For the last week, my 94 740IL has been making a rattling/clanging noise
under the passenger seat, especially when accelerating from a stop up to
around 40 mph. I got under the car this weekend and couldn't find anything
out of the ordinary. Called the dealership this morning, and from my
description they said it sounded like one or both of the catalytic
converters were going bad. They then quoted a price of around $1,300 to
repair (not sure if that is for one or both). Is it safe for me to drive it
for the next week (until I can take it in to the shop)? What are the
environmental regulations in the US regarding the converter and emissions
It is difficult to tell for sure, but odds are that there is trouble with a
heat shield or two. It is entirely possible that the trouble is external to
the CAT(s), which means you can possibly secure the heat shield with a hose
clamp, or perhaps locate an empty screw hole and fill it with the
The price quoted is most likely for one. You can get a CAT from other
sources much cheaper than the dealer sells them for.
While smog rules require you to have a CAT, nobody is likely to notice until
it comes time to renew the Registration AND a Smog Check is due at the same
It's a common problem on early e38 740s that the cat breaks up inside
and rattles. Mine occasionally rattles but so far hasn't affected
performance. You can get aftermarket cats for something like $350 but
you may have stricter controls in some states.
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