Rich00Yukon

Hey all, I joined this board just now because it is the most comprehensive one that I found on the 'net with regards to the GM late-model V-8 engine family. I have an '00 Yukon with the 5.3L engine. Today I started it up to leave work and it was running rough. Then the SES light came on. I scanned the codes and got P0304-cylinder #4 misfire and P0157-post-cat 02 sensor voltage low bank 2. Changed the #4 plug and wire and it was no help. Now I was going to change the coil pack but now I am wondering if it could be an injector problem. I am thinking that the 02 sensor code is being triggered by the misfire. I know that low 02 voltage is caused by a lean condition which could be because cylinder #4 is not getting fuel. So, what do you guys think since you all have experience with this sort of thing? Is it the coil pack or the injector? Any info or troubleshooting suggestions would be greatly appreciated. Thanks.
--RICH

etc

can you swap coil with another and scan to see if it misfires on another cylinder ? that would narrow it down. i'm sure you've tried injector cleaner or pulling the injector and cleaning it. check wires to injector ,coil for damage. sorry thats all i've got

Rich00Yukon

I have not pulled the injector yet. I will do that and clean it tomorrow. The wires to both injectors and coil look good. I will also try the coil swap if possible. I ran out of light and time today. Thanks for the help and advice. Anyone else want to chime in?