Hey there! So, my 2018 Fit LX has 66,000 miles and has been great. Lately, it's jerky under acceleration especially until it reaches normal operating temperature. Last night the check engine light came on. This morning I scanned it and it had a PO420 Cat code. I did a cylinder AF test, and all cylinders except 3 were too rich. I changed the plugs with OE. The only thing alarming was the dark brown ring on the porcelain (I am guessing from blow-by gases) I swapped the 1 and 3 coil, cleaned the MAF sensor and did the test again. This time ALL cylinders were too rich. It still feels jerky under acceleration until it reaches operating temp. The code has not come back yet. The only thing I know to do is a smoke test to check for a vacuum leak, and possible adjust valves (though I didn't do my '08 until it had 100k, this seems premature?) I don't suspect a bad coil but I could be wrong. I hope it's not a bad injector or internal. Any ideas or experiences with this? Thanks in advance.

 

similar issues already being discussed
https://www.fitfreak.net/forums/3rd-...2500-rpms.html

 

Thank you!

 

My next step is to use the scanner to check fuel trim, and get O2 sensor data. Will keep you posted.