Question for the Auto Mechanics, Rotten Egg Smell *REVISITED* Pg 5

clogged cat homie!

clogged cat can be caused by faulty bank 1 o2 sensor giving false reading causing the computer to think its running lean and dumping extra fuel. or it could be caused by either a faulty thermostat or coolant temperature sensor, which would cause the computer to do the same thing. or if its a car that utilizes a secondary air pump for emissions, a faulty solenoid would cause the vehicle to run rich, causing cat to become clogged. clogged cat can easily be checked by using a infrared temp gun to measure the temps at the front and rear of cat. if the temps are close to the same its not clogged, but if the engine side is significantly higher....bingo!

but rotten egg smell generally points to a clogged cat.
you will also notice a decrease in power, especially under load or going up steep hills. vehicle will seem to "bog" down

Problem-rotten egg smell
rotten egg smell generally points to clogged cat
Clogged cat generally caused by a rich fuel mixture condition
running rich generally caused a failure in any of sensors related to the fuel/emissions

bank 1 & 2 o2 sensors
map or maf sensor
IAT or coolant temp sensor
secondary air system
egr system

a sticking open secondary air solenoid or egr valve can cause a engine to run rich without throwing a DTC by allowing unmetered air into the exhaust system, causing bank 1 to detect a lean fuel mixture and adding fuel to compensate resulting in a unnecessary rich fuel mixture condition.

The car is an 01 Grand Prix GTP modded.

Its not clogged, but thats not to say it will not get that way. It has plenty of power, it still turns the wheels over at 40 mph if I put the pedal down just like it did when I originally installed the mods.

It does not always have the smell. I tend to baby it around town and if I get in it a little bit it starts. As was mentioned in an earlier post about running it harder seems to help, if I get on the highway for 40 miles or so it stops for a few weeks. Changing where I get gas also makes it stop for awhile. Running it harder does indeed seem to make it go away, for awhile. When I am out tomorrow I will run the dog shit out of it and see what happens.

According to the computer, everything is still functioning fine, no fault codes. My real time OBDII software(torque pro) shows the temp as 180 degrees as it should be with a 180 degree thermostat. Short of actually doing manual checks with voltmeters and such, I am assuming the computer would alert me if something was running out of spec.

Running rich I suppose could be a possibility here if unmetered air is getting in, I will check into it.

if bank 1 is detecting a false lean condition due to unmetered air, you'll see a big fluctuation in the reading on bank1o2 in freeze frame diagnostics. and was your pcm tune a mail order or real time tune?

if bank 1 is detecting a false lean condition due to unmetered air, you'll see a big fluctuation in the reading on bank1o2 in freeze frame diagnostics. and was your pcm tune a mail order or real time tune?

*** you can also do a basic check if you have a good dtc reader. if your fuel trim is running greater than 10%, the computer is trying to compensate for something. one thing to remember here is that your car is supercharged. its better to run lean with boost than rich, so be careful running it hard until you get it straightened out. running rich with a boosted car opens up the opportunity for detonation...which is something you want to avoid like the plague.

could be the battery. I know when batteries go bad or leak they smell like rotten eggs.

Always better to run rich no matter how it's boosted. Rich will give you some margin of safety. Lean will cause detonation / preignition issues. Lean is hot. Two strokes will seize if they go lean under (heavy) load / throttle.

Now, diesels on the other hand....

if bank 1 is detecting a false lean condition due to unmetered air, you'll see a big fluctuation in the reading on bank1o2 in freeze frame diagnostics. and was your pcm tune a mail order or real time tune?

*** you can also do a basic check if you have a good dtc reader. if your fuel trim is running greater than 10%, the computer is trying to compensate for something. one thing to remember here is that your car is supercharged. its better to run lean with boost than rich, so be careful running it hard until you get it straightened out. running rich with a boosted car opens up the opportunity for detonation...which is something you want to avoid like the plague.

The car is an 01 Grand Prix GTP modded.

Its not clogged, but thats not to say it will not get that way. It has plenty of power, it still turns the wheels over at 40 mph if I put the pedal down just like it did when I originally installed the mods.

It does not always have the smell. I tend to baby it around town and if I get in it a little bit it starts. As was mentioned in an earlier post about running it harder seems to help, if I get on the highway for 40 miles or so it stops for a few weeks. Changing where I get gas also makes it stop for awhile. Running it harder does indeed seem to make it go away, for awhile. When I am out tomorrow I will run the dog shit out of it and see what happens.

According to the computer, everything is still functioning fine, no fault codes. My real time OBDII software(torque pro) shows the temp as 180 degrees as it should be with a 180 degree thermostat. Short of actually doing manual checks with voltmeters and such, I am assuming the computer would alert me if something was running out of spec.

Running rich I suppose could be a possibility here if unmetered air is getting in, I will check into it.

if bank 1 is detecting a false lean condition due to unmetered air, you'll see a big fluctuation in the reading on bank1o2 in freeze frame diagnostics. and was your pcm tune a mail order or real time tune?

*** you can also do a basic check if you have a good dtc reader. if your fuel trim is running greater than 10%, the computer is trying to compensate for something. one thing to remember here is that your car is supercharged. its better to run lean with boost than rich, so be careful running it hard until you get it straightened out. running rich with a boosted car opens up the opportunity for detonation...which is something you want to avoid like the plague.

Always better to run rich no matter how it's boosted. Rich will give you some margin of safety. Lean will cause detonation / preignition issues. Lean is hot. Two strokes will seize if they go lean under (heavy) load / throttle.

Now, diesels on the other hand....

not necessarily true with boost. N/A motors yes. with boost lean conditions rarely open up the chance of pre-ignition due to charge air being cooled prior to entering the plenum, lowering the IAT, and effectively having a cooling effect on the pistons. with boost (especially turbo) running rich to compensate for increased boost can cause detonation if proper compression ratios are not maintained I.E changing your stock supercharger pulley to create more boost, without changing the compression ratio to compensate for the increased pressure, changing the original Knock resistance characteristics.

a rotting battery will also smell of sulfer. being overcharged.

I respectfully disagree. Lean is what is going to smoke a piston. Rich is going to have a cooling effect.

Now, if you are referring to going way lean from stoich, and getting a "cooling" effect from that I may agree with you. But you are only fooling yourself with that. Increasing boost (to increase power / BMEP) and then having to run lean to prevent full heat is a crutch to justify the boost number. You should be able to achieve slightly richer than stoich (say, 12.5:1) at a given CR and boost number. In other words, you should not be running lean to justify CR and Boost numbers. This is not how you achieve maximum Brake Mean Effective Pressure.

:0nmyt0es: