BATMAN

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.

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.

BATMAN

interesting.....

ptrhahn

iTrader: (9)

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...

ZeroBanger

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.

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.

BATMAN

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.

pomanferrari

iTrader: (1)

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.

ptrhahn

iTrader: (9)

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 **** 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.

ZeroBanger

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.

reza

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.

BATMAN

My vacuum hose should be fine since I had the full silicon hose swap.

CCarlisi

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.

ptrhahn

iTrader: (9)

Grounding is something i hadn't thought about... i'll bet mine isn't the greatest.

What exactly did you do and where?

Tim Benton

iTrader: (1)

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

rynberg

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.

CapitanCombo

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

CapitanCombo

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

ZeroBanger

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.

vosko

iTrader: (4)

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....

ptrhahn

iTrader: (9)

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.

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.

ptrhahn

iTrader: (9)

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.

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 **** as any non-seq people will verify.

artguy

sounds like a sticky actuator issue.



j