Having problems with my rsx. I change out the starter since it dead on me. After that car won't start. change the ground wire and car starts fine. Was testing the car out to see if anything was wrong. So took it out for a run and was redlining at 7200rpm. The check engine been on but when i first had it, it the cel been on and was redline at 7900. Got any idea what is wrong? The cel throws out p0420.

 

Did you disconnect the battery when you took everything apart to change the starter?

Clear the code once and take it for a spin

then stop abusing your car and fix the problem causing your CEL.........