hi , i just got a new (2nd hand) rx7
I have noticed that while driving sometimes when the 2nd turbo is supposed to kick in it doesn't have boost and keeps at 0 psi. the first turbo always kicks, and when the second fails the car looks like a non turbo vehicle.

Any hints about what it can be?

 

Make sure your vacuum lines are connected.

 

^ that's pretty vague... which vacuum hoses? connected to what?

1st of all, don't panic because it's most likely a control problem rather than a physical problem with the turbocharger.

you're basically going to have to teach yourself how the system works and how to diagnose it. it's a painful process, but when you've gained this understanding the car is alot less frightening to diagnose and work on.

good link: http://autosportracetech.com/RX-7/Tu...leshooting.htm

Your precontrol actuator controls boost before transition and your wastegate controls post-transition boost.

You may have a large leak after transition... maybe check your charge relief valve... it could be venting boost from both turbos back to the airbox by staying open after transition.

What is your boost vs RPM pattern like (should be 10-8-10 with the 8 happening at 4.5k rpm)? Do you hear air rushing when your boost drops to 0 psi? Can you hear the turbos spinning after transition?

 

sometimes i do hear a rushing sound after i release the accelerator, if i start from low rpms the second turbo always kicks , it faills usually on high rpms.
if im running on 3rd gear @ 3000rpm and i floor the accelerator the second turbo will go in but when i shift to the fourth gear it may loose boost

 

What kind of shape are the vacuum lines in? How many miles do you have on the car right now? Sounds like a vacuum leak or a control actuator not working right. Could also be a loss of pressure from the pressure tank or vacuum chamber. One is on top of the motor and the other is buried between the power steering pump pulley & alternator.

 

It is pretty vague, but in the same respect if one of the many connections is disconnected then that may be a simple solution to the problem. It seemed like a logical place to start.

I had a similar issue as yours. It turned out to be one of the vacuum lines under the vacuum chamber (near the upper intake manifold) was disconnected from the hard line. The primary would boost all day, but as soon as the secondary was suppose to kick in the boost would drop to 0 psi and the car would act sluggish. Reconnecting this one hose solved the issue.

 

Alexdimen provided an excellent resource, as I assume the OP did not do a search prior to posting this thread.

Let the OP do his research and see what he diagnosis...

 

Check the vacuum lines that go to the big fat actuator for leaks.

thewird

 

I had a problem with 2nd turbo sporadically or partially kicking in. It turned out to be a hose blown off the pressure chamber. The TCA (turbo-control actuator) uses both vacuum and pressure (one on each side of the actuator diaphragm to get enough force) to actuate. If the pressure chamber is not holding pressure (various reasons such as leaks, disconnected hose, bad check valve), then secondary boost will be sporadic, depending on what you were doing just before transition.

The vacuum chamber affects many other things also, so, since you have good primary boost, it is not likely the vacuum chamber causing the problem.