Hello, I have turboed my car only a month or 2 ago, and have been driving it fine, fixing small things before the big tune. The other day my car all of a sudden went to 10 AFRs and even at idle and cruise. The next day it started fine, and after a couple minutes of driving started getting super rich again, until it got to 10 AFRs and lower and started sputtering. I checked the engine codes to day to see if it is my front O2 sensor, but it read code P0420, which I looked up and says its to do with the EGR system. Anyone ever have any problems with that and know a fix or a way to see what is wrong? I checked the vacumes to the EGR valve and they are all fine and not leaking.. Please help, thank you.

 

Actually i think it threw code P0401.. But the symptoms do point to EGR since it goes super rich when car heats up.. Let me know, thankyou.

 

P0420 is a code for the cat

P0401 is insufficient egr flow
could be a bad egr valve, carbon build up, vacuum problem

 

p0420 is a common code, when you dont have a cat anymore..

And sounds like a fouled o2 sensor...

/thread

 

So should I replace the front O2? or EGR? The main symptom is the car goes full on dumping fuel when it warms up... Goes from cruising at 14s to 10..

 

p0420 code is for the secondary 02 sensor...like mike said its common when not running a cat. a fix for that will be to either weld in a cat or use an antifouler (things that are ment for spark plugs to keep them from being oil fouled) on the secondary 02 sensor. search for antifouler on here and youll see exactly how to do it..its no biggie. However the rich condition you are experianceing has nothing to do with the secondary 02 sensor nore the code p0420.
It is possible the primary 02 sensor is fouled or damaged. Im leaning more towards it being a tune issue. You said it ran fine for a little while and now its all rich huh? if thats the case try this, disconnect the batt for a min and reconnect and see if its back to normal. if it does then its tune and your tuner will be able to correct the issue. good luck and happy boosting

 

Do we even have an EGR valve on the tc? I mean its only used to control NOx. But there are other ways to control it as well, like exhaust temps, and the 3 way cat thats now employed in modern cars.

 

https://www.scionlife.com/forums/tc-tech-diy-1818/antifouler-cel-fix-header-45083/


follow that and replace the second o2 sensor.