My secondary turbos (new J-spec twins) are behaving strangely after the 4500-rpm switchover. The secondaries don't seem to come online with full boost; they only make 5 psi boost after the switchover. If I lift off of the gas after the switchover 4500 rpm, then squeeze down on the gas again, the secondaries come online like they're supposed to, up to full boost to 8000 rpm. The Power FC is set to 0.95 kg/cm2, 86% duty cycle for both primary and secondary turbos. The strange behavior happens with 0.85 kg/cm2, 76% wastegate solenoid duty cycle; and 0.80 kg/cm2, 74% wastegate solenoid duty cycle. Is this a bad secondary turbo blow-off valve? A sticking wastegate spring? Wierd Power FC behavior? I'm frustrated! I've searched, but the difference with my problem is that the secondaries DO make boost AFTER backing out of the gas, and then squeezing back down on the gas to get the proper boost pressure built up to redline (8000 rpm). See my sig for mods. FWIW, the J-spec twin turbos are only 5000 miles old. The hose job has already been done. The motor is only 5000 miles old. All the gaskets are NEW. I have a new Efini Y-pipe

 

Manny, this could be your problem:

(this is from http://www.autosportracetech.com/RX-...leshooting.htm )

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 is 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.
The vacuum one-way check valve goes from the Intake manifold to the Vacuum Chamber via the rats nest of tubes, (Mazda Part# N390-13-995A). This has a layer of three paper like filters on each end for separating any oil from the air.

 

Yes these are the symptoms. It's like I have to double pump the accelerator to get the secondaries to come on to redline. If I leave my foot to the floor, I hear boost venting (the tell tale whoosh, whoosh, sounds). The motor still makes power, and tach climbs, nicely, but not as nicely as when the secondaries are online with 12 lbs of boost to 8000 rpm

 

Heh, even from Mazda, the check valves are less than $40 -- which is a damn cheap repair for this car! I hope that's your problem because that check valve is easy to get to and replace.

 

rynberg,

I looked under the pressure tank. Lo and behold I'm missing the other half of the check valve. It's apparently in two pieces. One half is attched to the pressure tank. The check valve half shows the three paper filters that filter out the oil. I'm not sure where the other half of the check valve went. It must have blown off of the rat's nest nipple, which is missing a hose, so this must be the culprit. That explains the whistling sounds under high boost too!

Anyhow, I'll replace the pressure tank check valve, and perhaps the vacuum chamber check valve (not sure where that one is located though).

 

This is what happened to me too....Took me months to figure it out (not to sound like a complete idiot but I had just bought the car)....It was the most annoying thing. I crazy glued mine back together until I got a new one and it worked.

here's the little biatch with crazy glue smothered all over it

 

apneablue,

I can't open the pic, just a little red x in the corner of a big square?

Which check valve was bad? The pressure tank or the vacuum chamber?

 

I presume this is the one that's located underneath the pressure tank? At least that's the one with half of the check valve missing, and a rat's nest nipple with no hose attached--in my case??

 

This is what happened to me too....Took me months to figure it out (not to sound like a complete idiot but I had just bought the car)....It was the most annoying thing. I crazy glued mine back together until I got a new one and it worked.

here's the little biatch with crazy glue smothered all over it

 

This is what happened to me too....Took me months to figure it out (not to sound like a complete idiot but I had just bought the car)....It was the most annoying thing. I crazy glued mine back together until I got a new one and it worked.

here's the little biatch with crazy glue smothered all over it



BTW, the the vacuum chamber doesn't have a check valve...So you'll only have to spend $40 not $80 Here's the Vac Hose Diagram for reference.

 

This is what happened to me too....Took me months to figure it out (not to sound like a complete idiot but I had just bought the car)....It was the most annoying thing. I crazy glued mine back together until I got a new one and it worked.

here's the little biatch with crazy glue smothered all over it

 

hey i might have that part if you want it. pm me and i will look for it when i get home. not 100% sure. i am running non-seq. is it a check valve???

 

and it's free if i have it. hope i didn't throw it out.

 

It's either the pressure tank, vacuum chamber or one way valve problem.

Oops, looks like you figured it out already! I can finally remove this bag from my head!

 

Where the hell were you when I needed mine?

EDIT: Sorry for the tripple post above...as you can see, our stupid @$$ satelite internet is acting up today. Mahjik, could you delete the unnecessary ones pweeeeesssse? danka!

 

Actually not yet. I do plan to replace the vacuum chamber...any ideas on how to go about that? I'll have the part in midweek...

 

When I did the hose job, if I remember correctly you have to take off the alternator to get to the vacuum chamber...I never had to take mine completely out but it should be pretty straight forward.

 

Yup, thanks apnea!

 

Man, I was just about to give up on my recent boost leak. Ive check all the hoses, zip tied anything questionable. But never looked at the check valve to the vacuum chamber. *fingers crossed, hopefully thats it.
I think it is.