it was still popping after you replaced the plugs? did you ever check the timing? i know its not adjustable but the oil pump/cam sensor may not have been put back in time when he put the timing belt off. and i know ive been harping on this but have you put freon back in it?

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2000 ranger 2wd 3.5" Fabtech lift, 31"x10.5" BFG all terrains, leather bucket seats, poweraid TBS, k&n, flowmaster, 2.5L... but soon to be 302