Boost Problems with FD3S

[Iwan]

Hello,

what I want to say first. I'm new on this forum comming to it from advice of Glenn. I'm from Germany, so sorry for my broken english.

What kind of problem do I have.

Well first to tell:
I was changing my standart blowoff (air bypass valve) to Apexi valve. I was removed the charge relief valve and changed the vakuum hose (from manifold) to it, couse the old one was not OK any more. To change the valve, I needed to remouve the air pipe from the Y-Pipe to the intercooler. To remove this, you need to remouve the vakuum chamber.
After all this, I have a problem with my boost. What exactly?:
By driving the car, the maximum boost riches about 13PSI for very short time. Than the boost drops to about 8PSI and never comes to the 13 PSI again. After all this, I have had removed the Apexi BOV and build everything back. The problem is still present. I was checked the charge relief valve, and have replaced it (well it was not deffectiv), the problem still remains. I have read that the both solenoid valves, the wastgate control, and turbo precontrol, are there to regulate the boost. I have checked them and I have replaced it (them was not defectiv to). The problem is still there. I have checked my vakuum tubes, there are no dameges on it.

What I think is, that the ECU don't get new settings from this two valves. I was trying to check the cabling. I could found as follow:

I have on the B/W connector the batary voltage. On the L/W is nothing. There is resistance between the L/W and B/W. The value of resistance is depending on, if the ignition is on or off. So I thing there should be working cabling to the ECU.

But the problem is still there,,, I dont know where to look after once more...?

Do you have an idea, where I should looking as next?

Regards Iwan

[alistair bridge]

hi,

firstly i must compliment you on your english, mein deutsch ist nicht so gut.

i dont know a lot about fds, but they have twin turbos designed to cut in one after the other. ie first turbo cuts in and boost builds to 11 psi (factory standard) but the turbo is small so it cannot flow enough air at higher engine speeds and the boost drops to 8 psi. this is when the second turbo kicks in. mazda were tring to avoid turbo lag by having two small turbos rather than on big one.

from what you have said i'm not sure you have a problem.

hope this helps

alistair

[Iwan]

Hi Alistair,

thanks for fast replay.

Well, there must be a problem. I have heard about, that the system is going back to about 8 PSI. Befor I started changing something, the car was making about 170 miles an hour. But now, I dont get the car above 150 miles..

The boost drops as follow:
when accelerating, pushing accelerator pedal to the ground, the boost comes up to about 13 PSI. After about 2 seconds, still pushing to the ground the boost drops to about 8PSI. The results are, like getting from the pedal at a half. The acceleration drop.

The 13PSI are resulting in using downpipe instead the first catalytic converter. My FD is one of the first FD's made, so this is one of this FD, that were going better, than FD made after. (more boost??) By looking at your mazda parts, there a section for FD build from 1991 (!!!) to 1993. The cars made after, are a bit different. You can see it on plastic that was used.

I was checked the error codes by shorting the "TEN" pin to the ground at diagnostic box. But the check engine light was remaining off, means there are no errors.

I was trying to finde a Mazda dealer in Germany, who owns the DT-S1000. But fineshed without success. With DT-S1000 I would be able to simulate the funktion of valves. Especialy of the charge control, turbo control and charge relief. Them are the next I will check.

Regards,

Iwan

[alistair bridge]

ah, just read your post properly and the second turbo is not cutting in...not that i'm telling you anything you didn't know.

you should be able to check solenoids by applying 12v and blowing through them. if these are all working, i'd start inspecting the wastegate actuator and the second turbo. sounds like it just isn't doing anything..

sorry i am not much help

cheers

alistair

[Iwan]

Hi Alistair,

you right, I was not writing about the second charger. The second charger is OK. At the time you accelerate, the second one comes about 4.800 RPM. But the second kick, ist not realy what you should get. By accelerating (not matter at which rpm, but above 2.300.) normaly by pushing the pedal, the boost comes to about 12PSI. Not in my case. It still stops at about 8 PSI.

I will check the actuator for precontrol and wastegate control. (duno how to check them at the mom)

I was in hope, not to remouve the manifould. But seems I have to do so. :(

Regards
Iwan

[alistair bridge]

checking an actuator is simple. use a bike pump to slowly pressurise the hose that goes from the actuator to the charged intake. this should make the actuator move. if it doesn't the the actuator is dead also try wiggling the actuator link in case it is a bit sticky oh and like your 2ng gen, makesure it is attached to the wastegate.

cheers

alistair

[Iwan]

Hi Alistair,

what I'm confused about is, that at first time it works. I mean when the car comes to the normal 13 PSI boost first time, but the boost is drops than.
When the actuator wouldn't working correctly, then the car would not comes to 13 PSI at first. ?
I think there is everything OK with cabling couse the car is running at first moment. With defectiv cabling it wouldn't run.

It looks to me like, the ECU dont get any signal, so the wastegate solenoid valve don't open correctly. For the first time, the ECU takes old values, by accelerating it trys to get new values, but dont get new one or something like that ?

Regards

Iwan

[alistair bridge]

slightly confused by your post. i am assuming that each of the turbos has it's own actuator. not having seen one in the flesh i cannot verify this. it is the only way i can see that the car would be able to run sequential turbos.

the second turbo is not kicking in so check its actuator and the hoses connected to it and check the switching solenoid valve.

thanks

alistair

[Iwan]

Hi Alistair,

the second turbo comes at about 4.800 RPM but the boost stais at about 8 PSI.

"the second turbo is not kicking in so check its actuator and the hoses connected to it and check the switching solenoid valve."

I have done this.... I also replaced both solenoid valves. The next what I will check is the actuator.
But the first and second charger are there! So the actuator of both chargers should work. Only the boost is not present.

Regards
Iwan

[Iwan]

Remember that 7 PSI is a ‘magic’ number...it is the spring pressure of the wastegate. This implies that your control system is not controlling boost up to the stock boost level, instead you are building pressure until the wastegate spring allows boost pressure to bleed off. The spring is 7 PSI. If you have no control beyond the manifold boost pressure and the spring then boost pressure and boost characteristics would be limited by deltaP of the turbos and the spring and wastegate. Now, what Mazda did is add a bleed solenoid under ECU control. The duty cycle on this solenoid (and flow characteristics of the pill if you have one) control how much manifold pressure the spring actually sees. In simple terms (I don’t really know any others) if the ECU sees 8 PSI of boost it is programmed to bleed at least 1 PSI from the control system so the wastegate spring doesn’t open. [ It actually works the other way. The solenoid valve is kept open until boost is close to the programmed limit and then closed until the wastegate starts opening to keep boost constant. The fact that under static conditions this results in 2-3 PSI of pressure escaping from the control system so the wastegate spring is forced open is immaterial to the ECU. ] 7 PSI is ‘magic’ from the standpoint that if your control system is not working but your turbos are, you will get no more than 7 PSI or so of boost. The ECU bleed system is required to get higher values.

[t2rew]

if you do a search on the forum for twin turbo pack removal


youll notice that it has been spoken about before but with no real answers. sorry .

[Iwan]

...... seems to be a serious problem.

I will try to get viton tubing, and will than remove the manifold to check the other velves and tubing.

Will keep you inform.

Regards

Iwan

[t2rew]

Originally posted by Iwan
...... seems to be a serious problem.

I will try to get viton tubing, and will than remove the manifold to check the other velves and tubing.

Will keep you inform.

Regards

Iwan



yeah, please do. im sure it will be a usefull referance for others

[Iwan]

Hi all,

as posted before, I keep you up to date.

I removed my manifold at weekend. Now, I'm waiting for my Viton tubing. The 6mm one should arrive during this week. Now I need 4mm one, but did not found right one at the moment. Everyone can offer me 4mm Viton tubing but with only 2mm wall thickness. (think it should work also) I'm searching for tubing with about 3mm wall thickness for payable price. ( to never make this job again) (my best offer at the moment: 50meter for 22,76 EUR /meter = about 810 GBP! a bit to expansive)

Its craisy, in the US you can get 1/8" Viton tubing with 1/8" wall thickness for about 270 US $ for 30 feet. In Germany, you can get just tubing in "mm" and only with 2mm wall thickness. 1/8" cost craisy money!

Slowly, dont like this country any more....

Regards,

Iwan