I just put on a new high flow cat and a new muffler and since then every now and then the check engine light comes on, code po 420. I know it has something to do with air passing from the cat, could this just be because of the new cat? Should I just put a o2 simmaltor on or could this be something i should have looked at? I have a evo 8 at 90,000 miles.

 

It's a very common occurrence with the mod you did. The upstream and downstream O2 sensors are monitored for a certain balance. You have "upset" the balance the system is used to looking for. Solution - I dunno .. I'm sure others will offer some up.

This URL might give you a better understanding of what is going on:

http://www.aa1car.com/library/p0420_dtc.htm

 

yes get an 02 sim or perform the check engine o2 "fix" . for the 'fix' you will need to search around for the write up on how to do it. I did one on my Evo and it worked with not cat at all up untill I did a turbo upgrade. It cost about $5 and a small amount of free time. I think you can find more info on EvolutionM.net

 

this will fix it
https://mitsubishiforum.com/forum/sh...ad.php?t=14196

 

that what I was talking about. I cant access the DIY section it shows up empty when I go in there so I couldnt link it

 

Mike, you have to change the display settings at the bottom of the page from "last month" to "begining" since all sections are defaulted to only show the past month to reduce loading times and such.

You can also change this setting in the userCP to have it always show threads to a curtain date

UserCP >> Edit Options >> Thread Display Options >> Default Thread Age Cut Off

 

alright cool thanks guys i will give that a try