The "Rotten Egg" Smell.

When I run my 92 (B12) Sentra hard for a bit, I will begin to smell that "rotten egg" smell. I am assuming that this is because of incomplete combustion, or some sort of valve problem? I had a mechanic tell me that it was probably a plugged Cat Converter, but I had the pipes off recently and it looks pretty good in there (Original converter on it still.)

I am not looking to put alot of money into the car (its just a beater for commuting), but I dont want to see it die either.

Comments?

Does it idle rough after it warms up?

The egg smell is Hydrogen Sulphide (H2S04 from memory). This is a by-product of the catalytic converter and maybe due to a high sulphur content in the fuel you are using. H2SO4 can be toxic but tends to be heavier than air - when you go to a geothermal area you will find the same smell (it's the same substance).

Evidently, Hydrogen Sulphide is preferably to sulphur dioxide S02 which is a contributer to acid rain.

As for the catalyst itself, the catalyst can be damaged by drawing unburnt fuel (eg from persistent misfires) or contamination of the catalyst elements (eg from using leaded fuel) which may not be apparent from a visual inspection.

I'm presuming that you are required to operate a catalyst in your jurisdiction (for some bizarre reason cars in NZ are sold with them but there currently isn't a law preventing their removal) so you may want to see if you can find another cat from a wrecker - I wouldn't pay too much as there is no guarantee the thing will work any better.

Depending on whether your area has tailpipe emissions tests you may have to replace the cat anyway - either that or if you concerned for the environment you may choose to do it anyway.

Originally posted by HuMMerMan
When I run my 92 (B12) Sentra hard for a bit, I will begin to smell that "rotten egg" smell. I am assuming that this is because of incomplete combustion, or some sort of valve problem? I had a mechanic tell me that it was probably a plugged Cat Converter, but I had the pipes off recently and it looks pretty good in there (Original converter on it still.)

I am not looking to put alot of money into the car (its just a beater for commuting), but I dont want to see it die either.

Comments?
Is the engine running hot? coolant level may be too low?
Check the engine's vacuum lines and fittings for leaks. Check engine compression. Check for broken fittings and mounts.
There may be a problem with the computerized engine and emission control systems. (do ems diog.) Check out, injection and emission control systems.
Could be a bad fuel pressure regulator as well.
Any ignition problems?
bad gas milage?

any more symptoms?

oh yea could be the cat. as well. Check for blockage/ restrictions. Might be plugged up.

Not to sound too simplistic but maybe you're pushing your clutch too much. A burned clutch will smell exactly like rotten egs. Exaust problems have more of a sharp smell in my experience.

To answer some things:

1. There are no emissions testing in my area. (Dont ask me why)
2. Car Idles fine.
3. Engine Temp is OK, Fan Operates Correctly
4. Coolent OK
5. Gas Milage is GREAT! Averaging about 42mpg
6. No Ignition problems to speak of

7. Car has VERY little computer equip on it, something could be wrong with emissions control I guess.

8. Some Vacume lines are in bad shape, and probably should be replaced.


I might go to the wrecker and see if I can get another cat (cheap) on the weekend.

Originally posted by Neutrino
Not to sound too simplistic but maybe you're pushing your clutch too much. A burned clutch will smell exactly like rotten egs. Exaust problems have more of a sharp smell in my experience.

I thought about this too, but it happens even if you just run it at high-speeds on the highway for a while, and not even using the clutch. So I kinda ruled it out. Also, not to blow my own horn, but I am fairly proficient with a stick shift, and doubt that I am burning the clutch.

Thanks for all the help :)

The logical thing to me would be to check the cat.

Once when I had a "rotten egg" smell I discovered it was from my battery cooking. A cell had gone bad and so it was only giving about 10 volts of resistance and so the alternator was frying it. When I replaced the battery, the smell went away.
Hope you find the problem.

Prospector48