, two, switch to a new modern single turbo that is simpler, more reliable, and makes more power. For me, the second option was the one that was most attractive. I was in a position were I could do it and plunged in. Now, after a year driving the car more than I ever did before, I am able to report that I am extremely happy with the results and have no regrets. Do what works for you. I just wanted to share the end of my tale.

Good luck rx7 _nyc! If you need any old vacuum or turbo parts, let me know. I got a box full!

I've had my car since 2004 and have put about 80,000 miles on the car myself. In that time I have had ONE turbo control system issue, a turbo control door solenoid would stick. That's it.

What's the secret?

- Always be vigilant about boost leaks. Make sure all the couplers are tight and you don't have leaks.
- Replace crap OEM parts. The 2.75" coupler on the Y-pipe needs a silicone replacement, Viton check valves, silicone hose, silicone hoses to the CRV and ABV.
- Get that vacuum diagram out when you put things back together. Triple-check the connections. SUPER easy to get two hoses swapped. Had a friend who drove around for years with the hose for the EGR valve and the CRV swapped. 5 seconds with the diagram when hooking it up will solve that.

Dale