now that i have put a test pipe on my car the check engine light saying bad catalyst reading or whatever comes on, anyone know how i can prevent the check engine light from coming on while still using the test pipe?

 

What test pipe did you buy?

You need to make a mechanical o2 simulator to prevent a CEL.

 

 

I have the CEL fix on my Invidia TP. The ECU took about 4K miles before it finally accepted thats just the way it is and hasnt been on for about 3K miles, including one 1200 mile trip a few days ago.