crappy gas mileage

[Unregistered]

Does anyone know what would cause the car to run rough with extremely bad gas mileage (10mpg) other than the oxygen sensor? I reugularly catch a whiff of an odor that smells like rotten eggs. Brought it to the guy who sold me the car and who services it regularly and he hooked it up to the computer which couldn't narrow down the problem. I've tried the stomp test and can't get it to work. Any thoughts would be greatly appretiated.
Thanks...Jeff

1994 525i
100,000 miles
stock

[KenB]

Rotten eggs is usually a sign of a bad cat. Check to see if one died under your hood.

Seriously, the catalytic converter is probably bad.

Any reinforcements???

[tim s]

Rotten eggs is usually a sign of a bad cat. Check to see if one died under your hood.

Seriously, the catalytic converter is probably bad.

Any reinforcements???

[Tiger]

Cat is not at fault...geez... it can only help so much with excess fuel... Just take the car into dealer and have them fix it... There are alot of things to check... Start by checking with Bruno's website... bmwe34.net

[BigD]

I also don't see what the cat would have to do with it (not sure why "geez" but ok). A bad cat would make your emissions horrible. But fuel economy? Besides, the O2 sensor should be shot as well, if the cat is. THAT would cause the crappy fuel economy...but his computer should have picked that up. And if it's that bad, so would the stomp test. Do you have a check engine light? The stomp test just requires you to be quick. Once you turn your ignition on, press your gas pedal down all the way and all the way up 5 times with a constant rhythm. Just make sure it's coming all the way up and all the way down, and that you're under 5 seconds.

Cat is not at fault...geez... it can only help so much with excess fuel... Just take the car into dealer and have them fix it... There are alot of things to check... Start by checking with Bruno's website... bmwe34.net

[632 Regal]

Made it easier on my foot when I was checking things a while back.

[BigD]

That's true actually, now that I think about it. All the DME cares about is having the WOT switch triggered, not the idle.

Made it easier on my foot when I was checking things a while back.

[ilya]

as far as the Cat goes..
from what i learned, different types of gas might cause that smell. i have that same thing with my car. it used to happen a lot, but now that i haven't filled up from that station in a long time, that smell appears maybe once a month.

from what i heard and learned, if you get that smell, simply go to a different gas station next time..

[dave b]

I'm staring at a BMWNA service bulletin dated september, 1996 regarding "hydrogen sulfide odor from the exhaust system"

To summarize: H2S, which is what smells like a rotten egg, is a by-product of the cataytic action. SO2 is formed in the catalytic converter and subsequently attaches to the so-called promoters during constant speed driving with an ideal or slightly lean air/fuel ratio (your O2 sensor does this). Under acceleration or in rich condition, SO2 is reduced to H2S and released through the tail pipe. This stinks. The amount of H2S released depends on the sulfur content of the fuel.

Their recommendation: if their are no faults in the DME, choose a different name brand fuel, as the sulfur content of different fuels can vary greatly.

BMWNA will no cover the replacement of the cat for this complaint under warranty.

Hope that helps - why are you so sure it's not the O2 sensor?

[winfred]

certain mixture conditions will make the cat overheat and produce hydrogen sulfide instead of hydrogen and oxygen, if nothing else rotten eggs suggests the cat is working