Low secondary boost
 

Okay, I have done many searches and read almost every topic I could find on the subject of low boost from the secondary. I got my car about 5 months ago, 70k, Mazda reman. engine, stock, 5-speed. Everything worked fine until about a month and a half ago. I'm only getting about 6 psi from the secondary. My boost pattern is 10-8-(4~7).

Vacuum chamber is new, check valve is okay. I also checked the other check valve, and the other pressure tank next to the alternator. The I & J solenoids have been replaced (broke a vac nipple), and boost was the same before and after. They are hooked up correctly. I even swapped them and got the same boost pattern.

One of the troubleshooting pages said to unhook them completely and you should get a solid 7 psi. I got 7 psi from the primary, and about 4 from the secondary. I hooked them back up, and got the usual 10-8-6.

I checked the charge control actuator. With the engine on, the rod is pulled in, with it off, the rod is out. I also checked the crv. With vacuum applied, it was open. Without vacuum, the airbox end was able to hold plenty of vacuum from the vacuum pump, wich tells me the valve was closed, so it's working right. Correct me if I'm wrong.

I thought about maybe something with the wastegate, and turbo precontrollers. The original lines with the pills are still in place. If perhaps the hose was wider than the pill, this might cause a loss of boost. From what I read, though, this would affect the primary boost too. Can I just pull the pills out, put them in a new vac hose and put it back on?

I've pretty much eliminated any regular boost leaks (like the Y-pipe) because why would I still get 10 psi from the primary? What about the O-ring that connects the secondary outlet to the primary? If that leaked, it'd affect the primary boost too, right?

I've read about possibly a clogged pre-cat. I know a loss of boost in higher RPMs is associated. If it was my cat clogged, would there be any other symptoms? How could I check it? I don't want to have to buy a downpipe for nothing. Anyway, thanks in advance for the help.

Someone help please!

Why is it that no one replies to my thread, but I see stupid threads like "I think my car is the fastest" and the whole RX-7 community replies.

Every other post I have seen about someone having a boost problem, there's always several responses from the experts telling them what to check, what to do, and a suggestion on what might be messed up. Why don't I have a single response!!! HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

You know if you were having the problem, you'd want someone to help you.

It could either be your precat or main cat. Check the coupler on the cross over tube from your y pipe to your intercooler hose. Most likely a clogged cat.

I have got a similar problem. I also got som pretty bad boost spikes so I installed a manual BC on the wastegate, no I get 10 psi spikes and 7psi after spike, and my secondary boost is depends on the cars mood and is between 4psi to 10 psi. Usually its 7psi.
My mods are 3" downpipe and "poor mans cold air intake".

My theory is that the spikes and the low boost at high sec. turbo is realated.

Keep this in mind while I review your thread:

A downpipe is NEVER a waste of money. It is the best $300 yoy can spend to increase reliability.

You need at least 15" of vacuum from the vac chamber and 7.5 PSI pressure from the pressure chamber.

Have you tested them for these numbers yet? Do you know how?

These forces are required to force open the Turbo Control Actuator fully. It could only be opening partially/sluggishly.

Are you able to get full boost past 4500 rpm by letting off the gas and getting back on it?

I haven't checked for 15" and 7.5 psi, and I'm not sure how. All I did was check the vacuum tank and check valve for leaks with the vac pump.

No, even if I get off the gas, and back on, it still won't get more than 6 psi above 4500.

You're right about the downpipe, but I just gotta come up with some cash. Are there any other symptoms that only a clogged cat would give?

You need to do more than just seeing if the CCA and CRV are getting vacuum at idle. If you have a boost gauge then "T" into the vacuum lines going to the charge relief valve and the charge control actuator. If you don't have a boost gauge, by a cheap auto parts store gauge. Drive through the whole rev band and watch what happens in these hoses. There should be vacuum in both until 4,500 rpm at which time they will become pressurized. If that checks out fine, then move on to the turbo control actuator. I can never remember which side is vacuum and which side is pressure on that, so go to this site http://home.istar.ca/~dvandit/rx7stuff.shtml
It's extremely helpful and will help you better understand your problems. Also, if you want to check for a clogged cat or precat, you can pick up a little deal from most hardware stores that will let you check this: it has threads on one end, and a little ribbed nipple on the other(like for the hoses in high school chemistry class). You can put it in place of your O2 sensor and hook a boost gauge up to it. There shouldn't be more than like 4 psi of backpressure. Hope this helps.

Well, you asked for my help and here it is. Turbo control solenoid, vacuum side. P'cola pretty much hit it on the nail. If you have test his test, then the next logical test will be to remove the TC solenoid on the ACV under the UIM. This is easy to see, since it is the only solenoid that is different than the others on the rack. Pull it off, and test for continuity using a multimeter at room temp, then run it under hot water (without getting the terminals wet) and watch for the resistance to disaper. If it is bad, when heated it will fail. Normal ohms should be 33-37 ohms.

If you want to see the results of having a working solenoid on your car before buying a new one, you could do this: https://www.rx7club.com/forum/showth...threadid=54737

Okay, thanks guys. Looks like I've got a bit of testing to do tomorrow. I'll get back to you when I check the CRV, and CCV for vac/boost, and the cat converter check. I'm sure those will most likely check out, except maybe the precat. Then it will be on to the testing the TCA.

The Turbo Control solenoid probably is bad, but $60 isn't too bad compared to some of the other parts that could fuck up. I'll post back again tomorrow.

Thanks a lot!

Okay, I teed into the line going into the CRV and got no vacuum, and no boost. The silicone line I think was stretched and leaked around the tee fitting. I teed into the CCA and got the proper vacuum before 4500 and boost after that. So I then used the tee fitting to put this vac line on the CRV as well. It didn't help anything though. Is there a solenoid in the rack that controls the CRV? this could be bad in addition to the turbo control solenoid. Any ideas?

The CRV solenoid is item H in the Vacuum diagram.

I just located my slow sec. boost due to a hose popping off at the pressure chamber, now I got boost even at first gear!!!!:dunce:

Any progress?

White94, there is a solenoid that runs vacuum or pressure to the CRV. It is on the top of the rack and easily accessed. There are a few hoses to check along with the solenoid itself. Make sure all the hoses are connected and pay extra attention to where the hoses pass through the LIM. if there are a few hoses switched it will mess everything up. The CRV not getting any vacuum or boost will bleed off some boost when it gets high enough, which is bad. But at low boost it might not bleed much off, which will lead to compressor surge, also bad. Let us know what's up.

The solenoid for the CRV is item H in the vacuum/TCS diagram. It uses vacuum only as far as I know.

Okay, today the car was acting kinda weird at first. I would get maybe 1-2 psi, then it might slowly build up to 5-7. It wasn't too consistent either. One time the boost went up to about 5, and then fell to 0 by 6000 RPM.

Then, later tonight, it went back to the normal 10-8-5. It's not exactly consistent every time either. It could be like 10-7-4, etc.

I went to Birmingham over the weekend, and I was kinda thinking the pre-cat is getting clogged and restricted the boost. Maybe then it the crap got shaken or moved around, and I'm getting regular boost again. Any suggestions? I'm gonna do some more work tomorrow.

I didn't feel like reading all these post. Actually, I didn't even finish reading your post, lol, it's just way too long for me. I suggest getting rid of your cat and get yourself a downpipe. Your cat might be a little clogged. Also, the downpipe is an awesome reliability mod and it will increase your hp. Also, check your Y-Pipe and ic hoses for any cracks.

Do you always get 10 psi on the primary until the transition?

I used to ALWAYS get 10 psi on the primary. Like I said above, yesterday, it started acting kinda weird. It won't build any boost for awhile, then slowly it will start to make more boost, and eventually I get the usual 10 psi on the primary, then the drop at the transition. I think I need to put on a downpipe and see what happens. Any other ideas?

Get the downpipe. You need it anyway and it may solve your problem saving you a LOT of time, work and maybe money.

You should get the downpipe, but I doubt it will fix your problems. Start troubleshooting the control system.

Ok. as of today, it's doing the same shit. For the first 10-15 minutes, I get almost no psi. Then after awhile, it will make 10 psi on the primary, but boost builds slowly, and hits 10 psi closer to 3500 RPM. It feels like something is restricting the flow, that's why I think it could be the pre-cat. Any other ideas?

Do the poor man's no sequential and see if you can build 10 psi past 4500. If you can't get 10 PSI by 4500 then it must be your pre cat pooping out.

If you have the time, here is a set of instructions for the temporary non-sequential written by Mr. Farrag (Blackbelt Boost Master)
:
Time estimate: 30 mins to 1 hour, depending on how familiar you are with the car
Bottom of car

1. Jack up car and put on jackstands
2. Underneath the car you pull the clip off the pre-control and turbo control actuators.
3. Move the turbo control valve on the turbo to the front of the car, fasten with safety wire or or lodge it in place next to the actuator's rod (takes some manipulation) such that it stays open (again, when the valve on the turbo is pulled towards the front of the car, the TC valve is open)
4. Move the precontrol valve to the rear of the car and fasten with safety wire (optional...the TC is all that runs the car above 4500, PC is actually closed)

On top of car

1. Disconnect two vacuum lines going to charge control actuator and plug them off (a bolt or golf tee)
2. Safety wire the charge control flapper open (with no hoses connected, it is in the open position)
3. Tee charge relief into the blow off valve's control line - i.e. they are both connected to a nipple on the intake manifold
4. Disconnect the lines going down to turbo control (under pressure tank and crossover pipe, next to the WG/PC lines) and cap them off. Since you've used wire to hold the TC valve open, you don't need the pressure/vac for the actuators
5. Disconnect the precontrol actuator vent line that goes to the solenoid -- this is so that you constantly vent the solenoid and the actuator arm doesn't move. You could also leave the clip on the PC actuator, and cap off the precontrol actuator vent.

This will tell you what is going on with the car. I was having issues with my y-pipe gaskets leaking, and lack of non-sequential to produce full boost lead me to start examining for boost leaks. There is an alternate way to do this, by using vacuum hoses and routing them to the actuators/bypass the solenoids, but that won't help if you have malfunctioning components (pressure tank, vac tank, check-valves, etc).

Be aware that you may tap fuel cut with a stock ECU, as the car wasn't designed to run this way. Also, if you have a full exhaust/intake, you'll be dealing with boost creep, just like everyone else. Standard disclaimer applies!

Okay. I think I'll give it a try. I'll let y'all know what happens. Thanks for the help thus far.

This is my scenario. Do you have a good idea what might be causing this? Like you said, After I let of the throttle for a milli sec..(creating vacuum), then it kicks in to 10psi. -Thx

btardell, after the car has been turned off for a minute, pull the hose off of the vacuum chamber (not the one on top, the other one) and see if you can hear air going in. If you don't then you have a lot of hoses and solenoids to go through. The ones I can think of off the top of my head are the charge relief, charge control, and turbo control solenoids, that use the same vacuum system.

btardell,

You've likely got a vacuum leak somewhere between thevacuum tank and the turbo control actuator.

Popping the hoses off the vacuum and/or pressure tanks doesn't give a conclusive answer, but if you don't hear any air you know you have a problem. Conversly, you can still not have enough pressure/vacuum even if you hear air.

It takes both boost and pressure to make the turbo control actuator move quick enough (or at all) to deflect exhaust gasses to the second turbo which is required to develop full boost.

You would need at least 7.5-8 PSI created and stored in the pressure chamber (The black box on top of the motor) to push the TCA open.

You also need at least 15? of vacuum supporting the pressure side of the TCA to quickly open the TCA door to the secondary turbo for quick boost up.

By letting off the gas and flooring it again you have charged the system just enough to open that door using the vacuum system, and then sustain it by the increased boost produced by the combination of the two turbos.

To check (You will need a Mity Vac test pump.):
1. Check the Vacuum and Pressure chambers to make sure they are not leaking.
2. Then the check valves.
3. Then the hoses connecting to the switching solenoids as well as to the actuator its self.
4. Lastly, the actuator alone. It can leak too.

If you do not have the pump, there ways to use Vac/pressure test gauge and your boost gauge to osrt of check, but it is much more work and less accurate.

Get the mity vac.

You might want to start a thread of your own to avoid confusion.

Very helpful. Thanks

Okay, I did the nonsequential thing today. It doesn't seem to be working like it should. Like before, it won't build any boost for like 10-15 minutes after it's totally warmed up. And boost builds really slowly. I get almost 0 psi up to about 3000 or so and it starts to build slowly. By about 4500, I've got about 5 psi, then by 5500, or 6000, it peaks at 9 psi, then 8, maybe 7 by redline.

It seems like it could be something serious. It just started doing this shit about not building boost for awhile this week. When I was under the car, the precat heat sheild looks all darkish red, like it's just been burned up or something. Is it possible for the pre-cat to be restricting the boost in the lower RPMs, and not in the higher? I was thinking that in the lower range, the exhaust gas doesn't have much velocity, and the cat could be causing tremendous back pressure, not allowing the turbos to spool properlly and fast enough. And then maybe higher up the exhaust gas if forced through because the turbos are spinning so much faster they can push it (through the clogged mess?). Does this sound logical?

Have you checked your double throttle actuator yet?

Right...isn't there a one way check valve on that line too? You aren't supposed to be able to make full boost until the car is fully warmed up...it can cause dmage. That is what the double throttle control (DTC) prevents.

Check it out.

I've also have almost the same problem. Mine on the primary will go as high as 10-13 psi, then as the secondary comes in to play I usually get 8 psi. Now if i let off the gas slightly then put the pedal back to the floor it will climb up to 10. Although when drag racing you don't really have time to go through that process perfect so you'll get full boost with the secondary. I shouldn't have too right?...Also depending on how the rx-7 is feeling i will not even get 8psi with the secondary, sometimes 5-6psi... but it it rarely happens. I really would like to think that all it is is a clogged precat, and that the cure is a downpipe. I don't know. but time will tell i guess.

You might have a clogged precat and you NEED to replace it. Even if you do your symptoms make me wonder about your Turbo Control System.

5-6 psi after 4500rpms makes me think you are seeing little or no secondary boost. Does this happen even when you get 10 psi on he primary before the transition? You need at least 8psi from the primary or the secindary will not come online.

Yes..I'm pretty sure it still happens even when I reach 10 psi on the primary. Like I say it happens rarely and I'm not exactly sure. I'll go for a ride today and see whats really going on with the car. If a clogged precat is infact the problem and a downpipe is my answer, I've talked with peter farrell (PF Supercars) and he has advised me not to put a downpipe on the car without changing the cars computer. He says that since the car will boost higher it needs better fuel managment. Mind you this was just preformance talk, not talk about why i'm not boosting in full on the secondary turbo. Whats your opinion? Is there a way to get rid of the precat without getting a new downpipe? Or will the downpipe be ok and the extra boost gain not damage anything in the long-run?

Well Peter is the expert and not me. However, I think you'd be hard pressed to find many FD owners... if any who'd agree that you NEED a computer for a downpipe only. I wouldn't go as far as to say that a computer is a waste of money especially if you intend to mod further.

Do you have other mods that you neglected to mention?

Nope..the car is completely stock. I've spent about 1k in just doing alot of tuning up the car. You know plugs,wires,fuel filter trans fluid, diff fluid, new clutch, tires,boost guage,...etc. Just things to get it up to spec before any upgrades should be done. I just got the car in Jan. and it had 76000 miles. It now has 80000. I wish there were some guys where I live that owned one of these cars.. and if there was hopefully would have a clue on working on them. I could pay peter or someone else but that would just put a hole in my wallet and i wouldn't learn a thing. You know what i mean? I think I'll save a little $$ and get a downpipe and see what happens. There seems to be a lot of other FD owners that get them and don't really upgrade anything else right then. Where are you from technonovice? It would be nice if You and I could take a look at it... : ) Time will tell i guess.

I'm in Charleston, S.C. There are folks far smarter on this stuff than me. I wished they'd come around and post more. may of them stop posting help and I have learned why.

So many times I see good advice ignored, but the questions keep coming like they never heard the advice. It gets a little frustrating.

P'cola FD seems to very knowledgable and has a better grip than I do. I' still learning at my own slow pace. It isn't hard stuff, but you do have to know how it all works and then start thinking like a troubleshooter which requires analytical depth. I'm just an artist so I'm challenged from the start.

I'm going to try to find some time to think this tread over so we can get to the bottom of this. There are many FD's in VA. have you tried the regional section yet?

thanks for all the sequential turbo advice in this thread and in others Pcola and technonovice....:bigthumb: I've been paying attention to this thread since I've been having the same problems for quite some time now

11.5# on primary (PFC boost controlled)
7-8# @4500 rpm transition
bleeds down to 5 fairly quickly

basically a 10-7-5

primaries are working like a charm but secondary turbo control doesnt seem to be working like it should.

took out the main cat so my dp would vent exhaust into the atmosphere (and all over the underbelly of my car!)
Ran the car a couple times up and down the street (very loud) and as I suspected I still have the same boost problems. I highly doubt that White94's problems are an exhaust issue.

Tomorrow I'm going to start hacking away at the turbo control system and see if i can get anywhere with it.

I'd bet money you are getting NO turbo control as you already suspect.

Possible Culprits:
VACUUM CHAMBER: You need at least 15" of vacuum from the vac chamber.
To test the vacuum tank:
Tee into the vac tank with the vac gauge at either the vac tank itself, or the hose that goes to the solenoid rack. Same effect.
Run gauge into the cockpit.
Start car, go for a drive. You should see vacuum build up once the car starts and HOLD.
Then, the actual test is to find a hill and go up it in a higher gear where you won't gain much speed but will stay on boost for at least 10seconds.
Vacuum should remain high. If it drops, the first thing to check/replace is the check valve that feeds the vacuum system.

PRESSURE CHAMBER: 7.5 PSI pressure from the pressure chamber.

CHECK VALVE: Could be a bad valve or flipped backwards. The best way to test it is with a Mity Vac. The check valve between the vac tank the manifold can fail also. You should be able to blow thru the check valve from only direction. it is possible that the valve has been removed and replaced in the wrong direction. So do the vacuum tank test.

HOSES: Next would be hoses and looking underneath the plenum. I've heard of those brass lines clogging with crud to cause problems too.

ACTUATOR: The rod could be disconnected. Make sure that the clip has not disconnected from the Turbo Control (TC) actuator arm and the Turbo Control (TC) valve. I have heard and read a few cases of this. It could be this simple. The actuator could be damaged.

SOLENOIDS: There are 2 solenoids that connect to the Turbo Control (TC): one provides pressure on one side of the actuator diaphram and the other supplies vacuum on the opposite side.


to find out what is going on with your car is to tee your boost gauge into two locations:
1) The line that feeds the pressure tank, and tee into it before the check-valve: see boost build, drop at 3500rpms, build again and hold
2) The line behind the 1" charge relief 90 deg bend, which is the second turbo's activity: see nothing, boost builds at 3500 rpms, and holds. You should see numbers close to these below:

3rd gear - WOT

2000 RPM - 0PSI
3000 RPM - 0PSI
3500 RPM - 0PSI
4000 - 4500 RPM - Roll up to 8 PSI +-1PSI
4500 + RPM 10PSI

What is happening: Page F-84 in the manual

0-4000 RPM -
Precontrol controlled by ECU,
CRV off (Venting)
Charge Control Valve on (closed).
Turbo Control off

4000-4499 RPM -
Precontrol Optimized by ECU,
CRV off Charge Control Valve on (closed).
Turbo Control off

4500 RPM -
Precontrol fixed (5% open)
CRV on (closed) and Charge control valve off (open)
Turbo Control on

I'd bet you get O psi from your secondary, but its likely a TC problem rather than the turbo.

This is a great thread!

I am having problems with my Secondary boost after 4500 rpms. I get a strong 10-11 on the low rpms, the the boost guage just reads 0. I assume it does not go to the vacuum side because the primary turbo is still running. It is like I have only one turbo.

Sounds like I have my work cut out for me!!

I think if you have secondary boost issues this thread has almost everything you could cover. Be patient and read thru it all. It would be nice if one of our blackbelt, Jedi Knight, MVP boost masters would read thru and pick apart anything that is wrong and what is quite useful.

Great thread
 

P'cola FD

Thanks for the GREAT link. This is the best turbo troubleshooting page I've ever seen, BAR NONE.

My boost has been "having issues" and I have a lot more things to check after reading this page.

My primary turbo inlet hose has been cut down by the Air pump (after cold air intake install).

Do you think that could really cause a low boost I the primary like the site says? Hey WTF it's ONLY $100 to replace it. ;)

Thanks again

Same Problem now fixed
 

I had the same problem as described with an 11.5-6-slowly 10.5 and sometimes an 11.5-6-6 boost patterns.

After reading ALL of this very informative topic, I pulled my hi flo cat with 4,000 miles on it and low and behold, a whole lot of the internals dropped onto the garage floor. What a mess. The infeed side looked intact, white as can be. Could not see throught the discharge side. I took the catback off and shook a couple of small pieces out.

I put her all back together and now I have a consistent 11.5-7-10.5.

Not sure why the transition is so low now or why the secondary is not hitting the same as the primary, but maybe I just need to play with the Profec B a while.

Thank you all for the great info. I am heading to a track event at Putnam Park in Indiana on Thursday and this was cutting it a little close.

I did everything that has been said in this thread to check and stuff. I pretty much had secondary boost loss since i bought the car. You can see from my signature all the mods that i have. However i still get 10-8-8,7 psi always. I honestly don't know what could it be. I hope it's not the turbos, but it could be since that's the only thing i havent checked/replaced.

If there is trouble with secondary turbo boost coming online after the 4500 rpm switchover, look at:

Vacuum chamber line and check valve, vacuum chamber itself, charge relief valve and hoses, wastegate/precontrol solenoid pair, turbo control solenoid, turbo control actuator and vacuum lines running to/from the turbo control actuator.

A Mityvac will be useful in diagnosing the vacuum leak.

Re: Same Problem now fixed
 

Hard to believe your high flow cat could be toast after only 4000 miles? I've had mine for probably 50,000 miles? Was your secondary boost problem occurring after the 4500-rpm switchover point? If you lift off of the gas and create 20 inches Hg vacuum, and jump back on the gas, you can get the secondary turbo to come online. Track driving @ Putnam Park seems to suit the secondary turbos; we're feathering the throttle often. You might have trouble drag racing though...:)