I have a 99 ex with a 00 b16a2 swap,with a mugen chipped obd1 p28.i recently had the motor rebuilt and put it back in myself,but now vtec wont work.the car runs fine when at normal driving oil level is fine so i know its not oil pressure.what are all the possible reasons that vtec dont work.and yes there is a check engine light on wile driving

 

see what the cel is

 

Some codes that the ECU throw disable vtec.. find out what that code is and get it fixed.

 

u said its a p28 chipped with a mugen chip? and your check light engine comes on?, usually its the ecu with the chip, the chip is either messed up or so, i had the same problem b4 too and it was my ecu chip, the tiny legs broke off.