Here's what I have found so far.

I installed a boost gauge a couple of weeks ago, and
testdrove my '93 touring (a K&N drop-in airfilter being
only modification). Boost pattern was very consistent 10-5-8 in third gear.
Vacuum at idle was about -17 inHg.
Primary boost was very immediate and robust.
At aroud 4500 rpm it goes down to 5 psi briefly and recovers to 8 psi almost immediatly.
So the primary turbo is fine, Check. Boost leak somewhere? Not likely but possible as always.

So the Next day, I did search the forum and found trouble shooting method mentioned by rpm pwr.
I found another trouble shooting by P'cola FD (teeing into vacuum hoses) but I haven't gone through it yet.

OK. So I turned the key from ACC to ON, and I could hear some clicking sound from area under UIM and from the primary(front) turbo area. But not from CCA (charge control actuator). The CCA rod was pulled OUT (CCV open) and didn't move when my wife turn the key to ON. So I checked the vacumm hoses to CCA and CRV(charge relief valve). No sucking sound. Ah, there was no vacuum. That was why the CCA rod was pulled out and didn't pull in when key turned to ON.
I test drove again, looked at the CCA rod. Then the CCA rod was pulled in (CCV closed). And it stayed there even when I turned the car off. I tried to pull it out with a screw driver but it pulled right back in. There was vacuum in the line connected to CCA and I could hear it when I disconnected the hose from the nipple.
The Next day, I looked at the rod again. Then the rod was pulled out as before. No vcuum in the line.

From all those observation, I guess the CCS (charge control solenoid) is not switching vacuum/pressure to the CCA. And the vacuum is slowly leaking out to atmosphere over time. Or is it the CCA itself that doesn work properly.

Any idea from you experts are greately appreciated.
Sorry for the Long thread.
Thanks.

 

Oh, I forgot to ask this.
If the CCS is indeed the cause, where can I buy one?
I don't see any Mazda dealer around Ann Arbor, MI.
Thanks.

 

Check your PM's.

 

You wouldn't happen to own a white FD would you? I saw one when i was driving around a couple of weeks ago parked around UMich campus.

Anyway, I had the same boost pattern before, and after I changed my precat to a downpipe it went to 10-8-10. Now it's back to 10-5-8, and it may be because my main cat's getting clogged as well. I plan on looking into it this winter.....

 

I too had a similar problem, and like Alien7 I fixed it with a downpipe. Downpipe is probably the best thing you can do for the car anyway, so it would be worth it even if it doesn't fix your boost problem. Just be careful with boost spikes after you install it. Most people don't get them with just a dp, but I did. Had to change the pills.

Also like Alien7, I now have other boost problems which someone suggested was related to a clogged catback or main cat. Right after I hit 10 psi on the second turbo, it drops to 8 again. It can't hold at 10psi. Also, sometimes boost builds very slowly (never gets past 4-5 psi).

 

What and where is the CCA at? I'am getting the CRV and the CCA mixed up. I need to check mine to see if the rod is moving in and out but don't know how?

 

Even with no vacuum system at all you will still get full boost on the secondary. I know I sound like a broken record with this but check you CR. Take the CRV hose off the airbox and go for a drive. It should be loud as hell from 3000-4500 in third and then just shut up. If it keeps rushing then the CRV is stuck open. If it shuts up then you either have a boost leak (check the secondary turbo -> CRV hose) or the cat is clogged.

-pete