RZRX7TT

Guys i think i have a boost problem, but my so called MECHANIC think i dont. Ok here is the problem, now this is building boost below 4000 rpm first, ok i am in first gear and go moderate throttle i dont get 10 pounds, more like 4 pounds and then it drops down to zero and i dont get anything through the whole rpm range in first gear, in order to get any boost i have to mash the pedal now when i switch into second gear and go moderate throttle i get 6 pounds. Same scenerio the boost builds then it drops to zero and i cant build it back up. If i wait and build vacuum in second gear then go into the pedal, i get 10 pounds, but lasts again for a small period, before it drops to zero again. The drop always happens when i hit 4000rpm as i keep the pedal at moderate throttle it stays at zero. When i am in third gear i go moderate throttle, i get 10 pounds for split second, before it drops down to zero. Same scenerio in order to get it back up to 10 pounds i have to wait for a second build vaccum then go into the pedal and i get 10 pounds. The boost drops to zero when i am at 4000 rpm and above, and in order to get back i have to either build the vaccum as i described, or i have to mash the pedal to get 10 pounds. Now 4th and 5th gear is usually the gears where i shift into when your at 4000rpm and above, now when i switch into 4th lets say at 4500rpm i go into the pedal moderatly it goes to 10 pounds then it drops off to zero! in order for me to bring it back up i have to build vaccum again then go into the pedal and i get 10 pounds. 5th gear i will get 10 pounds. HERE IS THE MECHANICS THEORY. Mechanic says that first gear YOUR NOT supposed to get 10 pounds, true or not true? and he says that second gear and third gear, in order to get 10 pounds you have to build it below 4000rpm and then you have to go full into the pedal in order to maintain to redline. NOW for some reason i dont believe this **** at all, he is telling me that you can only get 10 pounds below 3000 rpm and then you have to go full into the pedal to have to redline. Give me a break so if i am at 4000rpm and i go into the pedal i wont get 10 pounds, this is sequential, arent you supposed get 10 pounds anytime? what you guys think? WHATS CAUSING THIS PROBLEM!

CanadianRex

Dude, is this Marco that's telling you this? I don't have the answer, but I have a hard time believing that Marco doesn't know how your car should run and would tell you that there wasn't a problem if there was. Usually mechanics are the opposite and tell you that is a problem when there isn't, unless of course it's still under warranty.

I always thought that you would only get 10psi at WOT as that would be the only time you need it. If you aren't using the boost, why would it be there. Again, I don't really know as I still don't have a boost gauge to tell you if mine does the same. What caused you to think there was a problem....is it just because your gauge doesn't read what you thought it should, or is there a noticable loss of power?

I hope that someone knows the right answer to this as I am quite curious, partly because Marco is also my mechanic.

RZRX7TT

hey canadian rx! whats up man, yeah well for some reason i disagree with markos theory that you have to build ten pounds below 4000rpm in order to have it through out the power band, because that sounds more like a single turbo setup, with sequential you should have constant boost through the power band, from what i believe is a slight drop at 4000 rpm when the transition goes from the primary turbo to the secondary turbo. I dont know, but canadian rx get that boost gauge and maybe we can compare, see what your getting, but i diffinently feel their is something wrong with my boost.

jumprdude

If you find yourself in the situation where you're having to wait for vacuum before being able to build boost, try checking the check valve leading to your vacuum tank. If that's leaky and the tank is not holding vacuum, that would cause boost problems.

Good luck.

RZRX7TT

yeah i pulled one of my hoses off and i got air rushing out so the pressure chamber is holding pressure, any other suggestions?

spurvo

Not pressure chamber, VACUUM chamber. Specifically, the one behind and between the alternator and power steering pump. It is fed vacuum from the rats nest through a check valve. It provides the vacuum signal to the turbo control. If the check valve is not sealing anymore, when the engine goes into boost, there will no longer be a vacuum signal to the turbo control, it will close, and you lose boost. When you drop throttle to shift, vacuum comes up again hard enough to actuate the turbo control, and you get boost again, but it fades again as the vacuum from the throttle lift is used up.

look here for more...

http://www.autosportracetech.com/RX-...leshooting.htm

RZRX7TT

what color is this one way check valve that runs to the vacuum chamber, anybody have a pic that shows this one way check valve or a site that has a pic of it? by any chance is it silver?

RZRX7TT

bump

spurvo

I'm pretty sure it's one of the green and white ones, Mazda part # 13-995. The silver one should be the purge control canister line's check valve. I think it needs to be metal so it doesn't dissolve in the fuel vapors.

As to which specific green and white, I'm not sure, and I have no picture, so ultimately, I'm useless to you!

RZRX7TT

SPURVO your not usless at all, i really appreciate you coming back to check my post and reply, we need more guys like you on this forum, thanks for your reply man.

shred

Well here is my take on the advice that you have from the mechanic. You will always have some degree of boost from the turbo's. You are just bypassing the boost to the air box until you hit the gas enough that will lock the bypass's off (no vacume in the intake). And the computer controlling the waste gate using the boost sensor in conjunction with the TPS (throttle postion sensor). The rest is that very complicated crap that Mazda put in there for Sequential Turbos.

So to put it short and sweet, yes, once at the right spinning speed you have more then 10lbs of boost in the turbos, its just how your bypass and valves control it to lock the right valves and switch over to the right turbo that applies it to your motor.

From first glance, I would say you have a vacume leak somewhere, a check valve either backwards or not working, your bypass valves are not closing correctly, your TPS is messed up, serious computer problems, boost sensor is messed up and the list goes on and on.

Best that I can say is that it isn't right. You should have more then 10lbs on a good set of turbos except at low rpm and at the crossover between the two turbos.

RZRX7TT

well lets put it this way i get 10 pounds at low rpms but if i am at high rpms say like from 4000 and on and i give moderate throttle i get 10 pounds than it quickly drops to zero and then wont go back up, i have to mash it to get 10 pounds and hold so it wont drop to zero, does this help at all for trouble shooting?

LAracer

What do you get in the standard WOT in 3rd test? I get boost roughly proportional to the amount of throttle I give; only 10psi at WOT. If I let off the throttle completely the boost falls to zero. Can't remember what happens when I go from, say, full to half throttle. I'd guess that I'd see 0psi as the bov opens (the bov is either open or closed, nothing in between). I think this is the kind of thing you're supposed to see.

I'm with jumprdude; check your vacuum chamber and check valve: Go for a drive, then the next day disconnect the hose at the front of the check valve. You should hear air rushing into the hose. Or, better yet, get a vacuum pump ($20, Autozone) and connect it to that same hose. It should hold a vacuum for an indefinite period of time. The check valve should allow air to flow only one way (toward the UIM).

Good luck.

redrotaryrock8

well, if your mechanic knew even a little bit about 3rd gen rx7s, he would know that below 4000 rpm its the primary turbo that does the work, and after that its the secondary.

so, if you have problems after 4000 rpm, the problem is pretty clear. get the mechanism on the secondary turbo checked- preferrably by someone other than your current mechanic.

also, when he said, your not supposed to get 10psi in first gear- ask him to f**koff and never touch your car again. on an average you will make more boost in lower gears.

my guess is that you have a problem with the vacuum hoses.