Hey guys. I need your help once again.
Just did an engine swap of a ej20k from an STI version 4 into my wrx version 4. (the old engine spun a bearing. what a suprise)
my issue is, I get some pretty aparent hesitation as boost builds up. from say, 5psi, right up to peak boost. once peak boost has hit, the hesitation completely disappears in an instant and I get hit by an anvil of 276hp.
on steady accelleration in high gear, the hesitation sticks around for as long as you stay between 5, and 16psi (JDM ecu)
on further analysis, the turbo seems to make a slightly different noise when the stuttering is occurring, similar to the sound the blow off valve makes on release, but much, much more subtle, and in line with the typical turbo noise.
boost stays steady the entire time, eg, when the hesitation is occurring, the boost does not drop or jump.
things changed:
one way oil breather valve replaced
canister one way check valve replaced
MAF replaced
Cleaned the MAP
cleaned IACV
switched to manual boost controller
rubber washer test on knock sensor (to see if the issue was caused by excessive knock detection)

none of these seemed to have helped.
Cheers for your time
Will make a video tomorrow.

 

Clean bcs?

 

Tried completely bypassing it with a MBC. no avail. will add it to the list of things tried

 

Different bottom end,
Different compression ratio?
Have you mapped it since the rebuild?

Oh and how long ago did you rebuild?

 

you misunderstand. not a rebuild. direct swap. ecu, motor, turbo etc.

 

How many miles since the engine swap?
Any engine mods?