I just got a 1997 Grand Cherokee Laredo 4.0 6cyl, the previous owner said it was stucked for almost 4 months on his garage. The first thing I noticed when I start the engine is that the the fumes coming out on the exhaust has a fouly smell in to it, smells like rotten fuel. So I took it to the shop for some suspension and engine maintenance, change all the filters, oil and fluids. The head mechanic told me he already adjusted the oxygen sensor and told me to take it out for a long ride on the expressway for the cats to release the stucked carbons. I'll took it out tomorrow and see if it will do improve. Just in case it will not, what are things I should look in to or probably need to replace? Any info will be great, thanks.

 

How does a mechanic "adjust" an oxygen sensor?

The rotten egg smell is typically caused by the converter. It usually happens when you install a new converter. Give it about two weeks and it should go away. The smell is more of an annoyance and does not hurt anything, as long as you do not have any check engine lights coming up you should be fine.

 

A rotten egg smell is an indicator of unburned hydrocarbons going through the catalytic converter. There is no adjustment on an O2 sensor.

 

Ok, I see. So what could be done with the unburned hydrocarbons? Thanks.

 

Uhhhh, ensure that your engine burns them.

It could be as easy as bad fuel, and you need to use it up. Or it could be that your PCM is fooled into running rich.

 

Unburned fuel is caused by misfires, too much fuel entering the combustion chamber, or not enough air entering the intake manifold. All you can do to insure all of the fuel gets burned is to keep the ignition system in good shape, make sure you have good compression, make sure there are no vacuum leaks, make sure the air filter is clean, and make sure all of the engine management sensors are functioning.

 

I just got home after taking my Jeep into a long drive, I only got up to 100km/h, Philippines road is pretty much clogged up. I noticed when I turn off the A/C the engine is more responsive, although I could smell the fumes inside (windows open), I can't stand the smell of it, it's spoiled fuel, yuck!. The K/N filters is clean, no check engine light. I guess I need to take it to another shop and have it diagnosed properly. I'll take note of your advice Bustedback, thanks.

 

I did not know that there is an exclusive all Chrysler shop near our house just 500m away. After some testing on their scanner- Oxygen Sensor, after 15min, new O2 Sensor, and all is good Goodbye rotten smell and black smoke. Now it's time for some exterior/interior deatiling and new wheels