Where did all my boost go? - sequential troubleshooting
 

In my efforts to track down my boost issues, I've performed the following:

Brand new solenoids (all of them)
Four new check valves (thanks Dale!)

My problem has remained largely unchanged, however. I figured based on search results that I should replace the solenoids and check valves anyway, just for good measure.

Primary boost is excellent down low, however, as the RPMs climb, my boost will drop suddenly and drastically, and struggle to climb back up (but never reach) where it was. The engine noise also seems to change pitch.

However, if I accel off and give it time to let the RPMs drop, I will have immediate boost again.

Cruising and going into the throttle I have no issues building boost either, it seems to be related to high rpm and the changeover process?

The shop that did the work is familiar with FDs, and you can see the picture below the check valves replaced, and the one that was left alone. I'm assuming this was done correctly as far as the check valves go, as Dale mentioned to only change the green/white and Green/Black.

Anyone have any suggestions on where to pursue this problem further in terms of troubleshooting?
https://cimg6.ibsrv.net/gimg/www.rx7...a6128d9245.jpg

I had a similar issue when I first got my car on the road. It would intermittently have no boost at the transition and make a Ric Flair "whoo" noise.

Turned out to be the actuator on the front part of the manifold with 2 Hoses hooked to it. It would hold one way but not the other due to a failed diaphragm. Pretty easy to test with the car on ramps.

Vince

If you can, maybe double check the crossover tube connection from the y-pipe turbo going to the intercooler, make sure nothing is torn. In my case I had a similar issue that you had described, however it turned out the connection between the y-pipe and the intercooler had a huge hole in it causing a massive boost leak, may be worth looking into.

That said however, also take a look at the vacuum chamber, you could potentially have either a faulty one way check valve going to the vacuum chamber, Or the vacuum chamber itself is no longer holding vacuum?

So I would first check the check-valves if you haven't already as it might be a good place to start.

I'm sure other members with more experience than I have can probably chime in with their thoughts and wisdom on this issue.

Take your time, don't rush anything and good luck with finding the issue!!

Glad you got the check valves!

There's one that is typically under that pressure tank there, did they get that one swapped out?

Do you have a boost gauge?

Most likely the problem with be the turbo control actuator. As stated above, some have blown diaphragms and if so the turbo control door either won't open or will open slowly or partly. This is a large can mounted to the exhaust manifold, you can get to it under the car (kinda). It has 2 ports, one pressure, one vacuum.

Probably worth doing a simple test on it to make sure it's good before diving into the solenoids. disconnect the 2 hoses going to it, push the rod in, put your finger over one port, and the rod shouldn't go all the way home until you take your finger off. This should be true on both ports.

Dale

I do indeed have a boost gauge, but it's in kpa. Not that it is an issue being in that measurement. I believe it reads about .7-.8 kpa max boost before the issue starts. When the issue happens it will snap below .5 (how low I'm not sure, but its not zero.) and then will struggle to slowly build back up (but never reach) .7-.8.

That engine sound change is noticeable, too. It's almost like the motor made a change to an N/A exhaust note (even though I have boost. Boost struggling to build when this happens, but boost nonetheless.

The Rotary tech (I wish I could work on my own cars here) did all the solenoids and the check valves, except what I'm assuming in the picture is the one Dale mentioned to not change, as the tech told me there were four check vales I dropped off (that Dale sent) and five that were on the car, so he left the odd ball one (in the picture) unchanged, and did the others.

I'll look into the turbo control actuator this weekend, How much play is considered too much? I know you mentioned it shouldn't go all the way back home with my finger over one of the two holes, and to test them both, but I was making sure there wasn't an allowable margin.

Edit: I will double check under the pressure tank to make sure it was changed.

I did some verification later today to confirm when exactly this happens. The whole thing starts right about 4500 RPMs

4500 RPM is the normal transition point.

Stock boost is .7 kpa. Stock boost pattern will be .7 to .55 or so at transition then back to .7. You could also have a minor boost leak as well.

On the TCA, it's not as much play as just verifying the diaphragm isn't torn. WIth your finger over one port it shouldn't be able to go all the way back home.

Are you in an apartment or something that forbids working on cars? Sounds like you need to make an off-site buddy with a driveway you can do some work at :).

Dale

Basically. Rather annoying not being able to work on my own car.

Definitely not the normal 10-8-10 boost pattern (or .7 - .55 - .7 since I'm talking Kpa here.) Boost will plummet to a few kpa. Not zero, but low, and will struggle to build back up and not reach .7.

I've considered the possibility of a boost leak, but it boosts absolutely fine on the primary. I can't think of any issues as long as I stay below 4500. Theoretically, that would mean I shouldn't have a boost leak, because the entire system is charged when it's just the primary operating, and I'm not having any issues there, correct?

I've tried searching for a TCA (should I need a new one) and I can't find anything. "Turbo Control Actuator" hasn't gotten me anywhere as far as search queries go, is there something I'm missing?


Thank you guys for the insight so far.

You could have a boost leak on the secondary side - the small hoses that go to the charge relief valve are prone to leaking/cracking/getting hard.

I wouldn't just buy a TCA unless you KNOW it's bad. It's not a hard test to do and it's a pretty solid "this is good/this is bad" answer. Just stinks getting TO it to test, it has to be done under the car.

If you DO need one, PM one of the guys that sells parts like FritzFlynn or Tomsn16 they will possibly have a good one.

Dale

Do you happen to know what size & Length hose I need for the charge relief valve?

Minor update - I looked at the charge relief valve today, and while I didn't pull every hose off and look into it, they all looked cosmetically fine. No obvious signs of cracking or missing clamps.

+1 to checking turbo control actuator. Mine has been acting up since the 99 spec turbos were installed. Frickin annoying.

The various ~1" diameter hoses on the Y-pipe for the charge control and blowoff can't really be diagnosed by looking. With the clamp on a crack can easily hide and many times they are so hard that they simply don't seal even clamped down.

I found silicone replacements for those hoses a while back, search around on my old posts. They were reasonably priced, fit great, and have stood the test of time on my car.

Dale

I'll have to look into that.

As a minor update, I did look at the couplers to make sure there wasn't a boost leak, the crossover pipe actually has a new-ish looking Greddy coupler there. I've ordered a new TCA (mine looked pretty grungy, but thats besides the point) and I'll look into the hoses as well. Eventually I'll run out of things to inspect/replace. At this point I'm considering it all preventative maintenance.

Edit: Dale, I tried searching by your username specifically, but my terms might not have been close enough, any suggestions on what I should tailor my query to?

I just ordered replacement silicone hoses for my CRV & ABV (BOV) based on Dale's recommendation... the link in his old post on Amazon was out of stock so I sourced them through Pegasus:

https://www.pegasusautoracing.com/pr...sp?RecID=11046
https://www.pegasusautoracing.com/pr...sp?RecID=12998

Just cut them down to size with a razer blade however you want and you're good. Working great and they seem to seal well even without tightening clamps on them (still put them on but had some loose when I did some boost leak testing and they didn't leak)..

Yep, here's the 90 degree hose -

https://hpsperformanceproducts.com/p...lack-blue-19mm

HPS is who makes the one I bought, I got a black version. The 3/4" ID is what you want, that fits great.

I would also get some Norma-Torro hose clamps as well. They tighten up on that hose great and won't cut the silicone.

FYI here's the original post I'm referring to -

https://www.rx7club.com/3rd-generati...valve-1060209/

I Googled "90 degree silicone hose daleclark site:rx7club.com" and it was the first hit. Use Google to search, the forum's search sucks most times.

Dale

Awesome, thanks Dale! That should do the CRV hose nicely. I know you mentioned the charge control and blow off hoses as well, but I'm curious as to how much approximately I would need length wise, as their site offers a few different variants.

Just measure with measuring tape and see how much you need. It is going to be different if you have a stock intake or aftermarket intake.

That 90 degree hose I ordered had long legs on each side, I cut those off and was able to use those as well.

Dale

My car is completely stock, I suppose I can just measure the BOV/CRV hoses. Those should be the only other ones I'd need in that size, correct?

Yeah, that's the only hoses to worry about. The air pump hoses I think are the same size but they typically don't crack and get crappy.

Dale

Well, the TCA was replaced, and the problem persists (at this point, like I mentioned above, I'm considering this preventative maintenance. What I fix now is less issues to crop up later. The car's 26 years old, so I don't see an issue with overhauling all these components anyway.) I think all I have left are the hoses on the secondary side, like the one going from the CCV and the ones from the BOV/CRV.

Edit:

Just to recap (for the sake of possibly helping someone else down the line)

Work that has been done:

Replaced all solenoids w/new OEM
Replaced all check vales w/DaleClark specials
Replaced Turbo Control Actuator with known good actuator.

What's left to do:

Replace Hoses on Charge Relief Valve (CRV), Charge Control Valve (CCV), and factory BOV.

The hose was mostly out of stock online, unfortunately, but I did find a local hose supplier that had what I needed.

Thanks to DaleClark pointing me in the right direction, I sourced two pieces of silicone hose with the 3/4" inner diameter and a 90 degree bend.

The other hose (rather than risk getting not enough) I just grabbed six foot of 3/4" inner diameter straight silicone hose.

It will likely be tomorrow by the time I get to replacing the hoses, as its stupid hot right now and I'm not keen on burning myself.

We sure it's not like an old thread where the guy had clogged his catalytic converter??? I'm getting Deja vu.

I have had my BOV/CRV hoses leak they usually pop them straight off and make the rick flair wooooo or whistle/screams at you. If your on stock intake box it might hide the noise.
I tightened down some hose clamps and it went away. Roll your windows down and boost away you can't miss it.

The only real audible difference is at the changeover at 4500, the engine exhaust note sounds louder, and almost Non turbo at that point (though it is still attempting to and building a small amount of boost) if that makes sense.

So I did some testing today after the TCA was replaced, it looks like it's become slightly more consistent. I did a few pulls, and I'm seeing 10 psi on the primary turbo. When transition happens it drops down to about 2 psi, then builds up to and holds at 7~ psi, though the buildup is slow.

Anyone have any ideas?

Thought I would post an update here until I have a chance to get to the CRV & CCV, as well as their hoses for inspection.

Do you still have a catalytic converter? Maybe it's clogged.

Vince

That did cross my mind, but if the cat was/is clogged, wouldn't it choke under heavy load all the time, not just with the secondary turbo?

Edit: My car is also a JDM FD, so I do not have a precat.

Only time I had an issue like this was crack in my crv hose. I didn't go the silicone route yet, but I will eventually get around to it. I grabbed a quick hose from parts store with the proper bend, cut, installed, and issue went away.
only other boost issues I can remember now are the couplings for the ic which I just bought new, high quality hump hoses and new clamps. Keep us posted l.

It's possible that is is broken up maybe. You can easily confirm this by banging on the converter shell when it's cold to see if it rattles.

Other possibilities are the double solenoid that is bolted to the UIM where you can see it or there is one in the rat nest marked F If I recall correctly.

When I reassembled my long block, I followed a guide on here that walked you thru testing all the solenoids. But basically you put them on a cookie sheet in the oven at 250 to simulate underhood temperatures. Then you tested it with a mighty vacuum to check for leakage, then applied power with a 9V battery to be sure it operates.

I found one bad one in my setup and one that was just broken.

There are a few other things that could be wrong, but you'll have work your way thru all the parts. The butterfly in the y pipe could be sticking, the CRV could be leaking among others.

Keep us posted on your findings,
Vince

The solenoids are all brand new. While I wouldn't rule out the possibility of a DOA one, I suppose it doesn't hurt to keep that in mind. I'll be replacing the CRV, CCV, and BOV hoses with some new silicone I bought, the plan is to test those during the process.

I actually did have a moment. I'm sure I mentioned this, but if I haven't, the car has a PFC, and has had one since before it came over on the boat from Japan. All I have is the Commander. While I doubt they would deliberately tune it to act this way, I was curious as to if maybe there could be something PFC related that got changed?

• It's easy to pressure test the intake piping so I'd just do it.. (I wish I did this earlier when I was troubleshooting my car as it rooted out a couple issues). Yes, if you are getting 10 psi on your primary, you likely don't have big leaks. However, by doing this you can verify your ABV and CRV and new silicone hoses are good. If you test over ~7psi, you need to apply some pressure to the reference ports of them so they hold higher pressures otherwise they start mooing like a cow and letting air through. Go to Lowes/Wilco and grab a couple of test caps.. you can use these to cap off the primary and secondary inlets to easily test things: 2" test caps
• Another good test is to manually put pressure into your WG and precontrol actuators to test that they move at ~7psi. If not, there is an issue. Because your primary boost is good and then it bogs at the transition, it makes me think the secondary turbo is not getting spooled up or something. You might be able to even test your WG/precontrol solenoids here by putting pressure on the inlet side of them and then energizing them (I'm a little fuzzy on this as I replaced my stock solenoids with MAC valves). You can also do this to the CCA actuator.
• To test more of the complete system, you can then manually put pressure in the pressure tank and vacuum in the vacuum tank using a Mityvac/bike air pump and then energize a solenoid and check that the corresponding actuator moves. For example, even with the car off but ignition on, I believe if you put vacuum in the vac tank, the CCA arm should suck itself in. If you then energize that valve, it should release (you can also just verify this by looking at the actuator when the car is idling, it should be sucked in). Make sure you have both pressure and vacuum in the tanks and you energize both TCA solenoids (there's one for vacuum and one for pressure) to test the TCA. You do have to study and understand the solenoid control system to know how they should be behaving and which solenoid(s) to energize.

If you try a bunch of these things and don't find anything and suspect maybe an issue with the turbos, you can always wire them to be non-sequential temporarily and verify you are getting good response and boost in non-sequential mode.

Good luck!

Sounds like you had similar issue that I had when I had twin. I know this probably a wild crap shoot, have you tried looking into you wastegate and pre-control connection? Sounds like your pre-control signal is going into the wastegate and wastegate signal going into the pre-control.

https://cimg5.ibsrv.net/gimg/www.rx7...ff8c61deef.png
On your WG and Pre-Control, there is a white dot, white DOT on the harness goes into white DOT solenoid.

A slight update,

All of my replacement parts have arrived, so at this point once I've replaced the Vacuum & Pressure tanks, the CCV, and the CRV, as well as the 3/4" hoses that go to them, I will have basically run out of parts to fix. I'm not typically the one to just throw money and parts at something until it sticks, but the car has 52,000~ miles on it, so I imagine it's spent a lot of time in a garage, and not a ton being driven. At this point I'm replacing everything on the sequential system with new/known good components and considering it preventative maintenance.

The last parts have arrived (thanks to the forum members, you know who you are) and I'll hopefully have this done by next week.


https://cimg1.ibsrv.net/gimg/www.rx7...4bcb7bcb89.jpg

Seems autosport racetech thing has disappeared sometime in the last few years, which had a good troubleshooting guide. Hard to believe this was back in 2008! https://www.rx7club.com/3rd-generati...-stuff-802060/ That's a comprehensive way to test everything. There's a non zero number of solenoids that are defective out of the box, so wouldn't necessarily trust everything to be perfect.

Was in the fortunate position to have several racks worth of them, multiple W/G and precontrol and turbo control, plus back up actuators when running sequential twins, which to my mind, is the only way to assure ongoing reliabilty without costing the earth. For the solenoids at least, I was always looking for instant release (testing above operating pressure) when voltage was removed, not a slow bleed, then a pop.

Did find about 2 in every 3 second hand charge controls had perforated diaphragms and wouldn't maintain pressure and every used charge relief didn't meet mazda spec - not necessarily a problem. unless really bad.

I don't see it, hope you don't want to maintain the rubber coupler and plastic crossover for originality either...leave that for selling the thing!

It actually has an aftermarket silicone coupler for the crossover. I've debated on switching to the Efini Y pipe just for good measure as well.

The troubleshooting continues! Sorry for the long pause between updates, I've had IRL things to tackle.

So, since my last post, I've had the Efini Y pipe installed (all new gaskets on the secondary turbo side as well), a new CCV (with the new o ring), a new CRV, as well as the 3/4" 90 degree bend hose and the regular straight hoses replaced with silicone, as well as replacing the vacuum and pressure chambers. After all that, I am still getting that issue with the secondary boost. Is it possible the car is, for some reason, running on a tune with the PFC that has the secondary turbo set to work that way? I wouldn't think its the tune because it's not the exact same behavior every time, but it is very close. I'm basically out of ideas at this point.

Ok. You've really got unlucky with this!

One thing to check, I forgot I had to do on my own car, is the valve/ butterfly in the crossover pipe. The flap in there has gotten misaligned at some point and was hanging up. A little adjusting later and it was opening smoothly again.

If that butterfly is sticking, it would keep the boost from leaving the secondary turbo.

Just something easy to check.

Vince

Are you referencing the CCV? That one was tested and confirmed good.

Remember that exhaust flow goes up not only with boost pressure, but also with RPM. So it is possible that a clogged cat could cause loss of boost above 4500 even if there are no obvious issues below transition. And it would get worse the higher the RPM.

Also possible is that an intake restriction could cause a similar issue due to too much flow restriction to handle the higher RPM flow needs.

I did think that a clogged cat could be a possibility. However, I had one in my RX-8 and it literally would choke the engine and make it fall on its face. With my FD, it will slowly build boost but never reach 10PSI after the secondary transition, even in 1st or 2nd. So maybe it's a possibility that its providing enough of a restriction to slow spool?

How much it restricts flow would of course depend on how complete the blockage is. So it might not be completely blocked and give these symptoms - similar on intake restriction.

So at this point what is your boost pattern?

Have you tested the turbo control actuator itself to make sure it's holding and doesn't have a torn diaphragm?

May also need to do a one-by-one check of vacuum lines to make sure they are hooked up right.

Dale

Sounds pre-control/wastegate actuator system related. My initial guess is whatever (solenoid/PFC duty cycle/etc.) is supposed to restrict flow/pressure to the wastegate actuator in order to allow the actuator to remain closed and build boost, is not in fact restricting flow/pressure to said WG acuatator. You can CAREFULLY test this by disconnecting all hoses to wastegate actuator, and flooring it until you see 10psi post transition. (Obviously release once you see 10PSI since no wastegate actuator will mean no boost control and you will boost off your map)

This ensures your wastegate actuator is holding the wastegate closed properly. If the latter works, I'd start working up the control system chain, with the next stage being the wastegate actuator solenoid (stuck open? being told to open when not supposed to?)

It's also possible you just aren't running at 100%. What is the state of your plugs and wires?

Could also be the coil pack harness.

Do you know for 100% that the spark plug wires are hooked up right?

Have you tried swapping the electrical connectors for the WG control and pre-control that are bolted to the front of the UIM? That's super easy to do and see if it makes any difference.

Just read back through the thread, trying to remember what you've done and tried so far :).

The TCA you replaced, this is the actuator that's bolted to the exhaust manifold, correct? New one held pressure when you put a finger over the port?

Dale

I believe the plug wires are hooked up correctly. I took a before and after picture during the plug change, and the car runs perfect otherwise, though I will double back and check the wire routing.

I'll try swapping the WG and precontrol and see if that makes any difference. All of the solenoids are new, so it's possible they might have been switched, but it was behaving the same way before and after the solenoids were changed out, so maybe they were incorrect to begin with and incorrect when replaced in terms of those two being connected to the harness, though I think my mechanic would have noticed that, as hes familiar with FD's (typically I do my own work but for reasons I won't get into here I don't have that luxury at the moment.)

As for the TCA, yes indeed. Sourced it from tomsn16, verified working. I even changed the retainer clip for the rod for a brand new one. I do have his notes on the latest diag he performed that I'll post here in a second, that might shed some light on things.

Many thanks to everyone who has contributed their input and feedback on this post up to this point, it is very much appreciated!

Edit: my technician's notes -


https://cimg5.ibsrv.net/gimg/www.rx7...e4afe5452a.jpg

So I looked at the wastegate and precontrol, they are both connected correctly, white plug on the right. At this point I'm at a loss, I'm speculating it may be a clogged cat, but its weird how systematic it is, Exactly at 4500 is when the issue starts. I'd think if the cat was clogged, there would be some variance in that.

Have you tried removing all vacuum hoses from the WG actuator (essentially keeping the WG closed) and trying to hit 10PSI post transition/4500RPMs? This would isolate ALL control issues and would point to a clogged cat/bad actuator spring.

Like you mentioned, with how systematic it is -- my guess is something in the control system is preventing the WG from staying shut once the system switches to both turbos vs just primary. If you have a PFC -- datalogging could help.

I'll look into that, I'm worried about overboosting, though. But I imagine once I go over 4500, I control the throttle to maintain and keep it at 10PSI and prevent overboost? Sounds simple enough, I just don't want to be missing something because we all know the end result if this is done wrong, lol.

Edit: are those lines in question the two facing the front of the car?

Yes, if you're paying attention you'll be able to take your foot off the gas before 11-12 PSI. I've hit 14 PSI on BNR Stage III's with the stock PFC without fuel mods so take that for what it's worth. You don't necessarily need to floor it, you'll probably hit 10 PSI at 70% throttle but if you're flooring it and not even getting past 7 PSI even with the WG vacuum lines disconnected, then I'd start investigating the mechanical side of things (WG actuator, actuator pre-load, flapper door, clogged cat, misfires).

The lines depend on how your solenoids are setup but see picture for lines in stock configuration. Essentially you don't want ANY air going to the actuator for this test. In the stock configuration this means you need to remove the line from the primary compressor housing to the actuator.

https://cimg5.ibsrv.net/gimg/www.rx7...998c53e191.jpg


You theoretically could get away with just disconnecting the line to the solenoid (1), but a thorough test would have you disconnect both lines at the actuator (2 & 3).

Hope this helps -- I've spent years diagnosing various sequential issues.

So by both, you mean the lines at the wastegate and turbo precontrol?