po0420 code

[Flyin '85]

Guys,
Wasn't sure if I should post this here or in the tuning section. Anyway, Ive got an 11GT that just threw the po0420 code this weekend which is the code for catalyst operating below efficiency threshold. Mods are.....Paxton blower, JLT big air, id1000's, stock mid pipe and corsa exhaust. Tuned by Mike Post.

What has me concerned is that with the corsas you can see right up the muffler. Both were always black not overly sooty, made 629 rwhp like this, ran awesome. Since it threw this code, I am seeing that the passenger side muffler is turning a real light ash grey, almost white obviously indicating that it is much leaner that normal. I did some reading and I've heard that this can be a fairly "generic" CEL. Sometimes it can be caused by faulty oxygen sensor/sensors.

My question is ....Typically the front oxygen sensor is the one the controls the actual AFR command which could cause the lean condition I have if that sensor is bad or could it be the back one which is basically there to monitor cat function and doesn't really control AFR from what I understand but could give me the error for catalyst efficiency. Ideas ???

Thanks in advance guys !!!!

 

[Blazer707@TBR]

If you meant P0420, then either you have a bad cat or your tune needs to be adjusted for an o/r mid pipe.

 

[Flyin '85]

Hey Blazer,
Thanks for the reply, I actually bought all the stuff on the car from you guys with the exception of the mufflers. I still have the stock mid-pipe so the part about the tune needing to be adjusted isn't the problem BUT you may be onto something with your comment about a bad cat. Would that make the car lean ??? Or at least appear lean looking at the exhaust ??? I haven't been driving the car hard b/c I don't want to kill something if it is in fact lean. I took it about the about 5 grand in 3rd yesterday just to see what it would do and it felt super flat....

 

[Blazer707@TBR]

What I would do is pull the cats off and visually look at them, if a cat is bad usually you will see it melted/broken. Look on the front portion, I would advise not to beat on the car or drive it if you have a bad/plugged cat. I've seen this on a bunch of boosted cars and they melt cats and can damage the motor if ran a lot.

 

[Flyin '85]

What I would do is pull the cats off and visually look at them, if a cat is bad usually you will see it melted/broken. Look on the front portion, I would advise not to beat on the car or drive it if you have a bad/plugged cat. I've seen this on a bunch of boosted cars and they melt cats and can damage the motor if ran a lot.

Thanks Blazer, that's what I will do. Like you said I've been really easy on the car, just basically putting around with my kids in it to see if it would throw any other codes. I'll pull the mid-pipe off and have a look.

Thanks again !!!
Jason

 

[Blazer707@TBR]

No problem. Let me know what you find out.

 

[Flyin '85]

Blazer you were dead on bud passenger side cat is blown apart. Just wanted to update the thread for everyone and give you some credit for being dead on. Thanks again and you have PM