[IIvega80]

I recently got my 2015 civic si (full bolts ons with RBC swap and j37 TB) tuned, when it was being dnyo tuned it sounded great and made 225WHP. After a couple of hours it started running like crap, it bogs and hesitates around the 2k-3k mark and feels like it’s not performing at it’s best. I Went back to my tuner he couldn’t figure it out aswell and ended up sending the logs to hondata, it came back as being the crank position sensor. So long story short I’ve changed that, the O2 sensors and it’s still the same. On top of everything it isn’t throwing no CEL.

 

[BWill9886]

You've checked all your vacuum hoses?

 

[IIvega80]

Yup just got done checking all of it

 

[BWill9886]

A bad PCV valve would be something to look into. Counterfeit spark plugs could be a culprit (If you've changed them recently and the new ones didn't come from the parts store or manufacturer). I think we can assume it's not the knock sensor, as you'd likely see it in the logs.

Another avenue is checking the condition of parts you've added. What condition was the J37 TB in when bought? The downpipe have any cracks? What injectors? Were they used? Have they been tested at all? Aftermarket or OEM fuel pump?