Hello,
I recently got an 03 Evo VIII with 20k miles, completely stock except for a short shifter and i'm having a boost issue. I've searched the forums for a long time now and can't seem to find the answer for it, so here's my situation:

I'm spiking at 15psi and holding steady at 14psi during full throttle. I've come to know that stock boost is in the 18psi/19psi range and tappering down to 16psi is normal, but during the week i've had my evo i have not gone past 15psi of boost.

My first reaction was my boost guage was faulty, although with running such low boost i've been getting some unbelieveable gas milage, so i'm assuming there isn't a problem with the gauage.

any ideas? thanks a lot.

 

possible causes are

Boost leak
Faulty Lining from Boost solenoid to wastegate actuator, or compressor housing.
Faulty Boost solenoid
Faulty wastegate actuator or wastgate
Blown turbo
and many others.

Check them in that order.

 

check the stock boost hoses.
chances are, it had a MBC before and the owner put wrong lines (without restrictor pill) in his attempt to make it look like stock.

The stock hoses have a restrictor pills in the lines.
If it's missing the pills, you will only see wastegate pressure which is only about 15lbs of boost.

 

Thanks a lot for the help you guys. The odds of the past owner putting the wrong lines in is most likely.

I'll begin my process of elimination of what the problem could be.

 

this is the part number for the correct hose mn143555.
The hose have the pills in them.
Just remove the hose that is connected to the BCS with this hose and you should be all set.

There is a T connection. one part goes to the wastegate and the other goes to
the turbo nipple.

Good luck.