ATTN sequential gurus: I need your input on this rather discrete boost problem.
 

Well, I'm pretty stumped on this. I know the sequential I will first describe what happens, then I will describe what I think it may be. I am running the mods below with 12psi of boost. Thanks for your input in advance.:) (Especially to the sequential guys, dgeesaman, Rynberg, Kento, etc. who will probably respond to this thread;) )

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-I start boosting @ 2,800RPM, it quickly builds up to ~11psi by 3,000RPM and holds until transition.
-Slight dip to ~8psi at transition, but then right back up and holds at ~12psi with a slight taper towards redline.
-I shift into next gear, RPMS are above the transition point, it boosts ~12psi. I can do this until I run out of gears.
.....EVERYTHING works normally (for the most part)

BUT!

-I start boosting @ 2,800RPM, it quickly builds up to ~11psi by 3,000RPM and holds until transition.
-I pass the transition point, then shift into the next gear.
-Boost is at 2psi and holds constant @ ~3,000rpm. I will let go of the throttle for about 2-3 seconds to let vaccum build and rpms drop below 3,000rpm (at this point it should switch back to sequential mode), then I floor it but it still only builds up to 2psi.
-I just stay in the same gear for ~15 seconds, then it decides to boost normally again
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All of the check valves are in the correct position. The check valves are rather new. They are much like the ones that Dale Clark is selling, but only they are made of a different high-temp valve material.

My guess is that something is stuck open, allowing exhaust gasses to bypass the turbo at the low-rpm range after boosting past the transition point and shifting, thus causing only ~2psi of boost.

But what totally stumps me is why it takes so long to recover and boost normally again! Could it be that one of the intake hoses are collapsing? But why would it only collapse at low-rpms? Anyways, I'll stop here. I am going to diagnose this problem further when I have the time, but does anyone have any input on what they think it might be? Again, thanks for the input and for reading this length post.

(quick reference to turbo trouble shooting site: http://www.autosportracetech.com/RX-...erOverview.htm)

Start looking for patterns. When does this happen? Is the car hot? Is it cold? Does it happen going uphill? Downhill? Around a corner? Does it occur after aggressive driving (lots of boost) , or after you've babied it for a while (long periods of time without boost)?



Does the car make any strange sounds when this happens?


Good luck,
-s-

I dont think your problem has to do with any flow bypassing the turbo, as it really just cant do that. Your 2 psi means your are probably losing flow from the compressor. I would lean towards thinking your problem lies in the steps that are taken in going back from non-sequential to sequential operation. Perhaps in the process of going back to primary operation, the charge relief valve is opening up again (as it should), but the charge control actuator is staying open longer than it should, creating a leak. Didnt someone else in this forum have a similar problem recently?

I should add that if the charge control actuator is sticking open it probably isnt getting the vacuum that it should in primary operation immediately, in order to close (not an actuator problem). So maybe you have a sticking charge control solenoid or you are losing vacuum into that solenoid?

The actuators could be sticking, but it's much more likely that you have some solenoids sticking. Dave Disney's backpressure test, done with both vacuum and pressure in the reservoir, produces very useful results for sorting out the bad solenoids, IMO.

Dave

The wastegate bypasses the flow over the turbos.

Dave

Adding to this. I'll need more info but at this stage I would suspect the wastegate stuck open.

With the wastegate open, the engine can make around 2-psi on both turbo's & since you mention "2-PSI" that made me click.

Will require more info to "prove" this theory. Can you attach a vacum/boost to the actuator side of the wastegate control soleniod. Post back the info

Hi mate ive got a problem very similar to yours, my boost has you same symptoms, but my primary boost starts to boost correctly again after letting off the throttle for about 5 seconds. Some guy on here wrote a really good post about exact same symptoms,,, he found the problem to be a sticking solenoid controlling the turbo control actuator (the big actuator on the bottom of the turbos that requires both pressure and vacume),, he did tests and even recorded video of the actuator movemet,,, and found that the actuator wasnt closing after letting off the throttle,,, it wasnt closing because the air wasnt been aloud to bleed from the system because a solenoid was sticking closed. (he also noted ,, and ive noticed aswell that the exaust note sounds different when the actuator is stuck open)

I considered that, but how would that tiny WG limit the boost to only 2 psi?

The thing is, how would the wastegate remain open? If that were the case, wouldnt it need to be a WG actuator problem, since there is no way the actuator could be seeing enough pressure (7psi) in his situation. If the actuator were bad then he would obviously have the problem all the time, not just under the conditions he describes, which doesnt seem as likely.

There isn't much point in speculating what is wrong - the fact is that many components might be the cause. Tests need to be done to conquer/divide the system until the source(s) are found. I recommend using a Mityvac (the pressure/vacuum model 4030 is best), some 1/8" rubber tubing, and a tee to investigate with both static and road tests.

1) Check the wastegate, turbo control, and precontrol mechanical connections to see if it's hanging or sticking open. You'll have to get under the car and remove the turbo heat shields. I personally doubt this is the reason, since it would also preclude any primary boost.

2) "While you're in there", take a vacuum/pressure pump and pump pressure into the wastegate actuator. (Take two short sections of hose, one off each nipple, run them into a tee, and run the tee into the pressure pump and gauge). The rod should move steadily in/out as the pressure is applied, per FSM page F-90. As well, you might as well check the precontrol in the same way.

3) To verify the wastegate actuator is getting the correct pressure to it, tee into the top hose leading into the wastegate solenoid, and run it into the car, and put your boost or separate pressure gauge hooked up to that. Do a test run, and verify that it creates a fairly steady pressure (the gauge needle may jitter, but hold a certain value) whenever you are WOT above 4500rpm. If this isn't happening, either the solenoid is malfunctioning or getting a bad signal.

4) As for checking the turbo control actuator, it's a similar deal. You can tee into the light blue and medium blue w/ red dot lines right near the wg/pc solenoids. Again do a road test, you should see full vacuum and full pressure come on and hold at 4500rpm. You can also tee in there to verify that the actuator moves at the right pressure per FSM page F-86.

5) The charge control input can be verified by teeing into the line leading out the top of solenoid F (green/yellow dot). It should snap to full vacuum at 4500rpm. Test the actuator itself by page F-87.

6) The charge relief should also be tested per page F-88.

Reference the vacuum hose diagram here, and the FSM available here.

Yeah there could be a few things which might explain this, but I would start with things in order of likelihood. The input to the CCA being a possibility, as a first step I would T into the input and not only look at whether it gets vacuum with the key turned on, but OBSERVE it with a boost gauge from inside the car when you repeat the experiment you described. Check to make sure that when you shift, and the rpms drop to 3000 or so that you say, that the line to the charge control actuator goes immediately to vacuum.

There is no specific pattern where this happens, it happens very consistently. I don't know if I would venture to say that something like the turbo pre-control gate is open when it shouldn't be or any other actuator controlled gate, as I do not hear the "choking duck" sound. But then again, I could just be blowing smoke out of my ass

I will check the CRV to see if it operates within spec, but I would doubt that it's not operational. I would agree on checking the CCA and solenoid, as it could be leaking boost and allowing it to bypass out of the CRV, but wouldn't it then get 0psi as it would be releasing all the boost? Anyways, I guess I'll have to do more diagnosing before I should come to any conclusions.

Also, does anyone know how to get a regular MityVac (plastic, non-silverline) to create pressure?

A precontrol problem couldnt get you only 2 psi in primary operation (the precontrol opening is too tiny). A long time ago I once t-ed into the the nipple on the y pipe on the secondary side to oberve the boost seen during prespool as the secondary turbo was venting, and it was not zero, but closer to 2-3 psi from what I recall...the small opening of the CRV provided enough of a bottleneck to allow the y pipe on that side to be slightly pressurized during prespool. If you have a boost gauge in the car I would just connect it to the CCA and see what you get, before forking out money for the MityVac (from Sears?).

I don't understand what readings I should get (if it were functioning properly). Can you elaborate?

I already have a MityVAC from my previous turbo problem last year. Only, the MityVAC is not the Silver Line, it's the standard plastic white one.

I would consider myself somewhat familiar with the sequential system from my sequential adventures of the past, and the best advice I gave to someone was to check everything. I think I should follow suit prior to making any assumptions.:rlaugh:

You should just be able to switch the line and the cap. The issue is that you won't be able to read the pressure off the Mityvac - you'll have to hook up a pressure gauge in line.

Dave

I'm a simple kind of guy, but I noticed in your mods that you don't show anything for upgrading the stock accordian intake hoses. A puncture in either of these hoses can yield the same results. From my first-hand experience, sometimes they won't collapse, sometimes they will. (i.e. sometimes you get boost, sometimes you don't (2psi) )

I had a VERY similar problem with mine if not the same. One simple thing to check (which I found by accident) is the coil packs and spark plug wires. I had a broken leading coil pack which after i replaced it, it worked perfectly. I know of a couple other rx's had the same problem. But like you said, sometimes it worked and sometimes it didn't. And mine dropped down to 2psi like your's does.

-David

I agree with Aristo.
When I read the first post, I was thinking something to do with CRV / CCA.
I would re-check your one way valves. I think I had similar problem back when (2-3 years ago) and everytime it was either bad one way or switched lines.

Good luck and let us know what the problem was.

Oh sorry. So, with your boost gauge t-ed into the input to the charge control actuator, drive at say 2500 rpms and floor it. The value on the boost gauge should be the vacuum in your vacuum system (around -17 inHg) until 4500 rpms at which time it should jump to whatever your secondary boost is set to. As soon as you get into secondary operation shift and let the rpms drop as you did when your problem arose. When the rpms drop back to the 3k range the gauge should go right back into vacuum if the charge control is working properly (ie the CC valve should close again). If you could find out if this is happening I think it might be helpful.

WOW! Great diagnostic method!!

One thought I was having was one from Dave Disney when he had solenoids that did not operate over ~10psi. I am begining to think my solenoids are the weakpoint in the system as Dave Disney observed. I am now running ~12PSI, 20% over the stock amount of boost. Does anyone remember the name/link to that thread? I tried searching, but I even forgot his screen name.

[edit] I think I may have found it. I will test my solenoids for this problem that Dave Disney (autoxer) had, as I did not develop this problem until I turned up the boost.
https://www.rx7club.com/showthread.p...4&page=2&pp=15
http://rx7.voodoobox.net/howto/solen...oid_check.html

This doesn't seem like an actuator problem, as I have tried lubing and operating my actuators. I think the problem really lies in my actuators. I will find out by turning down the boost pressure. I will update you guys as soon as I get some time to fool around with it.

Quick question, though: If I disconnect the wastegate solenoid, it will limit my boost to 7psi across the range, correct? (I dont want to mess with my manual boost controller)
[/edit]

UPDATE!

It seems that the problem does lie in the increased amount of boost. I turned it down to 9psi and it doesn't have the problem. I turned it to ~10PSI, and the problem worsens a bit.

Now, I was thinking: if I were to boost ~12PSI on the STOCK IC, wouldn't the solenoids be seeing 14PSI+ since the stock IC has a 2PSI drop pressure @ 10PSI? I think if my solenoids were seeing that much boost, I would understand why they are sticking open.

I fixed it!
Not to mention I got my turbos to spool faster than ever @ 13PSI. I will do an extensive write-up on this solution once I get some time off work. Again, long live the sequential-twins!:bigthumb:

Looking forward to hearing the rest of the story . . .