Yet more boost questions

[framey]

Hi guys, need your help please.

I\'ve searched and I think I have a similar problem to this..

http://www.mazdarotaryclub.com/forums/showthread.php?t=16280

ie no or very low boost on the second turbo.
My problem is that boost is fine on the first (8-9 psi), it then drps to abot 5 @ approx 4300rpm. Just when I\'m expecting transition to hyper speed, the boost drops to abot 3psi, and stays there.

There has been talk about the wastegate opening taking boost away from the turbo\'s. What I want to know is what could cause this and how can I fix it?
Is there any way I can temporarily disable the wastegate to verify?

It seem\'d fine when I collected it from pip\'s after he replaced the turbo\'s.

(btw \'92 3rd gen std set-up, no mods, just a powerflow exhaust and wgt hi flo cat)

Recently I have noticed a hissy/screech under heavy throttle, but if I had a leak, why am I getting good boost on the primary?

Thanks in advance.

[TonyBlair]

Hi mate,

I\'m afraid I don\'t have any real good advice to help you diagnose your boost problem. However I would recommend you have a look at the following website; http://rx7.voodoobox.net/ Check out the "how to\'s" section of that site, it\'s pretty useful for dianosing boost problems.

I\'m actually trying to resolve boost problems on my car at the moment. All I\'m doing is replacing all the vacuum lines and the turbo control solenoids (the rack of 8 that sits on top of the block). I\'ve read that a lot of boost problems occur due to split/collapsed/baked vacuum hose, or faulty solenoids. Which is why I\'m replacing them all.

If I still have boost problems when I\'m done then I\'m clean out of ideas. I doubt very much that the turbo\'s themselves are at fault since they were only rebuilt about 2000 miles ago.

Sorry I can\'t be much more help than that mate. However I would recommend replacing the vacuum lines and solenoids. It\'s the kind of job that will need doing eventually anyway.

All the best,
Jon

[jonrx7uk]

The most common cause of no secondary boost is a vac pipe coming off of the pressure chamber (black plastic thing between air pump and alternator).  Have a quick look, there should be 2 going into it on the passenger side of it..

Cheers
Jon

[TonyBlair]

I *think* this is ther pressure tank - someone correct me if I\'m wrong please.

[Fish]

Hey Tony Blairs got something right.... Oh hang on its a different Tony Blair.

Fish

[framey]

Thanks for the pointer guys - this is a definite possiblility as I had the alternator off not long back - I\'ll check it tomorrow.
Thanks again.

[adib]

my second turbos the same tryed lots of things it will work once and then gone thinking of pxing it for a mini lol

[K1HKS arse]

In short -

Primary turbo has to work properly before the secondary can.At 4500rpm secondary turbo should cut in.You should see 10psi primary then at 4500rpm as secondary cuts in will go to 8psi and within 1-2 seconds should go back to 10psi on secondary.Transition between primary and secondary is controlled by solenoid in rats nest that needs to see pressure and vacuum at the same time(pressure tank on top of engine as shown and vac chamber front right hand side of engine).
Check primary turbo is working perfectly first,plumb up temporary boost gauge if you havent got one already (need this to check proper working).If this proves ok then move on to rats nest/plumbing,vac and pressure chamber connections,check for pipes off or split.
Check all pipes and hoses,common faults are Y pipe coupling split or loose,secondary actuator above secondary turbo on y pipe not working or bad connections.
I could go on forever to be honest,got to go to work now.Will check back later.

Gary
GA Racing Developments

[framey]

Ok, well in desperation I took off all the intercooler piping to try and find the root of this problem.
Checking all the couplings I thought all was ok. before putting it all back on I decided to have a closer look. Eventually found a split in the top coupling (between the airpump & Alternator), this was only visible when the coupling was bent or streched.

So I guess when I said I was getting full boost pressure on the primary, I was mistaken. With it all connected back up I was getting 10+ psi.

So now the car feels fantastic- better than I can ever remember actually - one extremely happy bunny here!
Thanks to all for the advice given.

[framey]

By the way, does anyone know where I can get new couplers from? I\'d like to change all the couplers on the intercooler and intake (hard pipe) lines.

Cheers