I just need help on narrowing it down on where to look if I'm only boosting at 4psi. Did a search and found that the Y-pipe rubber coupling could be the cause. I looked at mine and found that it had a small amount of oily residue around the lip of the coupling so I'm guessing it might have a leak. Just in case it's not the coupling, where else should I look? And also, what is "Limp Mode"?

 

Take the couplings off and inspect them, also take the lower intercooler hose off and check it. When the parts are installed, the problems are usually hidden from view.

My car had this same issue when I purchased it. The rear coupling and the lower int. hose were practically blown apart.

 

I just had the same problem, I fixed it by replacing the y-pipe coupler and I also found 4 solenoids including double throttle control to be bad and I also found a failed Charge Control Actuator. Its a very good possibilty its the y-pipe coupler, I did fix mine by replacing the mentioned parts above, I am very happy to say I have a normal boost pattern now. Good luck.

 

I just finished ordering a new coupler. I didn't realize that my rear coupler off of the y-pipe into the turbo was ripped until I actually took it off. Sometimes the y-pipe itself can crack...u can always replace it withe the efini y-pipe upgrade. Also check the intercooler hoses the accordian looking ones. Hopefully its not one of the solenoids. Good luck. Just take of most of the hoses and inspect them.

 

really have to check all of the couplers, my y-pipe coupler was ripped under the clamp and you couldnt tell that anything was wrong untill you were under boost. also, use a 2.5" silicone coupler instead of the stock mazda one, the stock is $55 and a good silicone piece is around $15-$20.

 

2.75 coupler is the y-pipe. I suggest ordering a high temp silicone 500 degree 4-ply coupler. under 10 bucks. You can go to Napa auto parts store for t-bolt clamps. They self torque themselves, very high quality. Rated up to 30+ lbs of boost. Just did it 4 days ago. Might have to ask someone working there.