I have a 2001 cali jeep cherokee that failed emissions, the codes indicate bank1 on the downstream o2 sensor and misfire on cylinder 4. I tuned it up changed the o2 (3 times) and replaced an injector and added seafoam. I cleared the codes but after a short period the check engine light came back on with the same codes. The inspector then suggested maybe it was a fuse problem. all my fuses seemed fine. I have been trying to solve this for over a month, been pulled over several times but luckily, no tickets so far but I did get a warning so next time I will get one. If anyone has an idea of what's causing this issue please let me know. I have heard on this forum about "cheater" plugs and I am ready to try anything at this point to get it back on the road. If someone knows how to get these plugs, please let me know. My jeep runs great, just can't pass emissions. thanks in advance for any help. (driving me crazy).

 

Guess the new improved smart thing won't let you fill out your info or see links in sig's.
Where are you, and why were you jacked up? Sounds like you had your papers and made it through!

 

So you had codes for Bank 1 (cylinder 1-3), downstream O2 sensor and a misfire code for cyl # 4 (bank 2)? And when you did all that work both codes came back?

What did your tune up include? spark plugs? air filter? How many miles on it?

 

Check all injector wires (two per injector) for continuity on bank one... if these check good and you can hear your injectors clicking on and off, I would suspect your ECU.