I got my flex pipe replaced and swapped the o2 sensor but It still feels sluggish while accelerating and the P0171 won't go away along with a p0420.

There seems to be a hissing sound when i accelerate that wasnt there before the flex pipe cracked

 

Time to replace the catalytic converter! But you can double check for holes in the weld when the flex pipe was replaced or the clamp is not sealing.

 

The two codes could be unrelated. I’m pretty sure P0171 means the car thinks the fuel trim required to correct a lean condition is excessive. So could the hissing be a leak in the intake?

 

I'll go ahead and check that out but most are saying its time to replace the cat. I'm told its as simple as bolt off the old and bolt on the new.

 

I just got one of those mechanic stethoscopes so ill check around that area. Is it comon to have a leak there?

 

Yes it is...........But....It's going to be an expensive part.
Since you're in California, you'll have to buy that "California" certified cat. One of our other members just posted a thread about those expensive cats. (something like $800 or so just for the part)

 

Oof, that one hurt...

Would you happen to have a link to that?

 

https://www.chevyhhr.net/forums/gene...nverter-65019/
(make sure to read the entire thread )

 

Wait a minute! How long did you drive around with the P0171? That can definitely be the cause of a melted cat. What happens when gasoline vapor hits something that is at over 1400 F?

 

ugghhh I'm not sure I've the CEL for a while now. This is starting to sound really expensive