SubTX

Thank you, CamGTP. I looked at the misfires and found cylinders 1, 5 and 7 misfiring but #7 was the worst by far. So I'll look more closely at that cylinder. The connection to the coil looked good but maybe the coil itself is weak. I'll test that, pull the plug and also swap the O2 sensor.

I'll give that a try. Thank you.

I have an L83 with ~280,000 miles in a 2015 Suburban. It recently started idling rough, down shifting harshly when slowing to a stop and, intermittently, down on power and mileage. Sometimes the mileage is more normal but mostly it isn't. I'm just starting to diagnose this issue so I'm learning and learning what I don't know about these engines. I've only had the vehicle for about a year and this is the first LT engine I've worked on. I logged some data with HPTuners and I noticed that at idle and up to temp the timing is all over the place. Between 12 and 30 degrees. Is this normal? I also seem to have the bank 1 O2 sensor ranging from 38 to 800 mv while B2 is happily stable at 790-810 mv. This idle behavior "seemed" to start when I changed the spark plugs so I'm going to go back and check all the plug wires (again). I bought a coil pack and I'm working through all the coils to see if one of them is dead. I have an O2 sensor that I will swap for the B1 sensor. I've run a can of CRC GDI IVD valve cleaner through it and, while it blew out some stuff, it didn't make any difference. I plan to run another can through it soon. I have a P0300 code but that's not specific enough to get me to the offending part. I have the HPTuners log file if you want to see that. I'd appreciate any ideas for a direction to trouble shoot or what are common problems for these engines the I've overlooked. Suburban1.hpl