so i just installed my brand new shiney JBP vortex header two days ago... while i had the catalitic converter out it has a slight rattle to it... so i tipped it upright and small amounts of "sand" fell out, now i know that this is a sign of a cat going bad but this gets better.... so after i put it all back together i have an exhaust leak at the gasket where the header and downpipe meet.... right next to the o2 sensor... so i pull the new gasket out and it is already blown out just from a ride around the block... so i put the old metal one back in and now it leaks less then the other but still leaks... in the exact same spot as the first one (right next to the o2) so i figured i'd just get another and double it up (it has been ordered)... well on my way home from school today i did a WOT run and my car falls on its face at 5,500 rpm and at 6k doesn't move just holds a constant speed.... so i did another run and watched my boost gauge and at that point my boost goes from 12psi up to 18+ and then i got a blinking CEL... so i shut the car down and restarted it and the light went away and i haven't ran it since but it drives normal...

is the exhaust leak causing this to happen or is the cat partaly clogged and causing the exhaust leak?

 

Pull the cell. If your cat is clogged that would add to the backpressure and hence more boost. I think you have nailed the problem. I think the cel was just for the overboost and that is why it went away. Good luck.

 

so today i had some time at work to play with my car a little bit... i checked out the CEL and nothing... no history... no signs of anything... so i decided to try and find out if my cat was actually bad... unbolted the flange after the downpipe and cat.... went and drove it... still hit 15 psi (instead of 11) but didn't fall on its face so hard... so then i went back and took the down pipe off and ran just the header... perfect 11psi boost and never lost power all the way to red line... so then i buffed both the flange surfaces and made them all smooth and pretty.. got my gasket back in there and bolted it down... checked it out... no exhaust leak... so i was thrilled... went out and drove it and next thing i know my gasket is blown again... and i'm still hitting 15-18 psi....