Weird Boost Issue

 
 
 
 
Old 08-24-04, 12:40 PM
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Weird Boost Issue

My apologies if this has been covered before. I've searched the forum and found about three posts describing my exact issue, but there were never any follow-ups explaining a fix.

Anyway, I've got a weird problem and wanted to see anyone has run into it before:

Details: PFC, Downpipe, Hi-Flow Cat, RB Dual Cat-Back, M2 Intake, new plugs, good wires, vac hose job, running 12 psi. I just installed the PFC and Steve Kan tuned it for me (great work!). I didn't have this problem with the M2 Stage III ECU I had before. I'm hoping its just that the PFC is more sensitive to something or there is a setting I've missed.

It does this in any gear, but for example, if I punch it in 2nd gear at 2500 rpm, I get full boost quickly, it transitions quickly to the secondary at around 4200 or so, and makes great power to redline... everything works great. However, if I let out of the throttle and coast back down to a lower rpm, say 4000, and punch it again, the boost builds very slowy and the exhaust note changes (sounds different, but hard to explain... different pitch). It will do this until the rpms drop below 2800 (either by coasting down in gear, or just putting the clutch in). I can coast all day (refreshing the vaccum supply), but I won't get quick boost back until the rpms drops below 2800...

Looking at the switch/relay readout on the commander, when I pass the transition point under heavy throttle, the CCN indicator goes out and the TCN comes on. It stays this way until the rpms drop below 2800, when it switches back and I can get quick boost again. Basically, I can get normal turbo operation once with WOT under a gear, and then I have to clutch in and let the rpms drop below 2800 before it will work right again. If I don't do that and then go WOT, it will take two or three thousand rpm to built back up to full boost.

I've tried replacing the turbo control solenoid (mounted on the ACV) and I also replaced the two solenoids mounted on the front of the upper intake (wastegate solenoid and pre-control) since they were easy to get to and those made no differences. I've also confirmed that all my checkvalves are good and my vacuum and pressure tanks are holding vac/press overnight.

Have you ever seen that behavior before. Any ideas?

From the exhaust sound change, I'm wondering if the wastegate or the other flapper door in the turbo manifold (prespool door) isn't functioning properly, but I can't figure out why it would work normally one time and then be screwed up until the rpms drop below 2800.

Is there any chance my PFC is bad? Everything else seems to work just great.

I'm going to take the upper intake off and check all the lines for kinks. I think I'll also replace the other turbo control solenoid (the one in the rack) while I'm in there.

Thanks for your time!
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Old 08-24-04, 02:04 PM
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Dang, Dave Disney! I haven't seen you around since the Big List heyday. Hope all is well!

Anyhow, the problem you're describing is VERY symptomatic of a bad check valve. I know you've checked them, but every time I've seen a problem where you lose boost getting back into it, it's been a check valve. The check valves aren't necessarily TOTALLY bad, just sub-par - like they'll only hold some vacuum, not full vacuum.

Have you tested them with a Mityvac?

Anyhow, glad to see you're still around! Hope the collective wisdom around here can shed some light for you .

Dale
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Old 08-24-04, 02:19 PM
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Hey Dave,
Sorry for not getting back to you on your issue. Been busy ever since I made it back to the shop. I was stuck in AL for 2 weeks waiting on parts for my engine. anyways, The PFC has a very large window for the sequential setup. I think it goes from 3000rpm to 4080rpm for the forbidden zone. So basically, once it hits sequential, it'll stay at sequential until it gets to 4080rpm before it switches to parallel or once parallel, it'll need to get below 3000rpm before it switches back to sequential. You can change those parameters with the datalogit. However, some cars tend to get oscillation or boost spike when closing the window too much or compressor surge when delaying too late. I left those settings to the factory Apexi PFC setting since not many people ever asked about the switching functions.

it's been awhile since I actually messes with or driving a car with the sequential setup using PFC so I could be wrong with what I said above but I'm pretty sure that is what it was.

also another thing that most people notice is that it takes more throttle on the PFC to get the car going whereas the stock ECU is much more sensitive to the throttle response. I personally think that it is more friendly to drive a car without any peaky throttle response



Originally Posted by autoxer
My apologies if this has been covered before. I've searched the forum and found about three posts describing my exact issue, but there were never any follow-ups explaining a fix.

Anyway, I've got a weird problem and wanted to see anyone has run into it before:

Details: PFC, Downpipe, Hi-Flow Cat, RB Dual Cat-Back, M2 Intake, new plugs, good wires, vac hose job, running 12 psi. I just installed the PFC and Steve Kan tuned it for me (great work!). I didn't have this problem with the M2 Stage III ECU I had before. I'm hoping its just that the PFC is more sensitive to something or there is a setting I've missed.

It does this in any gear, but for example, if I punch it in 2nd gear at 2500 rpm, I get full boost quickly, it transitions quickly to the secondary at around 4200 or so, and makes great power to redline... everything works great. However, if I let out of the throttle and coast back down to a lower rpm, say 4000, and punch it again, the boost builds very slowy and the exhaust note changes (sounds different, but hard to explain... different pitch). It will do this until the rpms drop below 2800 (either by coasting down in gear, or just putting the clutch in). I can coast all day (refreshing the vaccum supply), but I won't get quick boost back until the rpms drops below 2800...

Looking at the switch/relay readout on the commander, when I pass the transition point under heavy throttle, the CCN indicator goes out and the TCN comes on. It stays this way until the rpms drop below 2800, when it switches back and I can get quick boost again. Basically, I can get normal turbo operation once with WOT under a gear, and then I have to clutch in and let the rpms drop below 2800 before it will work right again. If I don't do that and then go WOT, it will take two or three thousand rpm to built back up to full boost.

I've tried replacing the turbo control solenoid (mounted on the ACV) and I also replaced the two solenoids mounted on the front of the upper intake (wastegate solenoid and pre-control) since they were easy to get to and those made no differences. I've also confirmed that all my checkvalves are good and my vacuum and pressure tanks are holding vac/press overnight.

Have you ever seen that behavior before. Any ideas?

From the exhaust sound change, I'm wondering if the wastegate or the other flapper door in the turbo manifold (prespool door) isn't functioning properly, but I can't figure out why it would work normally one time and then be screwed up until the rpms drop below 2800.

Is there any chance my PFC is bad? Everything else seems to work just great.

I'm going to take the upper intake off and check all the lines for kinks. I think I'll also replace the other turbo control solenoid (the one in the rack) while I'm in there.

Thanks for your time!
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Old 08-24-04, 02:52 PM
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Hey Dale, good to hear from ya! Its always good to run into someone from the old "Big List". Does it even still exist?

Thanks for the input guys. I didn't have my mityvac on me when I checked the checkvalves. I'll get it out and give them a good workout.

Steve, thanks for the info on the PFC sequential operation. Don't worry about the slow response, I heard you were a little busy with the 3-rotor

I may play with those settings a little if I don't find a checkvalve, pinched hose, etc. Tyler and Dillow have the exact same settings for the transitions as I do, but their cars don't seem to behave like I described above. Hopefully I just have a bad checkvalve or a lazy solenoid.

Thanks for the info guys (keep it coming)... I'll post back when I figure it out.
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Old 08-24-04, 03:12 PM
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Dave,

It's great to see your name here one the forum. Here's a thread that discussed a problem that seems to be similar (if not the same) as yours:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/what-you-using-address-delayed-pfc-boost-270920/

Hopefully it will provide some insight for you. Good luck!
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Old 08-24-04, 06:33 PM
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Yep, they're describing exactly the same problem I'm having. If I don't find a bad hose or checkvalve, I'm going to put a web cam in the engine compartment and see exactly what those actuators are doing and when they're doing it. I can hear a change in the exhaust note when its misbehaving, which makes me think the wastegate, turbo control, or pre-control doors isn't shutting when it should.
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Old 08-24-04, 06:34 PM
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Oh, I forgot to say thanks for the thread link! Thanks!
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Old 10-04-04, 07:51 AM
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Thought I'd make an update... I think I'm closing in on it.

I took the upper intake off and decided to do the block-off plates while I was in there. I kept the air control valve, since I still have a cat. But I eliminated the AWS, Double Throttle, and EGR. This let me take two solenoids out of the rack and simplify things a little.

I tested the turbo control actuator (big one on the bottom of the engine that uses pressure and vacuum). It worked fine. Then I checked the turbo control solenoid in the rack (3rd from the front). This one runs the pressure side of the TC actuator. It was sticking and acting weird. Sometimes it would stick open, sometimes closed. I thought I had it. Swapped in a good spare, put the car back together and went for a test drive.

It was a little worse than before

Now I get proper operation once and then pretty much no boost below 4500 after that. Letting the RPM drop below 3k doesn't reset it anymore. It'll make a pound or two under 4500 and then at the transition point, whap, full boost and power to redline. A couple of times while I was at wide open throttle at about 3k or so, it made 2 psi for a couple of seconds and then jumped right up to full boost, so I'm convinced that something is sticking (solenoid or actuator) and then popping free.

Also, there is a definite change in the exhaust note when the car is trying to make boost on the primary turbo (under 4500 rpm).

So, I started looking around and testing everything. I put vacuum on the A chamber of the charge control actuator (moves the valve in the Y-Pipe). It was slow to close when I removed the vacuum.... sometimes it would not close at all for about 30 seconds and sometime it would close halfway and after a little while it would close the rest of the way. Ah ha, I thought, thats it.

I removed the y-pipe and took the CCA apart. The actuator itself was fine, but the valve was gummed up a little and was causing it to be sticky. I cleaned and oiled everything and it worked smoothly. I put everything back together and went for another test drive. No change.

At this point, I've replaced both Turbo Control solenoids, the wastegate solenoid and the turbo pre-control solenoid. I checked again to make sure my vacuum and pressure tanks were holding pressure (they'll both hold overnight) and I've tested all the check valves multiple times with a mity-vac.

I've tested the operation of the CCA and done the key-on, key-off test and it passed. The only turbo-related solenoid I haven't replaced is the CCA solenoid. So I'm going to dig in and swap it out. I'm also going to check/re-test the solenoids that I've replaced so far, just to make sure I didn't get a bad replacement.

I'm convinced that something is sticking. If a new CCA solenoid doesn't fix it. I'm going to put my bullet-cam in the engine compartment and video the CCA, wastegate, pre-control, and turbo-control actuators and compare them to a healthy car. From the sound the exhaust makes I figure one of those is the problem. Also, my pre-control and wastegate actuators are pretty new (new turbos from Mazda a couple of years ago), so I haven't checked those yet, but they're next on my list.

Any thoughts?
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Old 10-04-04, 08:02 AM
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Have you popped off the pre-control, wastegate, and turbo control actuator arms to test the motion of the flapper doors?

IIRC the turbo pre-control does most of the primary boost control until 4500rpm, and if that's misbehaving it would cause lost boost. Of course, once they both come online, the pre-control door is not a factor. That sounds consistent with your latest symptoms. I don't think a crack around the pre-control would be the issue since you get full primary boost on the first pull.

The webcam is a neat idea. But wrap it in al foil or something - unless you want it nuked Just curious - would you be using a laptop to capture the video in synch with datalogit boost values? Cause that would be very nerdy-cool.

Dave
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Old 10-05-04, 12:00 PM
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Dave, as oulined in the thread in the regular 3rd gen forum, i've had this problem for YEARS, through a new set of RZ turbos, and replacing and checking everything you have... it has been to PFS, KDR, an RP and nobody has fixed it. I've actually found that running it with the pressure line to the TCA disconnected, that it actually works BETTER, but not perfect. It would only take you a couple minutes to jack it up, disconnect that line to the actuator (it's the one on the side), and see if yours does the same thing...

If you learn something, please let me know.



Originally Posted by autoxer
Thought I'd make an update... I think I'm closing in on it.

I took the upper intake off and decided to do the block-off plates while I was in there. I kept the air control valve, since I still have a cat. But I eliminated the AWS, Double Throttle, and EGR. This let me take two solenoids out of the rack and simplify things a little.

I tested the turbo control actuator (big one on the bottom of the engine that uses pressure and vacuum). It worked fine. Then I checked the turbo control solenoid in the rack (3rd from the front). This one runs the pressure side of the TC actuator. It was sticking and acting weird. Sometimes it would stick open, sometimes closed. I thought I had it. Swapped in a good spare, put the car back together and went for a test drive.

It was a little worse than before

Now I get proper operation once and then pretty much no boost below 4500 after that. Letting the RPM drop below 3k doesn't reset it anymore. It'll make a pound or two under 4500 and then at the transition point, whap, full boost and power to redline. A couple of times while I was at wide open throttle at about 3k or so, it made 2 psi for a couple of seconds and then jumped right up to full boost, so I'm convinced that something is sticking (solenoid or actuator) and then popping free.

Also, there is a definite change in the exhaust note when the car is trying to make boost on the primary turbo (under 4500 rpm).

So, I started looking around and testing everything. I put vacuum on the A chamber of the charge control actuator (moves the valve in the Y-Pipe). It was slow to close when I removed the vacuum.... sometimes it would not close at all for about 30 seconds and sometime it would close halfway and after a little while it would close the rest of the way. Ah ha, I thought, thats it.

I removed the y-pipe and took the CCA apart. The actuator itself was fine, but the valve was gummed up a little and was causing it to be sticky. I cleaned and oiled everything and it worked smoothly. I put everything back together and went for another test drive. No change.

At this point, I've replaced both Turbo Control solenoids, the wastegate solenoid and the turbo pre-control solenoid. I checked again to make sure my vacuum and pressure tanks were holding pressure (they'll both hold overnight) and I've tested all the check valves multiple times with a mity-vac.

I've tested the operation of the CCA and done the key-on, key-off test and it passed. The only turbo-related solenoid I haven't replaced is the CCA solenoid. So I'm going to dig in and swap it out. I'm also going to check/re-test the solenoids that I've replaced so far, just to make sure I didn't get a bad replacement.

I'm convinced that something is sticking. If a new CCA solenoid doesn't fix it. I'm going to put my bullet-cam in the engine compartment and video the CCA, wastegate, pre-control, and turbo-control actuators and compare them to a healthy car. From the sound the exhaust makes I figure one of those is the problem. Also, my pre-control and wastegate actuators are pretty new (new turbos from Mazda a couple of years ago), so I haven't checked those yet, but they're next on my list.

Any thoughts?
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Old 10-05-04, 09:21 PM
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Ok, today I replaced the Charge Control Solenoid. While I was in there, I went ahead and checked (using the shop manual's procedure) every solenoid again. They're all working just fine. My car behaves the same if its cold, so I don't think any of the solenoids are heat soaking and causing problems.

I put voltage to the turbo control solenoid (vacuum side) and the TCA operated smoothly. Then I did the same to the pressure side turbo control solenoid and the TCA operated smoothly. Then I removed the lines from the turbo control solenoids and used the Mity-Vac to actuate the TCA many times. It never showed signs of sticking.

I did the same (mity-vac test) on the Turbo Pre-Control and Wastegate actuators. I actuated them about 10 times each and they always operated smoothly.

I pulled the pill lines on the turbos off to check them while I was in there. I forgot that my turbos (being new from Mazda a couple of years ago) have the restriction integrated into the turbo housings, so I don't have any pills at all. I thought one might have gotten rotated or blocked somehow.

I put it all back together and took it for a drive. The problem seems to be getting slightly worse. I still get one good pull and then NO boost below 4500 after that. Letting it drop below 3000 or putting the clutch in doesn't always help.... and I'm still getting a droning noise in the exhaust system when the car is making zero boost below 4500.

When its making no boost below 4500, If I go WOT and then step off the throttle, and repeat about three times, it will eventually "break free" and make full boost again, until I run it past the transition once and the whole process starts over.

I think I've pretty much eliminated any sort of mechanical problem, so I'm going to attack the electrical next. Oh, I still need to actually pull the actuators off the wategate, pre-control, and turbo control doors and check them for adjustment and check them for smooth movement.... but I don't expect to find anything since it will work right for one pull.

I didn't get to try the camera, that's next, but I'm going to have to make a custom mount for it under the car. If I can tell for sure which actuator is staying open, compared to a healthy car, I can concentrate on it and check the eletrical and re-check the mechanical.

Bleh.
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Old 10-06-04, 12:38 AM
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OK, I tried. I think the turbo control might be sticking open. Here is my reasoning:

At 2200 rpm, first time you are testing it:

Turbo control is closed
precontrol is closed
wastegate is closed
charge control is closed
charge relief is open

you hit the throttle a bunch.

the exhaust spins the primary turbo and you get positive pressure in the intake tract.

the engine reaches 3000 rpm

turbo control still closed
precontrol begins to open, directing a bit of exhaust to the secondary turbo which begins to spin
wastegate is still closed
charge control is still closed
charge relief is still open

the engine sweeps through 4000 rpm

Turbo control still closed
precontrol opening further, secondary turbo coming up to speed
wastegate is still closed
charge control is still closed
charge relief is still open

the engine reaches 4500 rpm

Turbo control opens quick, feeding more exhaust from the rear rotor to the secondary turbo, giving it more energy than is only otherwise provided by the precontrol circuit. This also allows some of the energy from the front rotor to reach the secondary via the balance connection in the manifold
precontrol all the way open
wastegate is closed
charge control opens to allow secondary and primary turbo outlets to be combined IFF there is 8 psi (or more) on the primary side of the control actuator
charge relief closes to shut off pressure bleed to intake

the engine passes 5000 rpm (quickly, if in first!)

Turbo control fully open feeding exhaust from front and rear rotors to secondary turbo
precontrol fully open
wastegate begins to open, bleeding off exhaust pressure from the primary turbo side (front rotor), though there is a balance connection, so some of the exhaust pressure from the rear rotor likely gets bled off as well
charge control open
charge relief closed

drop the throttle, big vacuum signal

blow off valve opens to relieve positive pressure in front of intercooler, thus reducing turbo overspin into a vacuum

Turbo control closes
precontrol closes
wastegate closes
charge control closes
charge relief opens

If the Turbo control stuck closed always, only the precontrol would drive the secondary turbo, so low boost in secondary while primary works fine

If the turbo control stuck open, but the precontrol was closed, the wastegate was closed, the charge control was closed, and the charge relief was open, the exhaust that would drive the primary would mostly pass through the crossover in the manifold, drive the secondary turbo which would then vent to the intake box, and spin the primary only as much as the secondary became an impediment to exhaust flow, which would not be much, as the secondary is free to spin its gas away into the intake with no resistance. If the turbo control was stuck open until the engine passes down through the rpm range to below the 3000 mark, this would explain the symptoms, yes?

Further, if the turbo control was stuck open, and you gave it big throttle at say 5000 rpm after letting off a bit, you would still be in the situation to allow the system to make pressure. Once you drop below the 4500 mark, the charge relief opens and the charge control closes, blowing all the exhaust resistance to hell by spinning the secondary turbo to the intake box.

And if you hit the turbo control with repeated vacuum signals (WOT and off, WOT and off, WOT and off), you might unstick the actuator. It opens fine. but does it shut fine?

Does this make sense to anybody? I THINK this is how this silly sytem works...
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Old 10-06-04, 07:32 AM
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Dave, I've started to think "harness" as well. The only other explanation i can find is that we are looking in the wrong place... Does the "charge control solonoid" suggestion from Spurvo make any sense to you? ... I'd have to really re-styudy the opperation.


Originally Posted by autoxer
Ok, today I replaced the Charge Control Solenoid. While I was in there, I went ahead and checked (using the shop manual's procedure) every solenoid again. They're all working just fine. My car behaves the same if its cold, so I don't think any of the solenoids are heat soaking and causing problems.

I put voltage to the turbo control solenoid (vacuum side) and the TCA operated smoothly. Then I did the same to the pressure side turbo control solenoid and the TCA operated smoothly. Then I removed the lines from the turbo control solenoids and used the Mity-Vac to actuate the TCA many times. It never showed signs of sticking.

I did the same (mity-vac test) on the Turbo Pre-Control and Wastegate actuators. I actuated them about 10 times each and they always operated smoothly.

I pulled the pill lines on the turbos off to check them while I was in there. I forgot that my turbos (being new from Mazda a couple of years ago) have the restriction integrated into the turbo housings, so I don't have any pills at all. I thought one might have gotten rotated or blocked somehow.

I put it all back together and took it for a drive. The problem seems to be getting slightly worse. I still get one good pull and then NO boost below 4500 after that. Letting it drop below 3000 or putting the clutch in doesn't always help.... and I'm still getting a droning noise in the exhaust system when the car is making zero boost below 4500.

When its making no boost below 4500, If I go WOT and then step off the throttle, and repeat about three times, it will eventually "break free" and make full boost again, until I run it past the transition once and the whole process starts over.

I think I've pretty much eliminated any sort of mechanical problem, so I'm going to attack the electrical next. Oh, I still need to actually pull the actuators off the wategate, pre-control, and turbo control doors and check them for adjustment and check them for smooth movement.... but I don't expect to find anything since it will work right for one pull.

I didn't get to try the camera, that's next, but I'm going to have to make a custom mount for it under the car. If I can tell for sure which actuator is staying open, compared to a healthy car, I can concentrate on it and check the eletrical and re-check the mechanical.

Bleh.
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Old 10-06-04, 10:15 AM
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Spurvo, I think you have the turbo control operation figured out properly. At least that's also the way I understand it to work... but you gave a great, descriptive sequence to follow.

I agree that a stuck turbo control would cause the problem. I think a stuck (open) pre-control door would also cause the same issue, letting most of the exhaust gas go through the secondary turbo instead of the primary. Do you agree? I'm not sure, physically, where the turbo control flapper is in the exhaust system, so I don't know if having it shut and the pre-control open would rob the primary of exhaust flow.

My next step is to verify that either the turbo control or pre-control is open when it should not be... either with a video camera or just by tee-ing into the lines and watching the pressures.

However, I've checked and re-checked the operation of the solenoids and actuators and they are fine, but I have two thoughts:

1) The solenoids provide pressure or vacuum to the actuators to open them. But, in order for the actuators to close, the pressure/vacuum in the line has to be able to escape. What if the escape path for the vacuum/pressure is blocked, so even when the solenoid closes, the pressure in the lines cannot bleed off and close the actuator?

2) All of the solenoids are provided with 12 volts any time the ingition switch is turned on. The ECU opens the solenoids by grounding them. So, a worn ground wire could be shorting anywhere and closing the solenoid.... since it isn't on the 12v side, there's no fuse to blow or any other indication that anything is wrong.

If I can isolate which actuator is mis-behaving, I'll attack both the mechanical and eletrical side of it and look for problems.

Ptrhahn, what do you mean about Spurvo's charge control solenoid suggestion? I didn't see that he said anything about the CC solenoid, just the general operating points of the actuator.

Thanks for all the input guys!
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Old 10-07-04, 11:03 AM
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The only thing I can think of that might be a little different with the operation is the CRV and CCA. I believe once secondary transition happens and they are in their respective operating parameters they stay in that state until the rpms get below around 2800. From what I've read the car stays in secondary operation until this point leading me to believe that those will not change. Please correct me if I am wrong.
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Old 10-07-04, 02:19 PM
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First time I've looked at this thread but it sounds to me like the turbos are not always switching properly from parallel back to sequential during decel. I think you are completely right with it being some sort of turbo control actuator or door problem. I wouldn't bother hunting anything else as I think you've covered it all.

The only thing I can think of would be to disconnect the TCA from its door. Then you could wire the door open, make certain the car performs consistently and then wire it closed while making certain the car behaves consistently. Of course the boost will not function correctly but if the results are consistently repetitive in their respective case I would say it's safe to insist the problem is either the door or its control system. If the results with the door wired open/closed don't stay consistently repetitive you know you're fighting something else.
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Old 10-07-04, 03:54 PM
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Originally Posted by DamonB
First time I've looked at this thread but it sounds to me like the turbos are not always switching properly from parallel back to sequential during decel. I think you are completely right with it being some sort of turbo control actuator or door problem. I wouldn't bother hunting anything else as I think you've covered it all.

The only thing I can think of would be to disconnect the TCA from its door. Then you could wire the door open, make certain the car performs consistently and then wire it closed while making certain the car behaves consistently. Of course the boost will not function correctly but if the results are consistently repetitive in their respective case I would say it's safe to insist the problem is either the door or its control system. If the results with the door wired open/closed don't stay consistently repetitive you know you're fighting something else.

I've replaced the TCA with a new one and when I did it the door appeared fine. But doesn't the TCA stay open all the time in a non-seq system? If so then even if it stays open I should be able to get my boost back. I have a feeling its something with the pre-control/wastegate solenoids or something with the pressure/vacuum there. I might have to T into those. And does anyone know why there is a vacuum point connected to that area? Is it to offset the pressure that the lines from the motor are generating? To me that area is the most confusing section of them all. I want to know how it works.

I was thinking that maybe its electrical but my problem is too consistant to be electrical I think so I am steering away from that.
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Old 10-08-04, 01:28 AM
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If I got it right, there isn't really a vacuum or pressure control on the wastegate, unlike the controls that actuate the turbo control, charge relief valve, charge control actuator, and of course other things as well such as secondary air source routing and control (air pump and related errata). Rather, the pressure from the turbo output is routed from the nipple on the side of the primary turbo outlet (just under the air pump), through the wastegate actuator, then through the soft line to the relevant hard line that goes up behind the air pump, then turns to a soft line that attaches to the wastegate control solenoid. If you block one end of the wastegate actuator and blow in the other, the actuator pulls the rod in, which would open the wastegate on our turbos (and most others, I think). The ECU keeps the solenoid closed during pressured operation from the primary through 4500 rpm, then statrs opening and closing in the "duty cycle" mode to begin to modulate the wastegate actuator. As it opens and closes, the wastegate actuator responds by opening the wastegate. There is a restriction in this whole line to regulate the amount of pressurized air that passes through the line, thereby controlling the wastegate's effect. In the original turbos (early 93's), this restriction was from a little drilled slug of metal in the line right after the nipple, the so called "pill". Later turbos have the restrictor cast into the source nipple, necessitating a bit of drilling the allow finer regulation of wastegate actuation (read boost control). If there is too much pressurized air that can go through, the wastegate actuator opens the wastegate too far for a given amount of duty cycle at the wastegate control solenoid, resulting in less exhaust flow through the turbines, and therefore less turbo pressure. Likewise, restricting the pressurized air flow through this circuit (nipple to WG actuator, through hard line to solenoid, out of solenoid to vented air I believe) increases your boost by reducing the amount the WG opens for a given duty cycle.

The "Prespool" is really simply another wastegate, only rather than route the exhaust around the turbine to the regular exhaust (i.e. less exhaust to drive the turbo, so less pressure), the prespool routes its exhaust to the secondary turbo to begin spinning it . The principle of duty cycle regulation through restricted air flow from pressure source (litterally right next to the wastegate source) through the prespool actuator, through the hard line to the prespool solenoid, then to open air, is the same for both circuits. A pill or inline restrictor is also used.

I don't know if anyone put this site in here yet, but if you go to http://www.autosportracetech.com/RX-7/rx7stuff.htm you can find all sorts of neat stuff on turbo activities, including a really helpful cutaway diagram that shows the exhaust and intake paths.

I don't know if a stuck open prespool actuator would cause this in that it can be open and you still get primary boost (this is the case during transition at 4500 rpm, where you typically oinly drop to 8 psi from 10psi in the stock system), whereas the case described herein has zero boost until something "resets" below the point where the secondary system is activated at all. Not saying it isn't the problem, just that the deeper exhasut tone described indicates to me LARGE amounts of exhaust going where it shouldn't oughta..

That other post took me a day or so to figure out and write it all out to myself. I need to go through and play the mind game of "what if" for all the other possible scenarios to think if there is another route this could manifest. These turbos are actually part of why I bought the car. Secretly, I knida admire the engineers for dreaming up such a vastly complicated system to try and provide seamless boost from sequential small turbos. Masochistic and all that..
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Old 10-08-04, 08:01 AM
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I am pretty sure it is vaccum from the air-inlet of the primary turbo that connects to the little cylinder that also has the pre-control, wastegate, and the 2 nipples from the block that I assume could have vaccuum or pressure. That's kind of what is confusing me. Why should a hose that should always have vaccum be connected to that little metal cylinder when its pressure that is required to operate those two actuators? Unless it somehow offsets the pressure created by the two other nipples. On the Robinette vaccum diagram its the dark blue sections I am referring to. I have an understanding of how the actuators work I am just dumbfounded on the vacuum/pressure system related to these two soleiods.

But I agree with you. This seqential system lets me go play in the garage, gives me some time away from the wife.
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Old 10-09-04, 12:07 AM
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Ok, I worked on it again today and figured out what the problem is. But I still haven't fixed it.

Started out by re-checking the check valves for the vacuum and pressure tanks. In addition to vacuum testing them, as I'd done before, I also applied pressure to them. One (the vacuum tank valve) could only withstand about 10 psi of pressure, so I replaced it with a new one that would take 20 psi.... but I didn't think that was the problem and turns out it wasn't.

I checked the vent lines for the wastegate and pre-control solenoids (the lower nipples on each) to make sure they weren't blocked and holding pressure. They were fine.

I also checked the vent filters (the little round filters that are attached to the solenoids) on both turbo control solenoids to make sure they weren't blocked. They checked out ok.

Then I checked the adjustment on the Pre-Control and Turbo Control actuator rods. Both were OK.

Now here is where it gets interesting.

I bought a $20 web cam from CompUSA. It is crappy quality, but it has a built in white LED light and is USB and capable of 30 frames per second. The light was a plus (in a dark engine compartment) and I didn't want to risk my expensive ChaseCam if I didn't have to.... turns out that was a good idea (read on).

I placed the camera where I could see the Charge Control actuator and went for a test drive. It behaved exactly as it should, actuating at 4500 and turning off at 3000. I did quite a few runs and it worked perfectly every time.

Next, I placed the camera where I could see the Turbo Control actuator. I did a WOT run in second gear and the TC actuated at 4500 (as it should). Then I coasted back down to about 2800... TC stayed open, 2500 rpm, still open, put the clutch in and stopped. About the time I stopped it finally shut. I did several test runs and it behaved inconsistently every time. Sometimes it would slowly open after dropping below 3000, sometimes it wouldn't open at all, sometimes it wouldn't open until I hit 3500 or 4000 on the way back up during another WOT run.

Then the camera melted I figured there was enough airflow down there to keep it from melting (guess I should have used that aluminum foil tip, Dgeesaman)

So the TC is the problem.

I hadn't checked the TC actuator while the car was hot ('cause I don't like being burned ). So I checked it right after a few WOT runs. The vacuum and pressure lines for the TC run right behind the air pump and are pretty easy to get to there. I hooked my mity-vac up there and applied vacuum or pressure to the TC actuator and it worked perfectly every time. I thought about going ahead and replacing the TC actuator with a spare, but thought I would run another test first.

So, then I tee'd a vac/pressure gauge into the vacuum side of the TC actuator and went for a drive. It worked perfectly. At 4500 I would get vacuum on the gauge and at 3000, poof, the vacuum gauge dropped to zero.

Went back home and moved the gauge over to the pressure side of the TC actuator. The pressure side of the TC line is showing the same weird behavior that the video camera revealed. The pressure never left the line at 3000. Sometimes it stayed pressurized (TC open) through several runs, causing zero boost below 4500. Sometimes it releases after a few seconds, etc.

So.... something is keeping the pressure from leaving the TC actuator.

It can't be wiring because: Both turbo control solenoids are wired together to a single output on the ECU. Recall that the ECU grounds the solenoids to activate them. If one solenoid connection had a frayed wire that was grounding intermittently, it would also activate the other solenoid, which isn't happening. It can't be an ECU problem for the same reason. The ECU only has one wire to ground for both TC solenoids, so if it was keeping the solenoids activated, I would have also seen a problem in the vacuum TC solenoid.

I can't think of anything the TC actuator could do that would keep pressure in the line. When the pressure TC solenoid shuts off, it basically switches the TC actuator (pressure side) from being connected to the pressure tank to being connected to a vent to atmosphere (thus dumping the pressure from the line and shutting the TC door).

So, that leaves me with two possibilities. A) My replacement TC solenoid (pressure side) is also bad or B) I have a restriction in the line between the TC actuator and the TC solenoid.

I've tested the pressure TC solenoid several times (and replaced it once), but not when its really good and hot. It could be failing when it gets warmed up.

But I'm betting on option B. I think there is gunk (or something) in one of the steel pipes that connects the TC solenoid to the actuator. That would also explain why so many people have had this problem and replacing everything (solenoids, actuators, etc.) doesn't fix it.

I'll find out tomorrow and let you guys know. I'm going to check the steel pipes and clean them, or just bypass them completely with a long piece of hose. I will probably also replace the pressure side TC solenoid with a 3rd spare that I have.

Also, I can post those videos I made if anyone wants to see them. They are really poor quality, but all I needed to see was the actuator arm move.

- Dave Disney
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Old 10-09-04, 01:02 PM
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Fixed

I fixed mine this morning. And do I feel stupid. Hopefully the rest of you have the same problem so I won't feel as bad. But I had the pressure/vacuum hoses switched for the TCA. I have no idea how I had secondary boost the first try and then it fail. But anyway now I get it all the time and boy is it nice. Feels amazing. hehe

The area between the rats nest and the metal pipes by the airpump is where they weren't connected right. I went out with one T-ed and saw pressure and it appeared to work correctly in the sense of when it applied pressure and when it released it. Then I got under the car and applied pressure to that same hose with my mityvac and the arm never moved. So I tried vacuum. Then it moved and then I knew I F'ed up.

So go double check that.
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Old 10-09-04, 01:29 PM
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I fixed mine too.

It was the pressure side Turbo Control solenoid. The one I replaced it with was also bad.

Both the original solenoid and the replacment still pass Mazda's check procedure (in the shop manual) with flying colors.

But here is what's happening. There is a spring in the solenoid that returns the valve back to its initial position when the power source is removed from the solenoid. Over time, the heat weakens that spring and the pressure in the line between the solenoid and the turbo control valve holds the solenoid open (the spring cannot overcome the pressure). So, the pressure can't escape and the turbo control actuator is held open when it should not be.

The solenoid I had in the car couldn't take more than about 9 psi without sticking. The original solenoid in the car couldn't take more than about 11 (I'm running 12.5). I tested several spares I had and finally found one that was happy even at 15 psi. I put it in the car and went for a test drive..... car now performs perfectly and life is good

I can post a detailed test procedure for the solenoid valve if anyone is interested. You basically need to put 12v and a ground to the solenoid, then put pressure (about 12 psi to start) on the nipple that would go to the actuator and then remove the 12v and see if the solenoid lets the pressure in the line vent. If it doesn't (or is very slow doing it), then you have a problem. Let me know if anyone wants a nice how-to with pics. You have to test it as it is used in the car, the blow through test the shop manual outlines will not work with this solenoid. A very bad solenoid can still pass that test.

Thanks for all the troubleshooting help guys. My advice, if you're having the problems described above would be to buy a NEW pressure side Turbo Control solenoid.

- Dave Disney
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Old 10-09-04, 01:35 PM
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Great troubleshooting skills! While I don't have this problem, I learned a lot just reading about how you guys trace these problems down.

I'd love to see the videos, and a how to with pics would be great!

Congrats on finding the issue!

BTW, assuming a Mazda tech could have found this issue, what do you think the charge would be?
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Old 10-09-04, 01:38 PM
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Glad yours is fixed. I have a feeling my hoses were correct at one point and then sometime when I was tring to fix things they got swapped. I had to replace my TCA since the pressure side wasn't working and I bet I got those hoses mixed up before that and never thought to check it again.

I still don't understand how I got secondary boost with the hoses mixed up though. Makes no sense.

Anyway, I certainly wouldn't mind a nice write up of that testing procedure since I am sure I will need to use it at some point.
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Old 10-09-04, 01:49 PM
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I'll post the videos and a solenoid check how-to in the next couple of days.

I worked on the car about 14 hours over about three different days. So, multiply that by their shop rate... probably seven or eight-hundred dollars by the time you factor in all the new parts they'd have put on the car trying to figure it out. I doubt they'd have ever figured it out though. Trying to even explain the problem to a regular shop mechanic would have been a nightmare.
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