Boost fluctuation...Please help me fix this...dyno graph within
 

OK this is a boost problem that I have had for a year and not even my local RX-7 guy can't help me resolve it. I posted a thread a year ago and it got lost but now it is just plain driving me nuts. I rarely boost the car anymore because of it.

It only occurs when the secondary turbo comes up to peak boost. It seems as though the wastegate solenoid or the wastegate spring is ineffective at maintaining peak boost and therefore it fluxuates. Once it hits 10 psi it drops back to 8 then returns to 10 and back and forth all the way to redline. I want to have my car tuned better but it is near imposible as well as embarassing putting it on a dyno while it does this. Here is a pic of the dyno that shows the progression of the boost as well as its dips. The peaks represent full boost and as you can see the valleys are the dips it keeps doing over and over. Do you think that a seperate boost controler may resolve the issue? I have changed out the wastegate solenoid numerous times with ones that I know work to no avail. Please help! http://www.can-amf1.com/jmarvel/dyno.jpg

Get an electronic boost controller. The controller's solenoid will replace your wastegate solenoid and offer you control over the sharpness of response.

I had thought that as well. Thanks for the input. Since money is tight right now due to a coolant line leak and having to have it repaired is it possible that a manual boost controler would suffice until I got enough money to buy a nice electronic one?

A manual boost controller will not solve your problem. All a manual boost controller does is vary the amount of boost the wastegate actuator sees. It sounds like you are having an issue with your wastegate solenoid/actuator, which would only be solved by installing an electronic boost controller with it's own wastegate solenoid. A Profec B Spec II controller can be bought for around $300, preferably you can find a used original Profec B in the $200 range.

This assumes that you are not having some other kind of mechanical issue that is causing the wastegate to flutter like that.

Also, if you install a boost controller, you will have to adjust your boost settings on the PFC. You will need to raise your boost target settings to a higher value than your boost controller is set to, to avoid fuel-cut.

I ran across this thread searching on another matter and thought I would contribute my own experience.

I also had fluctuating boost after the secondary hit peak. I have eliminated the the flutter using a MBC and bypassing the WG solenoid. I suspect the cause of the problem is in the PFC...perhaps the settings in the boost control menu or its learning mode.

Maybe I'll reconnect the WG solenoid and explore that when I get more time.

a problem like this has been happening to me... I assume ur still using your sequential system? your best bet is to rip the UIM off and start testing solenoids to see if they hold pressure and they switch properly. I've managed to narrow down mine to the turbo control solenoid, the one with the mistubishi symbol on it. you can test the solenoids with a mity vac or you can ghetto rig something up (which i did) if the mity vacs arn't availible. to ghetto rig you can do like so

solenoid====vac T===one way check vavle=====hand pump=====one way check valve

and on the vac T you connect a boost gauge or something.. this was just to check to see if the solenoid was able to maintain holding around 10-11 psi of pressure. To my amazement most of my solenoids couldn't hold that amount and began to leak slowly. you also need to check if the switching mechanism on each solenoid works. do this by simple hooking them up to a 12v source and you should hear a click and if it is still hold pressure all the pressure should be quickly released. In total there should be around 4 main solenoids to look at. The charge control, charge relief and the two turbo control solenoids. IF you haven't changed them i think they should be ones with a white (charge control), two brown dots or something (charge relief), and black dot (turbo control), and the two nipple'd mistubishi one (turbo control). The main thing is to check every solenoid and make SURE that they are working properly before finally putting the UIM on. I've been going back and forth changing stuff and it is NOT fun.

things to also check, make sure the back lines running to the turbo control actuator are snug. And that little flapper door on the ypipe is working fine too. Also make sure your check vavlues are flowing in one direction.
fluttering flutter fluctuation bouncing unsteady second turbo problem. sorry just adding those things in for future searches of people.
the best bet if you don't want to deal with unsure parts and dont' want to go to mazda and spend like 60 bucks on a solenoid is to see if anymore of the upgrades solenoids are being sold. There were done on some kinda group buy thing and i'm sure they'd work better than anything we are using at the moment.