Rattling in a 3.0 at 2500(ish) RPM
So I have a friend with a 1996 B3000, at around 180k miles who's engine starts to rattle around 2500 RPM. We've ruled out anything with the belts, accessories, alternator, and fuel injectors; but the question as to what it is still remains. When the truck is started and is idling or under 2500 it sounds just like any other V6, as well as if it hits around 3000-3250, however there is that small band where it rattles as you rev the engine through that 500-750 rpm range. Any thoughts folks?
1997 B2300, Expo buckets and center console, a bit of blue paint, and the dual ignition mod. Just over 80k Miles.