Fuel/Egg odor at idle

[Xdt]

Guys, when I start my car it’s very rich at idle and has a strong egg smell. The odor will make your eyes water, if that gives you an idea of how strong the odor.

The car is a 1990 124k miles, original exhaust, with the only mod being new injectors, new plugs, new pcv valves. The car runs strong in power mode, does not bog, however under acceleration someone informed me of a little puff of smoke and the smell of fuel as I passed. Also, there are no codes displayed. This has been verified with tech 1.

My apologies for the lack of details, however as of now this is what I know.
Any ideas of what to check?

Thank you

[BigJohn]

Catalytic converter's?

[WARP TEN]

O2 sensors? --Bob

[Hog]

If the car is babied a lot, it might be time for an "Italian Tune-Up".


Procedure:
1) Warm up car by driving for 10 minutes
2) In a safe area, I prefer freeways, perform some aggressive whatever rpm to redline pulls. Get them cats a cooking.
3) Allow a cooldown period by driving more gently for a few minutes.
4) Park car.


*Some members say that the LT5 will respond even more favourably if you yell "Momma Mia!" during and immediately after performing Step#2.


You are smelling the Hydrogen Sulphide which smells like rotten eggs.
Sometimes a change in gasoline brand can help, some gasolines have more or less sulphur contents.
It does take a while for these catalytics of a 3-way Catalytic(TWC) to reach the light-off temperatures required to convert
1)oxides of nitrogen(NOX) to Oxygen(O2) and Nitrogen(N2),
2)Oxidation of Carbon Monoxide(CO) to Carbon Dioxide(CO2)
3) the Oxidation of unburned Hydrocarbons(HC) into Carbon Dioxide and Water(H2O)
which only occurs after the cat has reached a temperature of 800ºF. Which is why its advantageous to place the cats as close to the heat source(engine) as possible.
I have found many early 1990's GM cars/trucks(OBD-1) to have this issue.
While the cat is operating during its low temp cycle, it is absorbing sulphur, then after light off, when the catalytic is operating in its high temperature cycle, all that sulphur then combines with hydrocarbons to for Hydrogen Sulphide(H2S).
Nickle and/or Manganese is added to the washcoat of a catalytics substrate in order to block the "collection" of sulphur during the cats low temperature cycle, but after a while, these elements lose their ability to block the uptake of Sulphur.


Yet another reason to start your car and begin to drive, your not doing the car any favours by "letting it warm up" at idle. The quicker you get the cars systems to their operating temps the better, within sane reason of course.


There are certain conditions which are harmful to catalytic converters, they can get contaminated(poisoned) by lead and antiseize products etc
and/or they can be damaged by certain condition such as: excessively rich or lean air/fuel ratios.


Some new Oxygen sensors cant hurt, esp. if they are older, or if some sort of homemade extensions have been used for the O2 sensor wiring. I suggest GM/Delco only, avoid Bosch for narrowband oxygen sensors.(though Bosch wideband O2 sensors seem to be OK).


Some of these cats will be going on 30 years old, they are bound to begin to show their age.


I just noticed that if you go to Rock Auto and plug in the certain years of LT5 powered Corvette, there are various options for catalytics depending on age. But when I selected a 1995 ZR-1 LT5 DOHC that you get a service where you send in your old cat and they re-manufacture your cats. I thought that may help some of you.

[Xdt]

All, thank for the replies. I forgot to mention that I installed new 02 sensors earlier this year. I will perform the Italian tune up, but as stated I was told of the rich smell and puff of smoke during one of my “hey watch this” moments. As stated it’s possible the converters are showing their age. The smoke could be pcv related, has anyone found a good replacement for the driver side pcv?

[Hog]

I gave seen a few dyno runs where it appears that there is a "puff" of smoke during the WOT run.
The 1990s also don't have valve seals like the 91-95s do. Perhaps there's a lot of oil in the top end during a higher rpm run? Not sure. Smoke coming down from high rpm is certainly indicative of oil being "sucked" into the chamber.


It would be nice to strap her down on a dyno and see exactly what is happening during a WOT run.


Some spurts of smoke while at WOT under power, and lots when throttle is closed and intake is pulling lots of vacuum.
This is the first video I found and illustrates what I'm talking about.
http://www.youtube.com/watch?v=drbFmqJIMMU

[Xdt]

Paul,
I believe I will take your advice on the dyno pull.
Thanks again

[biggiefl]

Egg smell usually means cats but try the other stuff first.

[32valvesftw]

Mixture is off, prolly due to a bad sensor somewhere if you have no codes then maybe your cats need replacing.

[Top Toy]

Puffs of smoke during WOT acceleration are sometimes indicative of your knock sensor temporarily pulling timing. Are you running a stock chip?

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