Hi everyone.
About a month ago I posted about engine knocking on my 04 Suburban 2500 - 8.1L. I ordered a reman'd engine and installed it. It's running great, but there's 1 issue. I'm getting a P0300 - Random/Multiple Misfire. The plugs and wires are new, in fact, got the code and changed the spark plugs again thinking that was the issue. It only occurs when cruising between 1400 and 1800 RPM. Idle does not trip the CEL, nor does acceleration. The CEL will go off when sitting at a light, and come back on once I'm at cruising speed and the RPM are between 1400 and 1800 again.
Does anyone know what this could be from?
Should I run a re-learn cycle on this since it's a new engine?
Since it's new, will it go away after x-amount of miles?
Just looking for suggestions, thanks in advance.


PS, the original knocking was a spun rod bearing from running it too low on oil for too long. The leak itself was coming from the oil cooler lines.

 

My standby is run two bottles of Techron thru it.