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What are you using to address the delayed PFC boost?
I don't think i am alone on this matter.
I have a PFC and sometimes there is a lag, as if it thought it was non-sequential and then boost would kick in at a much higher RPM. My post on the boost controller more or less revolves around this thread. |
That's because the PFC stays non-sequential once you cross the transition until your revs drop back below 3000 rpm. I simply kick the clutch after merging on the freeway to get it back into sequential mode.
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interesting.....
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Mine does this too, but its not a PFC problem, it did it with the farrel computer too... and i know alot of people with PFCs that don't have the problem.
This is something else wrong in the car, and i've gotta tell you, i've had a few shops look at it and not be able to fix it... Originally posted by rynberg That's because the PFC stays non-sequential once you cross the transition until your revs drop back below 3000 rpm. I simply kick the clutch after merging on the freeway to get it back into sequential mode. |
its the way the car is designed. I dont know the technical term but it has to do with the sequential system and some valves opening/closing. The only "FIX" is goind non-sequential or single turbo.
You can easily test this, drive your car on the street in 2nd gear. take the car all the way to 5000 from stop. Then lay off the gas and coast for 1/2 second or so but keep the revs above 3000. Floor it again the car will be a dog. Then let the car drop to 3000 RPM and floor again, you will spool super fast. |
Originally posted by ptrhahn Mine does this too, but its not a PFC problem, it did it with the farrel computer too... and i know alot of people with PFCs that don't have the problem. This is something else wrong in the car, and i've gotta tell you, i've had a few shops look at it and not be able to fix it... The PFC is supposed to work that way, keeping the car in non-sequential once you've crossed transition. It makes the car a lot safer to drive on the track, that's for sure. The best part is with the PFC, you get all the benefits of non-sequential -- smooth reliable powerband -- on the track, and then have the low end of the sequential setup on the street. I think you may be thinking of a similar problem that people with slow boosting after shifting....I don't have that so I can't comment. |
When I had the stock ECU it never had that problem.
But since I had the PFC I didn't really dive it hard and my shift points are different. I'll change my driving style. Thanks for the tip Rynberg. |
check your vaccum actuator under the secondary intake pipe. Mine was sticky and I had this delayed response. However, I had a leaky vaccum check valve too so may be it was a combination of both.
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I don't think this is the way it's supposed to be with the PFC or any other aftermarket computer (like the farrel). It did not do it with the stock ECU... its definately supposed to go back... apparently theres even an RPM setting in the PFC (if you have a dataloggit) that specifies at what RPM its supposed to transition back.
It sounds like shit when you let off the gas and try to get back on... a farty sound and terrible boost response (because the flapper door hasn't come back). Its not consistent enough to be designed in (sometimes I actually have to let the car come back to idle to get it back, sometimes it comes back in a second) I would put my money on a vac. leak somewhere, or a sticky actuator. Originally posted by rynberg I don't think there's anything wrong with the car. The stock ecu did it too, although it didn't seem as obvious. The PFC is supposed to work that way, keeping the car in non-sequential once you've crossed transition. It makes the car a lot safer to drive on the track, that's for sure. The best part is with the PFC, you get all the benefits of non-sequential -- smooth reliable powerband -- on the track, and then have the low end of the sequential setup on the street. I think you may be thinking of a similar problem that people with slow boosting after shifting....I don't have that so I can't comment. |
I have had 2 sets of turbos and 2 engines and the stock ecu and the power FC, in all circumstances the same thing happened. My hoses have all been done professionaly. Still happens on my car. I will not comment on a "sticky valve" cause frankly, I dont know. But I can say its not a vaccuum leak or hose problem.
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During slow acceleration(no boost) to 3000-3500rpm, the precontrol is close, so no flow to secondary.
I think if you floor it at around 3500-4000rpm, there just not enough time for the secondary to spool up, and produce enough boost. so only the primary giving boost, but secondary is too late spooling up at transition, so your boost is low 5psi normally or less... then it goes back up. |
My vacuum hose should be fine since I had the full silicon hose swap.
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I posted a chart on my website listing the inputs and values that the pfc uses to control the switch-back point. I had the same problem with my old motor. After I put in the new motor, added an efini Y, and grounded the hell out of everything it went away.
http://www.carlisiworld.com/ccarlisi...3/interest.htm You can adjust the switch-back values using a datalogit. However, I'm told that the adjustment range is relatively narrow and certain values are limited with reference to other values. The next time I plug the datalogit into my car I'll play around with them and report back. |
Grounding is something i hadn't thought about... i'll bet mine isn't the greatest.
What exactly did you do and where? |
My stock ecu did it, my stock ecu with PFS PMC did it, my M2 stage 3 did it, even the PFC does it. 70K on the car. Rynberg's right, but I think it has to do with the vacuum and the solenoids, not just dropping below 3000 rpms. It's basically running in parallel at that point and that's why it feels slow.
Tim |
As Ccarlisi brought up, the datalogit allows you to change both the transition point and the point at which the turbos will drop back to sequential once going past transition. They are NOT independent controls. If you try to raise the sequential rpm, your transition point will increase. This is most likely due to the vacuum/boost control system as Tim brought up.
In the end, it just becomes another little quirk of driving the car. I love that it does it when on the track, just not so much on the street. |
I think this is all due to turbo inertia
having a sequential turbo get things worse but this happens also with a single turbo car. I noticed it also sometimes the car seem really much faster than other times and bbosting in a completely different way |
This may also be due to the fact that PC and TC are related to pressure and not only revs.
Being pressure different at same revs upon drive/loads conditions make them work in different ways, so sometimes the car feels slower, having not time to "feed" turbos with exhaust gases quickly enough, cause of , as I said, turbo inertia. This happens also with single turbo car, because WG is again actuated with a pressure signal. Hope I explained myself well enogh |
This is one of the reasons at times my Rx-8 is more fun on the street. With the Rx-7 if you Launch it and run it in WOT till redline and shift nothing compares to it, its aamzing. But try to keep it in the 6000 RPM power band and you run into these problems.
With my Rx-8 I can drive it at 3000 Like a granny and still pull very good, or I can keep it at 6000, 7000 or 8000 RPM all day long. I wish the FD could do that, oh well. |
when i first got my car it would do this that was almost 4 years ago though..... one of the many reason i went single turbo....
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This is nothing "inherant" in a twin turbo system.
The bottom line is, something is malfunctioning, and not returning the door inside the manifold to blow exhaust (almost) exclusively at the primary turbo when its supposed to, requiring you do do something "more" to trigger that action, like letting the car idle. I'd even think that its something vacuum or mechanical in origin, because given the sound of the motor, i'd say your ECU isn't delivering fuel and timing maps consistent with what the turbos are doing... in other words, if you TUNED for a non-sequential car, it wouldn't sound like that... the maps your getting weren't intended for the conditions, because those conditions weren't intended. Bottom line is, it's not "poor boost response" its poor or faulty system management... the door should be coming back, and its not... ergo, something isn't doing what its supposed to be doing. |
Its not a problem if the system was designed that way.
Design flaw to some, blatently useful to others. I mean comeon, its not exactly hard to keep the revs high enough so that you dont get the "dog" in lower RPMS. I mean jeeze, if anything you downshift people. If u can do it quick enough, its gonna stay in parallel the whole time, EXCEPT you'll be in a useful area of the power band. If your really wanting to move with anycar, why be outside of its powerband? I for one dont floor it in third gear till 7krpms, coast it to 3k and then floor it again from 3k, I'll downshift to second. Makes no sense to start outside the powerband especially in a higher slower revving gear. Whats the big deal? Its not a problem if you drive how your supposed to be driving. |
You're not getting it.
This isn't a technique problem, and it was not designed in. The system is a sequential system. The "door" opens at around 4500 (or whatever), and then should return to sequential mode when you drop below a certain RPM. My car (and many other peoples cars) did or do this properly, the way they are supposed to. Mine doesn't anymore. When it happens, it is not "usefull" in any way, either on track or on the street. Let me repeat this: It SHOULD NOT do it, and there's ZERO positive effect to it. PERIOD. Its not a matter of "keeping the revs up", because its triggered (or not triggered) by backing out of the throttle. Let me give you an example: I decide to accelerate hard on the street (maybe i'm racing somebody). I pass the transition point and maybe get to 6k rpm, then because of traffic, a corner or what not i have to get out of the throttle... If i try to get back into the throttle a moment later (push the accelerator back down), I have no boost, and there's a distinct fart resonance to the exhaust sound, and it won't rev freely. Blipping the throttle and choosing a lower gear doesn't help. At this point, all the rpm in the world doesn't help. I have to press the clutch, and let the RPMs drop to idle, then i can reengage the gear, and get boost back. Magically, i can now build boost and the car sounds right even though i'm not travelling at a significantly different speed, nor are my RPMs, or gear selection any different than they were before i dipped the clutch a moment ago. ... and this is because dipping the clutch triggered the door to come back, and now its in the position it SHOULD HAVE BEEN IN at this RPM without me having to dip the clutch. I defy anyone to find me a Mazda engineer who worked on this cars development that will tell me that Mazda INTENDED me to have to do this. There's no good purpose for it, it does not make the car "more drivable" on the track or anyplace else... it behaves like its in Limp mode for gods sake. Originally posted by Rx-7$4$me Its not a problem if the system was designed that way. Design flaw to some, blatently useful to others. I mean comeon, its not exactly hard to keep the revs high enough so that you dont get the "dog" in lower RPMS. I mean jeeze, if anything you downshift people. If u can do it quick enough, its gonna stay in parallel the whole time, EXCEPT you'll be in a useful area of the power band. If your really wanting to move with anycar, why be outside of its powerband? I for one dont floor it in third gear till 7krpms, coast it to 3k and then floor it again from 3k, I'll downshift to second. Makes no sense to start outside the powerband especially in a higher slower revving gear. Whats the big deal? Its not a problem if you drive how your supposed to be driving. |
Originally posted by ptrhahn Let me give you an example: I decide to accelerate hard on the street (maybe i'm racing somebody). I pass the transition point and maybe get to 6k rpm, then because of traffic, a corner or what not i have to get out of the throttle... If i try to get back into the throttle a moment later (push the accelerator back down), I have no boost, and there's a distinct fart resonance to the exhaust sound, and it won't rev freely. Blipping the throttle and choosing a lower gear doesn't help. At this point, all the rpm in the world doesn't help. I have to press the clutch, and let the RPMs drop to idle, then i can reengage the gear, and get boost back. Magically, i can now build boost and the car sounds right even though i'm not travelling at a significantly different speed, nor are my RPMs, or gear selection any different than they were before i dipped the clutch a moment ago. ... and this is because dipping the clutch triggered the door to come back, and now its in the position it SHOULD HAVE BEEN IN at this RPM without me having to dip the clutch. |
sounds like a sticky actuator issue.
j |
You are correct, rynberg, mine is a different problem than what you're talking about... basically, i'm NOT getting that return at 3k (or whatever) like i'm supposed to. And it certainly shouldn't SOUND like it does.
... but i was reacting to someone's suggestion that this is a problem with ME. I dunno about BATMANs issue, maybe my longer description will help him sort it out. Originally posted by rynberg Ptrhahn: That is NOT the situation I am describing at ALL, though it may be Batman's problem. The phenomenon I am describing is not a mechanical problem but a design of the system. Once you cross the transition with the PFC, it will stay in non-sequential until you drop below 3k rpm. That is how it is SUPPOSED to function. I never have to return to idle or any other nonsense in order to get boost. My only point was that you have to drop the rpms below 3k to go back to sequential. This is really only noticeable in 5th gear and not normal driving -- in fact the only time I really notice it is merging onto the highway at 100 mph or so in 4th and then dropping it into 5th -- the car will still be in non-sequential in 5th gear, which is slow as shit as any non-seq people will verify. |
The "Problem" with my car is exactly as Rynberg described.
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woah now, I mis-interperated as well. I thought it was just the system acting as it should be as rynberg was talking about. In that case its just a matter of staying in the correct RPM range as I was talking about. But yeah, yours is a different problem.
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Originally posted by ptrhahn This is nothing "inherant" in a twin turbo system. The bottom line is, something is malfunctioning, and not returning the door inside the manifold to blow exhaust (almost) exclusively at the primary turbo when its supposed to, requiring you do do something "more" to trigger that action, like letting the car idle. I'd even think that its something vacuum or mechanical in origin, because given the sound of the motor, i'd say your ECU isn't delivering fuel and timing maps consistent with what the turbos are doing... in other words, if you TUNED for a non-sequential car, it wouldn't sound like that... the maps your getting weren't intended for the conditions, because those conditions weren't intended. Bottom line is, it's not "poor boost response" its poor or faulty system management... the door should be coming back, and its not... ergo, something isn't doing what its supposed to be doing. |
It can be both a solenoid problem and the way the PFC operates.
Watch the TCA solenoid in the sensor section of the PFC. It will stay on after you back out of the gas until 3K RPM. If the PFC shows the TCA solenoid is not actived but it seems to be stuck in twin mode, then you have a solenoid problem. I had the same exact issue. Sometimes the twin mode stuck on even until I came to a stop and it was the solenoid. After replacing the solenoid the PFC still kept the TCA open until dropping below 3K RPM which I confirmed by watching the TCA solenoid indicator on the PFC. To summarize: PFC says twin turbo mode then it wants it to be in twin turbo mode. If the PFC doesn't want it in twin turbo mode but it feels like it is, then you have a problem unrelated to the PFC. BTW. I switched to nonsequential soon afterward. Mark |
anymore inputs or solutions?
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Bump. I know this is old issue, but any solutions yet?
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I'm not going to run nonsequential... i'll stay with the system until such time as I go single.
Originally posted by vosko i know its not supposed to do it but getting rid of all the vacuum lines, solenoids etc simplified everything on the car |
I agree with that notion.
If I am going to go non seq, i mine as well toss all the rats nest and other do dads and go single. But, part of the charm of the FD turbo system is the low end power. |
Bump... I just found this thread after making a new post in the tech forum. I'm having the exact problem described here. My car didn't do it with the M2 ecu I had. Also, a couple of friends with almost identical setups don't have the problem.
Here's my post for reference: 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! - Dave Disney http://rx7.voodoobox.net |
You have eliminated any issue other than the way the powerFC operates if the Turbo Control Solenoid indicator is on when the boost takes a while to build and off when it doesn't. This is an output indicator, so the powerFC wants to do what you are complaining about. Contact someone with the datalogit to change the transition. You may want to call Chris Ott at rx7.com. He can explain what needs to change.
Mark |
from the autosportracetech.com site
Vacuum Chamber This is a black plastic tank that is buried between the alternator and power steering pump. Kind of difficult to see, removing the Pressure Chamber helps to see it, has one hose connection, and should have a hose attached, (Engine View Picture). This hose comes from the rats nest of metal tubes, and there is a one-way check valve between the rats nest of tubes and the Intake, (the only check valve located between Throttle Body and the Firewall). This one-way check valve can start to leak after a while, causing loss of vacuum to various controls when under boost for a while. A way to troubleshoot this one-way valve leaking is to note a gradual loss of boost and then drop the throttle long enough for your boost gauge to indicate at least 20 inHg of vacuum then slam the throttle back down again. If boost isn't back up to what it should be then replace this one-way check valve. Basically what this does is "recharge" the vacuum chamber when you let off the gas, allowing actuators to operate properly while the vacuum is still present. What about checking this one-way check valve they talk about above and seeing if that's the culprit. Tim |
The stock system low set point is closer to 3400 rpm, dropping below that will get single mode. At this point, the vac and pressure at the TCA is released/vented by the solenoids and TCA slams door shut, which is naturally assisted by pressure in the exh manifold. When I let rpms drop to 3500 still in twin mode in 3rd gear, the pull is still quite good and boost jumps. In 4th the rpm climb after decel is slower, so boost rise in twin mode will be sluggish up to 4k or so.
The usual PFC settings lower the twin on and off rpms, vs stock. This helps transition spike control by getting it done before torque peak, esp with high boost settings. But 3k sounds too low for an on point .... i'd start increasing the low rpm setting (and high if a min delta is needed). As others said, make sure a slow-when-hot solenoid is not delaying the low point venting for the TCA. Also need to be sure CCV is closing near the y-pipe for single mode. |
Originally Posted by almost99
You have eliminated any issue other than the way the powerFC operates if the Turbo Control Solenoid indicator is on when the boost takes a while to build and off when it doesn't. This is an output indicator, so the powerFC wants to do what you are complaining about.
Mark I going to give the check valves another look and test them with a vac. pump. If that doesn't turn up anything, I'm putting a remote camera in the engine bay and watching the actuators and compare them to a car that operates properly. I'll report back on what I find. |
Anyone figure this out?
I am actually having this problem as well. I've posted under another topic a week or so ago that stated after I get into the 2nd turbo and shift I am only getting 2-3 psi. Well I read this and had to go out and do some testing and if I push in the clutch and let it get to below 3k and floor it again my boost is fine. Just letting off the throttle to allow vacuum to build back up doesn't help at all. I have to wait till the rpms get back down. I am leaning towards a sticky actuator but I must admit I am not sure which one but I do know what its not. All vacuum/pressure lines are fine. Pressure and vacuum chamber are fine. All solenoids are fine, I've even swapped them out with others and I get same results(Hot ones is the only thing I haven't tested). I have replaced the TCA since the old one did have a problem but it didn't fix this issue. I have tested all other actuators and when the car is cold they work within specs. CRV and ABV are also fine. Since my TCA is new I am ruling that out. So does anyone think that either the pre-control, wastegate, or charge control could cause this? If someone can give a good argument for one I'll buy it to test. I'd love to get this system working properly. |
Yep.
I'm still having this issue. I'mn sure it's something small and simple to remedy. But to diagnose it is a bitch. |
strange mine does not do that...
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having similar issues myself.
I managed to get the car to run great for about 2 days then its back to running shitty. I have terrible boost response int he lower rpms and i also have this dreaded transition problem as well. Its almost always something stupid and miniscule.But to find its a bitch indeed.Let me know what you guys find as any clue would be quite helpfull.Im thinking at this point that its probably a leaking vacuum chamber or perhaps a bad check valve.But how would this affect my primary boost? especially at low rpms? i thought the system was quite simple as far as primary boost is concerned. |
It's kinda scary when it hardly boosts in lower RPMs and then wildly shoots up towards the top.
When the boost character was normal it was easier to let off on the throttle if the engine starts to knock. |
Update:
Decided to check things while they were hot. So I ran the car for a bit and then dug into it. All turbo related solenoids checked out ok. Both the 12v test and the ohms. First actuator I tested is sticky. CCA. Previously I did the kokoko test and the vacuum test and it never appeared to be bad so possibly it being hot made the difference. Problem is I have a funny feeling this isn't the problem but I hope so. At least it will probably fix my jumpy transition. I'll order one tomorrow since its bad and will report back once I get it on. Sometime next week probably. Pre-control and wastegate actuators appear fine. Didn't check the TCA since its new, or if I am more truthful, I was too lazy to get under the car. :) |
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Arutha, do u have pics of this?
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My comment might be out of place because I might not be sure of what's happening here for many of you but I have great turbo response at all RPM ranges (except in 1st gear, a little slower response). I have manual controllers and bypassed the solenoids all together. I couldn't believe the difference when I made the change. I watch the boost gauge jump almost instantly. I do have the PFC but my boost is mechanical now.
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Went single turbo! :) That took care of the problem. :rlaugh:
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No pics at the moment. But there are two metal tubes coming from the TCA area up behind the airpump. The sections that these are connected to with a hose are right beside and a little under the small coolant hose which is under the pressure chamber.
These are all just in front of and to the right of the wastegate/pre-control soleniods if looking at them from the front of the car. |
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