1996 Jeep Cherokee exhaust smells rich.

base0608

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Hello all. I have a 96 Jeep 4.0L with 164k miles. It runs really well, but the exhaust smells like it is running rich. It sort of smells like what older cars did when they were flooding out. But it never feels that way. It idles great and runs very well out on the road. There are NO codes either. I am sure the Jeep could use a tune-up, but I wouldn't think that would cause the exhaust to smell so strong. Does anyone have any ideas of what I could do to correct this?
 

kev2

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hopefully everything is stock?
no add on's , aftermarket accessories...
engine reaches operating temp @200*F ?
gas milage change?
NO codes....did you check or assume? The CEL does it self test during start?

If nothing above applies ...I would ...filters ...plugs (NGK)- secondary ign.
 

base0608

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Yep, everything is stock. No add on's at all. I checked for codes with my scan guage. It came up with NO codes and the check engine light does work. The engine does reach normal temp. I was thinking about replacing the plugs, wires, filters, and what about the O2 sensor? I have heard that the front o2 sensor can get slow and send the wrong info to the computer about fuel mixture, but not trigger a code. Is this true?
 

kev2

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two trains of thought on that 02 idea.
1) if it ain't broke....
2) nothing lasts forever

they get what is called lazy...
do the routine as mentioned, then price a good sensor- NOT a generic you wire it to fit type ... while doing the first idea (plugs etc) spray the sensor with PB Blaster, penetrating oil.....
if you do not see an improvement then procede with 02 if you want...

PS: this is an long lived engine BUT it is old world design...
 

base0608

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Thanks so much for the info. I just don't understand why it smells so strong like raw fuel and the Cat isn't catching it. I thought the cat was supposed to turn it into that rotten egg smell..Kind of strange to me.

Anway, what brand of o2 sensors would you suggest?

Other than the things we have already discussed, is there anything else you can think of that would cause a rich mixture without setting a code?

Thanks again.
 

kev2

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engine temp - not getting hot enough, wrong Thermostat -

A bad air filter or K&N (POS) .....

short drives can prevent Cat from doing its work effectively....they want to be HOT

BUT the diagnostics would soom see a problemmm

I am hoping our resident parts man can recommend a national brand 02 I will follow up
 

jay

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Check fuel pressure regulator in fuel rail, pull vac hose and check for leaks.
Look for external leaks in fuel rail.
 
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