So i have a high flow cat on and have had it on for 1000 miles no CEL light or anything...then today i let my friend drive my evo around my neighborhood and i told him to downshift to second and he accidently downshifted to 4th and we were going like 15mph. So the Engine got that loud rumble like its ready to stall since we were in such a high gear going so slow, but we got out of that. Then 8 feet down when we stop at a stop sign the CEL light comes up. Do you guys know what i should check for or do you know what went wrong?

 

See what the code is for the CEL.

 

lol true i should probably do that...my first thought was the cat but i can't really think why the cat now but yea ill get it read

 

head over to vato zone

 

the CEL is your friend, id def find out why its on and fix,

 

Just so you know, high flow cats aren't a fix all solution. They can still trigger a cel and some are still illegal for road useage. You shouldve checked the code even before posting. Your guess is as good as anybodies.

 

all right i got the code Pulled and its PO429 any insight on what i should do?

 

P0429 catalyst efficiency

just erase it and see if it comes back now.. and dont let your friend drive the car

 

lol i deff. won't let him drive it... thanks guys

 

hey it keeps coming back after about 60 miles or so, what should i do?

 

Install Tephra v5.10 and enable the rear o2 simulator

 

explain in more detail, what is this app?

 

does anyone know a thread where it lists all codes?

 

https://www.evolutionm.net/forums/sh...ad.php?t=69304

in the 3rd post there is an attachment..... the code you have is in there

 

spark plug defouler bored out to 1/2 inch worked for me

It pulled the sensor out of the flow of exhaust

cost about 2 bucks