mods : everything stock EXCEPT the airbox and spark plug wires

Airbox is ARC, and Spark plug wires is one of those stupid ones with an extra ground, I think it's Nology Hot wires its called ?

ok, on Stock ECU, car basically won't rev pass 4K, it goes to 4K, then it drops back down to around 2~ish K rpm, then sllowly comes back up. repeat. NO MATTER what your right foot is doing.

with Non-stock ECU, say, RE-Aimemya ECU, it goes up all the way to redline BUT the car backfires like nutz after 4K rpm. the backfiring ONLY happens under heavy load/wot, the car will not backfire under light load.


I'm thinking it might be a failed coil or it could be garbage spark plug wires that causing it. and it also looks like it's in limp mode.

what I know about the car is, it was put together by the owner (not me!)

so I have no idea if it was "right" in the first place, it's a new friend's FD, he has been having this problem for a while, it's my friend's friend.

I'm going to see if I can pull codes for his car in a day or 2. but any ideas what might cause it anyone ?

Thx