2006 silverado V6, hard cold start, runs rough cold

[Jerry C]

I think I got snookered. Just bought a used 2006 1500 silverado with a V6. Ran great during the test drive but it was already up to temp. SES light was on and owner said it needed an O2 sensor. Issue 1, hard to put in fuel. Gas Pump kicks off easily and multiple times. # 2, Hard to start cold(in Fla) it's not cold. Crank and crank. # 3 when started runs rough till up to operating temp.. # 4 While checking out the downstream O2 sensor, noticed that someone has cut open the catalytic converter and welded it back up. Took to autozone and got codes P0056,P0060, 0161,and Po300. As I was told the first 3 are the second or downstream O2 sensor. PO300 is misfire which it does plenty of.
With the Cat cut into and who knows what they did, will replacing the sensor even help? Previously I have read about the fuel vent issue and it's seeming intense fix.
Any order to attacking this mess? Thanks, Jerry
PS, I have already replaced the cabin blower resistor board and harness to bet the blower to run.

[Blue Bowtie]

Welcome Aboard!

It's good that you read the trouble codes as that provides good clues about the problems.

By the description, the PCM may not know what the exhaust oxygen content is, until it is fully heated, so the problem with the oxygen sensor heater circuit needs to be resolved first. If may just be a failed connection, or the sensor itself.

Since the O² heater is evidently not operating the sensor will take quite a while to reach operating temperature and provide a good signal to the PCM. Until then, the engine runs on backup fuel parameters, which are usually (necessarily) extra rich. The resultant rich mixture and possible fuel fouling is likely the cause of the random misfire code.

[Jerry C]

Thank you Blue Bowtie.

I will start down that path.

My biggest concern is that the Cat has been opened up, what they may have done there. Obviously remove or smash enough to get exhaust gas to pass the Cat? That said, If the downstream O2 sensor works , will it ever get a satisfactory reading? Thanks, Jerry

[Blue Bowtie]

If the cat has been gutted or burned out it will likely set a P0420 (Catalyst Efficiency) but fuel trim, spark advance, and operation should return to normal.

[Jerry C]

That means that I should replace the O2 sensor.

[Blue Bowtie]

That means the sensor needs to be investigated. As previously mentioned, the sensor heater circuit malfunction could be only a connection.

[j cAT]

the 161 code means the downstream pass side O2 sensor has no current flow to it/ open circuit... also possible fuse and wiring shorted/open..

examine the O2 sensor wiring if it is cut/repaired then just change it.

on the fuel filling this is usually a plugged up fuel tank vent solenoid or the vapor lines are damaged from the canister being plugged up..this happens when the vehicle is over filled with gas and then is parked.

converter cut up never heard of that .. perhaps it was damaged by some object ?

so it runs good in closed loop ... but when below operating temp like 165 F the engine is running rough >>.

that can be many other things fix the code issues first.