Misfire with O2 sensor connected

[Keith Adams]

I hope someone has a suggestion for my issue.  I have a 05 Silverado 4.8, I have an issue with the engine misfiring after engine is warmed up if I am sitting in traffic or shut engine off and restart after a few minutes. 

 

I took the truck to the shop, after looking at it for two days they said the ECM was bad. They had a GM service manual which says if you disconnect the 2nd bank 1st O2 sensor and the misfire goes away, replace the ECM. With the 2nd bank 1st O2 sensor disconnected the truck ran great, 300+ miles not a single issue. I purchased a rebuilt ECM from a quality company, motor ran great until I connect the O2 sensor,  back to running horrible. 

 

Has anyone ran into this problem, ever seen  anything like this? 

 

Possible the new ECM also bad?  

[rjgti]

what codes do you have.  I assume your lean with o2 unplugged.  can you check your fuel trims.  what do your spark plugs look like. 

[davester]

With O2 sensor unplugged, he'll be running in open loop mode, completely different fuel tables.  Not likely to be useful for diagnosing what the problem is.  He'll need to diagnose it with the sensor hooked up.