Hello, I a having a heck of a time with my Silverado missing. I have been fighting it for the last month. I finally have it to one code a P0300, random misfire. I ran a data scan for 11 cycles with it just idling. I got ign advance of 3.5,3.0,5.0,2.0,5.5,6.5,11.0 12.0,11.5,12.5,11.5,15.5. Should the timing change this much at idle? Also, when I pulled the 4th plug wire out, the plug came out. I threaded it back in. I was showing a miss on cylinder 1, but that seems to be not showing up. One last thing, the other day, I got a flashing CEL and couldn't get it above 1500 rpm without it missing like crazy. Thanks.

 

what engine?
the flashing mil is from the misfire condition.

the easiest way to do this is to monitor the misfire counters with a scan tool. this way, you can isolate the problem to a specific cylinder or cylinders.

 

It's a 4.8.