rossc

I've been trying to figure this problem out for awhile with no luck, so I figured I would throw it out there and hope someone had a similar problem and a fix.

Problem: At WOT before 4500RPM (ex. 4th gear pull from 3000RPM) the boost builds to about 10psi (sometimes small spike to 11psi) but then immediately drops down to 6psi, then back up to 10psi, down to 6psi etc. You can watch the boost needle do these pulses at about two 10psi to 6psi to 10psi cycles per second. The problem is worse with more throttle (aka. the bouncing is 10psi to 8psi with a little less throttle). PLEASE REMEMBER THIS IS NOT A PRIMARY TO SECONDARY TRANSITION PROBLEM.

I have a boost controller (BCU+ unit from Performance Import Trends). I know everyone is going to flame the controller, but I've used them on other cars with no problems and prefer them to previous HKS controllers I've had. If I set the controller to a level of 0psi, the car of course has perfectly stable boost at about 8psi. The problem only occurs when I try to set the boost higher (ex. 10psi). And yes, I've tried pretty much every tuning combination possible for the controller.

I only want to run 10psi, but I had to install the controller due to uncontrollable boost previously (15psi and up). I'm figuring the wastegate solenoid was shot.

TPS is in range. All couplers checked for leaks. (pretty sure it's not a boost leak since the car could boost 15psi before controller install). Silicone vacuum hose used for wastegate, turbo pre-control, and on pressure chamber.

Mods:
Cold air intake
Cat-back exhaust (JDM so no pre-cat)
Greddy blow-off valve (tested, not leaking)
MINES re-mapped ECU
A/F, boost, water temp gauges

Any suggestions?

rossc

Someone has to have some idea?