it seems as some info got cut off when I originally posted. it's the 2.6 190e that is knocking. it does it under load and is worse when it's warmed up. it seems worst when the temp outside is 90+. I always use 91 octane chevron. I tried other brands and it was often hard to start even though it was premium octane. My plugs get a weird build up on them if that is any indication..like a black puffy ash. not the standard oily carbon from being too rich. I installed cooler plugs (bosch supers) and it helped a little. both the 190 and the 250 are fuel injected and have not had any work done recently save an a/c compressor. thanks for all the response everyone.
'67 250se coupe
'89 190e 2.6 (gone but I kinda miss it)
'07 BMW x3
'59 0319 diesel Omnibus...the "O"
'64 Lambretta Special 185 hot rod scooter
'66 Lambretta SX200
'59 Lambretta 250 race bike
'70 Lambretta GP200
'77 860gt ducati
'66 ducati monza