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Hog · 10-31-2017

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.

10-31-2017	#4
Hog Join Date: Jul 2010 Location: Woodstock, Ontario, Canada Posts: 1,271	Re: Fuel/Egg odor at idle 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.