I am having issues with knock on 91 pump gas with the stock spark tables on a 2018 gmc sierra 5.3 l83 A6 . Im honestly puzzled by it and am wondering if it's due to the lt4 injectors and lt4 fuel pump. It only happens under low rpms/high load. 3rd gear and up between 1100-1400 rpms when the engine is lugging for power. I've had to put negative timing to combat it. On the highway at 60mph I'm at 1150-1200 rpms. If i accelerate it will knock from 1100 rpms to 1400 rpms unless I make the truck downshift then there's no problem. If I run e85 I have no issues with knock just on 91.
What is going on? Any ideas? Is there anyway to increase the rpm at highway speed? I am pretty sure that would require new gears right?
My tuner said it was bad gas when it first started doing it, but that's not the case because it happens everytime I fill up with 91.
This was the tuners response about it "What happens is I bet you are in higher gear (4,5, 6th which has low tq multiplication) and lugging it which causes a high load low rpm issue with spark"