Recently I changed the oxygen sensor(late August)on my 86 300E , almost immediately noticed when I decelerate I hear back pressure from the cat. I figure the cat. probably has to be replaced(car has 193k mi. on it and also noticed that the metal is peeling). I don't smell rotten eggs or anything. My question is, once I change the cat. (did I wait to long?) do I now have to again replace the oxygen sensor?

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Richie
1986 300E
tint windows
clear corners
euro headlights
16"chrome lorinsers RS90
soon to be 94/95 taillights

you shouldn't have to
engatwork
'95 E320
'97 Honda CRV

What do you mean back pressure? Do you mean "back firing" or "popping". If it is doing either of these, you probably have an exhaust leak at the o2.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by CMuc:
What do you mean back pressure? Do you mean "back firing" or "popping". If it is doing either of these, you probably have an exhaust leak at the o2.<HR></BLOCKQUOTE>

What I'm getting is a popping sound.It definitely is NOT backfiring..