hey guys and girls i have a mildly modified evo 8. with only bolt on parts.

it has the following:
Map NZ EF3 turbo
Link G4 ecu
Link boost control
Link 5 bar map sensor
1000cc dynamics injectors
Walbro 255lph fuel pump
HKS air filter
HKS ssqv blow off valve
custom 100mm thick intercooler
custom 3” intercooler piping
custom 3" intake
3” Apexi N1 exhaust system
Custom ported exhaust manifold
3” Apexi downpipe

it has been tuned to 20 psi low boost. all work was also competed just over 2 years ago and has travelled 17,000km since

i have reset my defi boost gauge and it boosted to 1.2 bar. once it reached approximately 5,000RPM it will "jerk a little" as if boost is coming on and off. i think at that point the boost gauge fluctuates quickly between 1-1.2bar. before this use to happen it would reach 1.5 bar. its also a struggle to get past 5000-6000rpm. it jerks so i just shift into the next gear and back off. iv only done this a couple of times to try figure out whats going on.

i have visually inspected
*vacuum hose to the BOV from the intake manifold,
*hoses to the link unit in the engine bay
*boost control solenoid
*hoses from the solenoid to the wastegate actuator
*hose from the solenoid to the turbo
*pod filter
*intake pipe
*removed intake pipe to check the turbo impeller for play
*intercooler piping
*removed and disassembled the BOV
*downpipe does not have a fexi so that couldn't have collapsed
*iv checked receipt from previous owner and ceramics have all been knocked out and cleaned in the cat.
* iv also disconnected the boost control solenoid. reached 1 bar and would not go any further.
reconnected boost control solenoid and still have the same issue but it would go to 1.2

and it all looks OK to me but I'm not a quaffed technician.

iv done my best to try describe the problem sorry if my description isn't very good.

any help, suggestions, advice, recommendations is much appreciated and i thank you in advance

 

Check your Spark plugs and make sure they're not fouled. I wasn't reaching full boost when my spark plugs were fouled. Also you also stated you have a 5 bar map sensor. You should try and log your car with evoscan and make sure your gauge isn't off. You also said your're only getting 1.2 bar. You should be at 1.4 to be at 20psi. Good luck