Installed high flow cats and after like 4-500 miles got a SES light. I know there might be a slight exhaust leak on the driver side cat connecting to the y pipe. The cats have 90 degree bungs for the o2 sensors. So it would be an air intake leak or maf sensor problem? Or is it just because the exhaust is more free flowing?

 

More likely a exhaust leak. Make sure you don't have any leaks on exhaust system before doing anything else.

 

yea I ordered z1 gaskets cuz the ones that came with the cats weren’t the best. I assume I have to do an ecu reset after making any changes for the code to clear right?

 

Yes ,after all leaks are fixed clearing the codes will be necessary

 

I installed hfcs and there’s a slight leak between the driver side cat and the y pipe, I used the gaskets that came with the cats they’re fast intensions. Gonna buy the z1 gaskets but they look exactly the same, would I be better off trying to use a gasket sealer instead?

 

It's actually more common to have a leak where the cat meets the header. You can try the gasket sealer method