LS1 wont fire

[02fiehawk]

Have an LS1 Firehawk. A couple of months ago, the battery went dead. Jumped it and it ran but not well. The alternator was not charging. I got a new battery. About 2 weeks ago, I was backing my car into the garage and my son told me something was coming out of the exhaust. I took a look and it was paper and stuff that a mouse had in there. Thought I got it all out. I attempted to take it for a drive, the Service Engine light stated flashing and it was idling bad. Put the scanner on it and it threw a misfire on cylinder 8. Cleared it, it then ran better. Few days later pulled it out of the garage and the car was running bad again. Threw codes: misfire on 3 and o2 sensor. Cleared it. Took the muffler off thinking it was clogged. Ran better a couple of times when I pulled it out of the garage. Now wont fire. Am at a loss. Any help would be very much appreciated.
Cars is immaculate and only 19,000 miles on it. All original

[blue02Z]

hmmm... is your fuel pump running. it coulda been taken a dump and was not supplying enough fuel, hince the misfires and o2 code for running lean. i'd verify that you have fuel pressure, you can do that on the end of the fuel rails. if the fuel pump is working but no pressure, check the fuel filter. also check for spark on all plugs with a spark tester



also welcome here!