Gotta question fella's My dad has a 2000 4.2 xlt spark knocks under load or acceleration, I've changed the plugs and it calmed the spark knock down alittle...I'm thinking the timing is off

What do you guy's think?? Any help would be greatly appreciated

 

is it stock? what octane fuel does he use? timing can cause it to have spark knock. what brand gas does he use? could also be running lean.

 

Yea, its bone stock, he's used 87 oct for the most part..Sometimes he uses a higher octane and he said it seems to not do it as bad...I believe he mostly uses Shell

 

Take it to a dealer or shop that can do a Motorvac or BG intake cleaning job. It's probably all carboned up. The other option is keep using high octane gas.