FIX--sticking sequential turbos/ TCA /solenoid 'E'....Cheap, easy, fast and effective
10-27-17, 04:03 AM
#1
FIX--sticking sequential turbos/ TCA /solenoid 'E'....Cheap, easy, fast and effective
Background
Many drivers of stock-type sequentials may have experienced the following condition at one time or another: you make a blast, accelerating through the sequential transition point and onto the both turbos--so far everything is working fine. Then you lift for a gear change OR decelerate long enough for the rev's to drop below about 3000 rpm, and you mash it again only to find you have little or no boost--which only builds back up very slowly--while your frustration builds very quickly; if only this system worked every time! ....
The usual cause for the foregoing scenario is a sticky Turbo Control solenoid. Located in the rat's nest and designated as solenoid 'E', it is the pressure side turbo control solenoid and it works in tandem with the vacuum side solenoid (located up top on the ACV). Together, these solenoids are designed to apply pressure and vacuum to quickly and forcefully switch the large TCA (Turbo Control Actuator) located on the exhuast manifold below the twins. The position of this large actuator determines if exhaust is routed to only the primary turbo, or if both the primary and secondary turbos will receive their full exhaust for combined (parallel) operation.
If a turbo control solenoid should stick after both turbos are online, the TCA (turbo control actuator) will not release, and [only] a portion of the system will switch back to primary operation--while the exhaust will still be split between both turbos, remaining in secondary mode. The problem is obvious and this condition will result in little or no boost upon re-application of the throttle as well as a very long spool period to regain boost.
An easy fix
I developed the following solution around 2000 as a simple work around to the problematic 'E' solenoid; but for all intents and purposes, it is an effective permanent solution. There is no downside to this mod, and every sequential setup should have it as a fail-safe. It works based on the sequential's logic and It takes advantage of the fact that during valid secondary [turbo] operation, there will always be boost pressure present at the primary boost tap AND there will always be pressure applied to the TCA (via control solenoid E). During primary mode operation, however, there should be NO pressure applied to the TCA. Finally, when in parallel [secondary mode] operation and you let off the throttle, and if you let off the throttle enough, the system will vent boost pressure from the intake tract via the blowoff valves and reset the sequential controls to primary mode operation via the new check valve bleed circuit; under this condition there should be little or no pressure at the primary tap and NO residual pressure applied to the TCA. Given the foregoing conditions, it can be seen that the addition of a couple of 'Tees' and a single check valve can be used to form a pneumatic logic circuit that will bleed and release the pressure stored in the TCA; and hence, mitigate the problem of solenoid 'E' sticking. Sequential system function is thereby modified so that the TCA is still applied by energizing solenoid 'E', however; it is now discharged by both the new check valve bleed and solenoid 'E'; and therefore no longer dependent upon only solenoid 'E' to release. Since the TCA pressure is now discharged by the check valve, said solenoid will no longer be prone to stick; allowing it to immediately release, reset and be ready for the next sequential cycle. The advantage of using this method over a simple bleed port is that there is a much higher discharge flow rate and no constant leakage--a win-win. It maintains the full engagement speed of the TCA and allows for a very fast release of TCA upon deactivation.
Turbo control solenoid 'E' has proven to be especially temperamental in its operation and will often stick at random times. This seems to be more a result of the way Mazda chose to use these solenoids and not necessarily bad solenoids, or a bad design, per se. They were simply not spec'd correctly for the FD's application. My assertion is that these solenoids were likely designed for vacuum operation (and emissions control) and have been adopted for use with pressure--but were not specifically designed or adapted for it. I have observed that this particular solenoid does not operate reliably with pressure applied to its 'X' port--which is how it is used at position 'E' in the rat's nest. More specifically, the solenoid relies on a small amount of internal spring pressure to unseat its plunger once it is de-energized. It seems that the plunger is held closed by the residual pressure acting upon the plunger, since it is effectively a piston. This is likely the reason why those who have put pressure regulators on their pressure chamber have reported improvements in the operational of their sequential systems. And also could explain the improvement realized by those who switch over to the 'industrial' style MAC valve solenoids.
Please see the attached pics for the schematic and installation notes:
Many drivers of stock-type sequentials may have experienced the following condition at one time or another: you make a blast, accelerating through the sequential transition point and onto the both turbos--so far everything is working fine. Then you lift for a gear change OR decelerate long enough for the rev's to drop below about 3000 rpm, and you mash it again only to find you have little or no boost--which only builds back up very slowly--while your frustration builds very quickly; if only this system worked every time! ....
The usual cause for the foregoing scenario is a sticky Turbo Control solenoid. Located in the rat's nest and designated as solenoid 'E', it is the pressure side turbo control solenoid and it works in tandem with the vacuum side solenoid (located up top on the ACV). Together, these solenoids are designed to apply pressure and vacuum to quickly and forcefully switch the large TCA (Turbo Control Actuator) located on the exhuast manifold below the twins. The position of this large actuator determines if exhaust is routed to only the primary turbo, or if both the primary and secondary turbos will receive their full exhaust for combined (parallel) operation.
If a turbo control solenoid should stick after both turbos are online, the TCA (turbo control actuator) will not release, and [only] a portion of the system will switch back to primary operation--while the exhaust will still be split between both turbos, remaining in secondary mode. The problem is obvious and this condition will result in little or no boost upon re-application of the throttle as well as a very long spool period to regain boost.
An easy fix
I developed the following solution around 2000 as a simple work around to the problematic 'E' solenoid; but for all intents and purposes, it is an effective permanent solution. There is no downside to this mod, and every sequential setup should have it as a fail-safe. It works based on the sequential's logic and It takes advantage of the fact that during valid secondary [turbo] operation, there will always be boost pressure present at the primary boost tap AND there will always be pressure applied to the TCA (via control solenoid E). During primary mode operation, however, there should be NO pressure applied to the TCA. Finally, when in parallel [secondary mode] operation and you let off the throttle, and if you let off the throttle enough, the system will vent boost pressure from the intake tract via the blowoff valves and reset the sequential controls to primary mode operation via the new check valve bleed circuit; under this condition there should be little or no pressure at the primary tap and NO residual pressure applied to the TCA. Given the foregoing conditions, it can be seen that the addition of a couple of 'Tees' and a single check valve can be used to form a pneumatic logic circuit that will bleed and release the pressure stored in the TCA; and hence, mitigate the problem of solenoid 'E' sticking. Sequential system function is thereby modified so that the TCA is still applied by energizing solenoid 'E', however; it is now discharged by both the new check valve bleed and solenoid 'E'; and therefore no longer dependent upon only solenoid 'E' to release. Since the TCA pressure is now discharged by the check valve, said solenoid will no longer be prone to stick; allowing it to immediately release, reset and be ready for the next sequential cycle. The advantage of using this method over a simple bleed port is that there is a much higher discharge flow rate and no constant leakage--a win-win. It maintains the full engagement speed of the TCA and allows for a very fast release of TCA upon deactivation.
Turbo control solenoid 'E' has proven to be especially temperamental in its operation and will often stick at random times. This seems to be more a result of the way Mazda chose to use these solenoids and not necessarily bad solenoids, or a bad design, per se. They were simply not spec'd correctly for the FD's application. My assertion is that these solenoids were likely designed for vacuum operation (and emissions control) and have been adopted for use with pressure--but were not specifically designed or adapted for it. I have observed that this particular solenoid does not operate reliably with pressure applied to its 'X' port--which is how it is used at position 'E' in the rat's nest. More specifically, the solenoid relies on a small amount of internal spring pressure to unseat its plunger once it is de-energized. It seems that the plunger is held closed by the residual pressure acting upon the plunger, since it is effectively a piston. This is likely the reason why those who have put pressure regulators on their pressure chamber have reported improvements in the operational of their sequential systems. And also could explain the improvement realized by those who switch over to the 'industrial' style MAC valve solenoids.
Please see the attached pics for the schematic and installation notes:
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10-27-17, 03:58 PM
#2
Can you explain: does this solve a problem that exists with brand new OEM parts? I mean, new pressure chamber, all new sequential solenoids, all new check valves (OEM or Viton), replacement vacuum lines, even a replacement turbo control actuator? Or is this a way to not have to buy a new $50 turbo control pressure solenoid or a new pressure chamber?
Why do I need to bleed anything? There's a pressure chamber and a check valve and a solenoid. Are any of those components failed? Or has the turbo control actuator or exhaust manifold or turbos deteriorated to the point that a new solution is required if you don't want to replace literally everything?
Let me put it another way:
1. Is this a work around to buying new OEM parts? I mean there's nothing wrong with that, maybe the parts aren't available or they're too expensive, I'm just trying to understand alternatives.
2. Is this a solution for an existing problem that Mazda had with brand new cars? If I had a time machine and could install this on a new car in 1993 would it perform better?
Why do I need to bleed anything? There's a pressure chamber and a check valve and a solenoid. Are any of those components failed? Or has the turbo control actuator or exhaust manifold or turbos deteriorated to the point that a new solution is required if you don't want to replace literally everything?
Let me put it another way:
1. Is this a work around to buying new OEM parts? I mean there's nothing wrong with that, maybe the parts aren't available or they're too expensive, I'm just trying to understand alternatives.
2. Is this a solution for an existing problem that Mazda had with brand new cars? If I had a time machine and could install this on a new car in 1993 would it perform better?
10-28-17, 05:02 AM
#3
arghx, you raise some good points while looking at the problem from a different perspective. To answer your question, it is most accurate to say that it was intended as a solution to a problem that best fits your last description:
The answer is yes, it was created to fix an existing problem and it is likely that many cars would have performed better--meaning more consistently, reliably and as intended--at a time when these cars were new. It rather sucked to have an expensive, new car that performed inconsistently, and dramatically so. It was not conceived to replace worn or damaged components. Only to help the system function again as intended. Finally, this project was born out of frustration and aimed solely at the problematic 'E' solenoid that will occasionally hang and lock the system up (until it bleeds down). It was also thought to be a temporary solution until which time I could install a MAC solenoid in the 'E' position on the rack. ...And that MAC solenoid still sits quietly on my shelf today. Keep in mind that this whole deal dates back probably close to 20 years ago. It wasn't until years later that I got around to drawing and writing it up, taking pics, and so on. So most of this is me regurgitating much of what I did years ago--about 2006 being the most recent, although it's just as valid today. I finally decided to (re)post this information with some hope that it might be useful and help preserve some of our beloved FDs and also help out the current crop of owners and restorers.
My own frustration with this problem dates back to 1994, when after making numerous trips to two different dealers, it was never satisfactorily resolved. And that's when I set out to find a solution to the problem. (Keep in mind that I am an engineer after all.) So the dealers replaced most of the sequential solenoids a couple of times over, and the vacuum side turbo control--located on the ACV several more times with high hopes and assurances that the the problem would be solved. I want to point out that they recognized there was a problem, but ultimately could never fix it; suggesting it was a characteristic of the high-performance nature of the vehicle and that It was to be expected. I also know that there some pretty knowledgeable people that worked on it at the second dealership I sought out. After they changed everything out, and all was said and done, they were exhausted. Hell, I even received a new pair of turbos at 33K miles under warranty while they were chasing this problem--all to no avail. (As a side note, they could never find or fix the clunking pillow ***** in the rear suspension either, despite a valiant effort.)
I'm sure that much of the general frustration with the sequential system centers around this one problem which would never, ever had occurred had Mazda not decided to put pressure on the 'X' port of one of these solenoids. 'E' is the only one of the entire group so configured and the only one, after about 200,000 miles, that I've ever had an actual problem with. I have no recollection of problems with any of the others except for the nipples I've broke off during handling.
As I've mentioned before, I'm 100% certain that there is isn't enough internal return spring pressure designed into these solenoids to reliably unseat its plunger when typical boost pressure is applied (to the 'X' port). The problem doesn't seem to follow any logical order and doesn't care if the parts are brand new or well used--it is clear from the solenoids that I've personally encountered and tested that some are much better than others, and that their operation is, at best, inconsistent. Some test decent on the bench and will still hang when in the vehicle, so there are probably some thermal effects--go figure. Just to be clear, this is not a problem associated with any other parts or their respective condition, to the best of my knowledge. What I do know to be fact, is that once I installed this work-around, with all else being equal, I have never experienced the 'hanging' problem ever again. Period. Others that have tried this have had similar results. Had Mazda provided something like this on a TSB or as part of their recall program, I think there would have been many more happy FD customers and probably fewer parallel conversions.
I don't know if Mazda eventually fixed this in their later production 'unitized' black-box controls that were fitted to the JDM models. I have to believe that someone, somewhere within the factory knew about this problem, and chose to overlook it; similar in fashion to the infamous 3000rpm hesitation that was a result of a momentary fuel cut in the early ECU's that was never officially acknowledged. And like the hesitation problem, I'm sure the sticking sequentials afflicted some cars more than others, and for a lucky few, perhaps not at all. I do believe, however, this problem is, at least in part responsible for the FD's--as well as its sequential's--bad rap and reputation.
My own frustration with this problem dates back to 1994, when after making numerous trips to two different dealers, it was never satisfactorily resolved. And that's when I set out to find a solution to the problem. (Keep in mind that I am an engineer after all.) So the dealers replaced most of the sequential solenoids a couple of times over, and the vacuum side turbo control--located on the ACV several more times with high hopes and assurances that the the problem would be solved. I want to point out that they recognized there was a problem, but ultimately could never fix it; suggesting it was a characteristic of the high-performance nature of the vehicle and that It was to be expected. I also know that there some pretty knowledgeable people that worked on it at the second dealership I sought out. After they changed everything out, and all was said and done, they were exhausted. Hell, I even received a new pair of turbos at 33K miles under warranty while they were chasing this problem--all to no avail. (As a side note, they could never find or fix the clunking pillow ***** in the rear suspension either, despite a valiant effort.)
I'm sure that much of the general frustration with the sequential system centers around this one problem which would never, ever had occurred had Mazda not decided to put pressure on the 'X' port of one of these solenoids. 'E' is the only one of the entire group so configured and the only one, after about 200,000 miles, that I've ever had an actual problem with. I have no recollection of problems with any of the others except for the nipples I've broke off during handling.
As I've mentioned before, I'm 100% certain that there is isn't enough internal return spring pressure designed into these solenoids to reliably unseat its plunger when typical boost pressure is applied (to the 'X' port). The problem doesn't seem to follow any logical order and doesn't care if the parts are brand new or well used--it is clear from the solenoids that I've personally encountered and tested that some are much better than others, and that their operation is, at best, inconsistent. Some test decent on the bench and will still hang when in the vehicle, so there are probably some thermal effects--go figure. Just to be clear, this is not a problem associated with any other parts or their respective condition, to the best of my knowledge. What I do know to be fact, is that once I installed this work-around, with all else being equal, I have never experienced the 'hanging' problem ever again. Period. Others that have tried this have had similar results. Had Mazda provided something like this on a TSB or as part of their recall program, I think there would have been many more happy FD customers and probably fewer parallel conversions.
I don't know if Mazda eventually fixed this in their later production 'unitized' black-box controls that were fitted to the JDM models. I have to believe that someone, somewhere within the factory knew about this problem, and chose to overlook it; similar in fashion to the infamous 3000rpm hesitation that was a result of a momentary fuel cut in the early ECU's that was never officially acknowledged. And like the hesitation problem, I'm sure the sticking sequentials afflicted some cars more than others, and for a lucky few, perhaps not at all. I do believe, however, this problem is, at least in part responsible for the FD's--as well as its sequential's--bad rap and reputation.
Last edited by Speed of light; 10-29-17 at 10:33 PM.
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mikey13b (02-12-24)
10-29-17, 08:49 AM
#4
RX-7 Bad Ass
iTrader: (55)
This is a great idea and a great fix. I had this problem on my car many years ago, I swapped in another used solenoid and it was fine. But I can see this being a problem of randomness - some solenoids seem to handle it better than others.
Thanks for documenting this! For others doing this fix, I would recommend using brass instead of plastic T's, the plastic T's will fail over time with exposure to heat. I think some may be better than others but brass is just a good way to go. McMaster-Carr has a wide variety of T's for a very reasonable price.
I wonder if using a newer style Mazda solenoid might work better. The black box used the newer style as well as a lot of other Mazda vehicles. I have one I pulled from a junkyard that I need to do some testing with one of these days.
Dale
Thanks for documenting this! For others doing this fix, I would recommend using brass instead of plastic T's, the plastic T's will fail over time with exposure to heat. I think some may be better than others but brass is just a good way to go. McMaster-Carr has a wide variety of T's for a very reasonable price.
I wonder if using a newer style Mazda solenoid might work better. The black box used the newer style as well as a lot of other Mazda vehicles. I have one I pulled from a junkyard that I need to do some testing with one of these days.
Dale
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mikey13b (02-12-24)
10-29-17, 11:12 PM
#6
have a similar issue although mine is intermittent and is almost non existent when the car is fully warmed...
ive only noticed the difficulty in transition happening only during the early stages of the trip..
this also could potentially save me some frustration... not to mention additional work.. as im on the brink of going nonseq or perhaps single..
could be viewed as justification for some but not an easy decision for an ssm r2..
ive only noticed the difficulty in transition happening only during the early stages of the trip..
this also could potentially save me some frustration... not to mention additional work.. as im on the brink of going nonseq or perhaps single..
could be viewed as justification for some but not an easy decision for an ssm r2..
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11-13-17, 12:32 PM
#9
Would you say this fix is for the same "sticking solenoid" problem that people have running high boost on stock sequential twins and has also be remedied in the past by putting a pressure regulator on the solenoid rack to keep it around 10psi pressure?
12-11-19, 02:55 AM
#10
Bump from the dead!
I’m experiencing this problem, and will just so happen to have the UIM off in a couple weeks. I’m really torn between using this check valve mod (very nice!) or using the 3-way MAC 35A-AAA-DDBA-1BA with one port plugged or a similar 2-port solenoid in place of the OEM. (The OEM is normally closed?)
Anybody actually tried with an aftermarket solenoid?
I’m experiencing this problem, and will just so happen to have the UIM off in a couple weeks. I’m really torn between using this check valve mod (very nice!) or using the 3-way MAC 35A-AAA-DDBA-1BA with one port plugged or a similar 2-port solenoid in place of the OEM. (The OEM is normally closed?)
Anybody actually tried with an aftermarket solenoid?
12-11-19, 09:32 AM
#11
Wow! Thanks for the bump because I've never seen this thread. My RX7 has an intermittent primary boost issue and this sounds like a possible solution. I tested all my solenoids during my rebuild and an confident they all function properly.
What happens with mine is sometimes after a gear change or dip from secondary boost to primary rpm range the boost is slow building and peaks at about 5-7 psi. I also think the secondary transistion never happens but I hardly get the revs up that high when this happens. Usually if I let off the throttle for a fraction of a second (BOV relief) then get back on it the primary boost builds like normal up to 10+ psi and the secondary turbo switches on cue.
Will report back in 5 months when Wisconsin thaws out.
What happens with mine is sometimes after a gear change or dip from secondary boost to primary rpm range the boost is slow building and peaks at about 5-7 psi. I also think the secondary transistion never happens but I hardly get the revs up that high when this happens. Usually if I let off the throttle for a fraction of a second (BOV relief) then get back on it the primary boost builds like normal up to 10+ psi and the secondary turbo switches on cue.
Will report back in 5 months when Wisconsin thaws out.
12-11-19, 11:14 AM
#12
Didn't need the UIM off to make this fix. I am using this plumbing fix with a new stock solenoid.
tbk sticking solenoid sounds like your issue. Even if this isn't the cause of your current problem it's such an easy fix it's silly not to perform it. Something else to look at is the stock PFC settings have the secondary to primary switch over very low for my preference. I raised my 2-1 switch to 3800 rpm so I go back to primary operation sooner when letting off.
tbk sticking solenoid sounds like your issue. Even if this isn't the cause of your current problem it's such an easy fix it's silly not to perform it. Something else to look at is the stock PFC settings have the secondary to primary switch over very low for my preference. I raised my 2-1 switch to 3800 rpm so I go back to primary operation sooner when letting off.
12-12-19, 08:35 AM
#15
Use a Norgren R07-100-RNEA pneumatic regulator for the pressure tank (set it to 10 psi). Just take one hose off the pressure tank, add a extension, and run a line back to the pressure tank. I placed the regulator near the strut tower on the side opposite from the turbos to keep the heat down from reaching the regulator. This has worked flawlessly for the past 5 years. The stock solenoids never stick now.
Mike
Mike
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alexdimen (12-12-19)
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Nakd n Fearless (07-12-22)
03-30-20, 07:04 PM
#17
Full Member
2 questions regarding the diagram provided by the OP:
- At the bottome left it shows a restrictor in the line between the wastegates. Is this required or will my Adaptronic aftermarket ECU be able to control this without a need for the restrictor?
- At the top right it shows a gas filter between the MAP/Pressure Sensor and the UIM. Are fuel filters commonly used to replace the small filter that was installed in that area?
07-17-20, 04:39 AM
#18
Sorry to bump this one again...
My question for you guys is, doesn't adding a pressure regulator effectively create a boost leak?
Use a Norgren R07-100-RNEA pneumatic regulator for the pressure tank (set it to 10 psi). Just take one hose off the pressure tank, add a extension, and run a line back to the pressure tank. I placed the regulator near the strut tower on the side opposite from the turbos to keep the heat down from reaching the regulator. This has worked flawlessly for the past 5 years. The stock solenoids never stick now.
Mike
Mike
07-17-20, 08:26 AM
#19
RX-7 Bad Ass
iTrader: (55)
More or less. But it's VERY small and really you're regulating the pressure at the pressure tank. You aren't leaking enough that it will change performance.
Boost controllers kind of work the same way - they leak off pressure to the waste gate.
Dale
Boost controllers kind of work the same way - they leak off pressure to the waste gate.
Dale
07-17-20, 11:40 AM
#20
Mike