As the title says, i have a problem with the boost after 4500 5000 rpm. The boost pressure stays around 0.7bar and it pulls just fine, but when reaching 4500 - 5000rpm it drops until about 0.3 and the noise from the engine changes to a more growly noise. I also have to slow down until i get vacuum before i can floor it again. If i dont slow down i also get 0.3bar boost all the way..
Is this a valve not opening so the second turbo doesnt come alive or?

 

test the check valves

 

sequential or non-sequential? mate o mine has this same problem with non-sequential....

 

I've had a problem similar to yours. Took me nearly a year to solve the problems because i took my time. I Found that I had a few bad check valves. One from the vacuum tank and the other from the pressure tank. Later I found that the pressure tank it's self was leaking. All acuators past the test and I was going to save the best for last......the solenoids. When checking the turbo its-self first I found the secondary turbo inlet pipe was really loose. I thought if thats loose I bet others are loose two. Sure enough even the primary turbo outlet to y-pipe bolts were loose. Surely its got to be the same for the secondary turbo, But You have to get under the car to remove the secondary inlet pipe. Once that was removed My suspicions were correct...The Bolt had worked itself off the secondary outlet to y-pipe and there was an 1/8in gap. So when the transition was supposed to happen all i heard was whooooooooosh from under the hood and a boost drop to 4-5. Bolted everything back up and went for a quick drive that ended up lasting over an hour because I finally felt what this car is supposed to feel like....................definitely worth the pain of troubleshooting.
For me it was'nt just one thing but a host of things. The sequential mechanics are complex.....add 17 years to that, usually more than one thing is not working.


Here are is a great link for the trouble shooting:

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

Vacuum tank and or pressure tank simple leak test:
http://www.youtube.com/watch?v=OfAlNNPGtXo

I took some pictures while under the car and of the secondary turbo outlet to y-pipe gap. A little fuzzy but you get the idea.

 

Thanks!
I have tested the check valves and the pressure tank. But no luck. But i had no pressure on this tank after a test drive. Isnt this tank suppose to store pressure all the time? im guessing the solenoid that is leaking or something

 

No pressure in the pressure tank means either a bad check valve, a leaking solenoid, or a torn/loose/leaky vacuum hose. Rarely it could also be a leaking pressure tank. It could certainly explain your lack of boost.

Have a look at the vacuum hose diagram and branch out. You're looking for anything attached to it. If you have a vacuum / pressure pump tool (in the US we can get a tool called a Mityvac) now is the time to use it.

Diagram:
http://www.davidgeesaman.com/rx7/93v...lor.edited.jpg

David

 

i found out after some testing with a bikecyclepump, pressurizing the rats nest that the turbo control solenoid was broken, leaking through letting all the vacuum out of the system. This is the second solenoid i have to replace.. Hope this will fix it

Im thinking of just bypassing this solenoid just to try it out to see if the secondary turbo kicks in. Will this do any damage ?

 

This is something I went through and the problem was solved when a friend of mine Abdul used his magic hands (no homo) to solve the boost issues I had, I have a after market boost controller and it was having a conflict with the stock boost controller, so through the Power FC he disables the stock controller and SHAZAM! The runs like a champ now.