[jwallycars]

Having issues with 2003 Nissan Sentra (1.8L) running rough and blowing white smoke out the tail pipe. Check Engine light is on. Brings up codes
P0304, P0420, and P1278. Focusing on P0304 Cyl 4 is misfiring. Coil is good, spark plug is good, injector is good, fuel pressue is good. I get spark on all cylinders. I checked the compression and it was around 130 so I also checked cylinder 2 and received a lower reading. The reading should be about 190.

I took the spark plug out on cylinder 4 and stuck a screw driver down into cylinder to make contact with the piston. I pull it back out and there appears to be an 1/8 of an inch of oil on top the cylinder. I know the piston is not firing because I disconnect the fuel injector for cylinder 4 and it continues to idle rough just as it was previously. I disconnect fuel injector for cylinder #2 and it really idles rough as expected.

The head gasket has just been replaced. The head was checked out as good.

Any ideas on next step for this problem? Thanks, Jim

 

[i68k]

p0304 - general misfire on cylinder 4
p0420 - cat below threshold, cat failure
p1278 - Air Fuel Ratio Sensor 1 Circuit Slow Response Bank 1

its not good that you have oil on your piston. you need to find out how that oil got there, there's only 3 ways for oil to get onto your piston. assuming you didnt drop oil thru the spark plug hole, we can eliminate this way. the only other 2 ways for oil to get on top of the pistons are to seep thru the headgasket, or pass over the piston rings. so either headgasket or piston rings could be bad. does it drink oil or coolant?

i wouldnt worry about the p0304, its just a misfire and you can clear it. you p0420 means you have a bad catalytic converter, but for the ecu to determine this, you need good readings from a pair of o2 sensors. however, your p1278 is an o2 sensor code. it is for one of your primaries which would control your afr. the code is for slow response, so maybe it just need to be replaced, it could be caked up or something, maybe from the cylinder 4 junk. check the connections to it, make sure theyre plugged on tight so its not just losing voltage.

make sure your battery terminals are super tight, and you have good ground contact. check your voltage motor on & off. just to be sure youre not getting all these codes due to lack of voltage.