I have a 1999 K1500 Surburban with a 5.7L V8 and 138,000 miles. I purchased the vehicle late last summer and It was starting to run rough in the spring so I replaced the cap, rotor, wires (AC Delco parts), spark plugs and later the fuel Injectors. those changes appeared to work, but now 3-4 months later I'm now having the same misfire/hesitation when I start the car, after driving 5 minutes it smooths out.

codes are as follows:
First: P0304 cylinder misfire #4

Then if I keep driving a few times/days I get:
P0155 O2 sensor bank 2 sensor 1 (heater circuit malfunction)

In the repair manual it talkes about the O2 sensor not being hot enough to monitor the air fuel mixture until the engine heats it up. The electric heating circuit in the O2 sensor just helps heat it up faster. So, when its cold "The ECM/PCM controls the fuel metering based on the inputs of other sensors and its own programs." wouldn't that then take the O2 sensor out of the loop and not affect the performance on a cold engine? What would cause it to hesitate when the engine is cold and then run very smooth once it heats up (about 3-4 blocks)? I plan on replacing the O2 sensor since it is throwing a code, but I don't think that will solve my problem. Any ideas/suggestions would be appreciated. I"l let you know what happens when I change the O2 sensor tomorrow evening.


Thanks,
Frank

 

Update: I did replace the O2 sensor in front of the cat with no luck. It still ran rough when cold this morning. I need to pull the spark plug and see if it is fouling.