spark knock

[slowmod'01]

I took a trip to Gatlinburg TN this past weekend in the Explorer, there were 4 of us plus luggage. I noticed a few times when we were going up steep hills or if i had to put it on the floor to pass someone that it would spark knock, bad too. Never had an issue with this before. I put 93 in it and the problem went away, filled the next tank with 87 and it came back, filled again with 89 and haven't noticed anything yet, although i was only 40 miles from home at that point. 92k on the 4.0 OHV, timing chain has never been replaced, just did plugs and wires a few months ago. I'm not sure what would be causing this or how concerned i should be with it... any comments?

 

[dalefanatic38]

you got to use premium gas. i have the same truck with 103,000 miles. if i run 87 it knocks and throws a lean bank 1 and 2 code. i put 89 in it and have had no problems.