i know i'm terrible for posting 2 threads about 2 different cars 5 minutes apart, but our 78 volvo 240 also needs some attention. anytime its idling, hot or cold, the exhaust smells very rich. we replaced the o2 sensor with no change in performance, and i don't know what else to look at to work this out. any ideas?

 

Rich as in fuel and eye stinging exhaust fumes?

I got a 79 242....and did the following and took care of the eye stinging rich smell but still a little stinky as my catalytic converter is hollowed out...only the walls have some left.

spark plugs
wires, cap and rotor
O2 Sensor
injector seals
exhaust gaskets
intake gasket
throttle body gasket
fuel filter
fuel pumps (both)
4 ounces of Marvel Mystery Oil to a full tank...my car loved it...definitely lowered the rich smell but had the exhaust of a car that did not have a functioning cat in place...Not stingy any more but just old V8 truck exhaust...might not sound right but I could definitely tell on the smell and gas consumption.

I still got to weld on the new cat on the pipe.

 

in the 3 or 4 years we've had this car, we've done a couple of tune ups on the ignition (plugs, wires, cap, rotor), verified timing, replaced injector seals, o2 sensor, and various other stuff i'm not remembering.
the catalyst has always been an empty shell, but every old truck i've had has also been missing the cat, and none have smelled this rich unless the choke was on or something, and this car smells this rich all the time.

if the MMO really does that much good in your car, i might have to give it a shot