I'm at a loss, so I need help I'll try to be as descriptive at possible because I know its hard to diagnose a problem over the internet. For awhile now, I've been throwing a P0420 code. I can't figure out how to get rid of it because it is so general of a code it really could be anything. I only developed the code a few weeks after I got the car back from the 2010 bday meet. I'm not out to blame the tune or the tuner again I'm just trying to cover all the info. I was coming home and I was trying to make a stop light when I felt what felt like, a IC pipe blowing off. I limped it home and popped the hood and found nothing. After that, the car never made it over 15 psi and started throwing the P0420.
When I state that it never makes it over 15 psi I mean that when it hits its not steady its almost like the boost gauge needle bounces away. (This is the only way I can describe it.)
So what did try to fix after I got the code ?
Front O2 sensor,
exhaust manifold gasket ( turbo - manifold ) <- I ended up cracking that gasket in half.
Intake manifold gasket
Throttle body seals, Throttle body gasket
I removed the EGR and the additional lines that came off the back of the intake manifold.
I haven't done a boost leak test, I'm building one, I haven't done a compression test either because I just thought of it. I'll do one tonight when I get home.
The only thing I have to offer as a information are the AFR readings:
When I'm at idle I see it anywhere between 16.5 - 17.9
When cruising I'm at 14.7 - 15.9
When I'm in boost 13.9 - 12.4