running lean

[los]

was wondering what can cause my car to run lean ? help throw me a check off list to what can be the cause :mcry:

[Euro-Yellow-Ep3]

A lean A/F ratio is caused by a lack of gas compared to air. Cars run better lean but it will also harm your motor. Causese can be :

Changing to a bigger throtle body
Changing to a bigger Intake mani (RRC, RBC)
Header/ Exhaust
etc.

[superchargedk20]

Bad o2 sensor

[mitchlikesbikes]

Bad o2 sensor

yeah that.

[sleepy ep3]

Important question. How do you know it's running lean? What gave you that information?

[los]

well i got a cel code p0420 which i looked up and got that it was an 02 sensor or something with the cat so thats why i think its running lean plus even the exhaust smells funny like its not burring the gas right

[dkid15]

Ohhh interesting... Well If you exhaust smells funny your cats probably bad. Problem is thats indicated by your secondary o2 sensor. The only o2 sensor that reads the AFR is the Primary. Which is more than likely what is causing you to run lean.

You want a checklist. Either
1. Either get a race header and get rid of the Cat (I see your in cali though)
2. Your less desireable option would be to replace the cat and see if its fixed. The cat is bad, you know it for sure. Might as well start there before dropping more coin on the primary o2 only to have there be a less chance of that being the issue.

[dkid15]

Important question. How do you know it's running lean? What gave you that information?

Also this, Seems like you don't have kpro. How do you know its lean?