limpy imp

i tore down motor today and still can't see any problems so i'm going to change out lifters and see if that fixes it.

is there a way to isolate the effected cylinder/s by grounding spark plug and listening to engine.

i found out the hard way that 04 impala had run out of oil. now engine is rattling/tapping and i'm not sure if its time to replace engine or replace lifters.any help would be greatly appreciated