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Old 10-29-2010, 08:46 AM   #1
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HELP!! O2 sensors keep fouling???

HELP!!!!!!!!!! If you are a mechanic or fellow jeep owner (hope you dont have the same problem) my 1997 jeep wrangler (4cyl) keeps fouling o2 sensors. The computer says the engine is running both rich and lean at the same time up and down stream. The Jeep runs rich, horrible gas mileage, smells of unburnt gas and sooty exhaust. It runs better after warmed up and over 2500 rpm ( replaced plugs, o2 sensors two times already, fuel bar, air filter, diconed battery, reset codes) motor is new rebuilt on 20,000 miles. After replacing o2 sensors runs great for 3 days then back to same symptoms and fouled o2 sensors. It runs but ratty. What is causing these o2 sensors to keep fouling???

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Old 10-29-2010, 02:40 PM   #2
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What makes you think they are fouling? Coated with Carbon?

Check for a few things:
Exhaust leak, even a small one lets O2 in, causing the computer to think it's too lean, so it richens it up.
Vacuum leak - intake manifold etc. - again, too much O2.
Plugs/wires etc A misfiring plug lets too much oxygen go out - the computer thinks it's too lean, richens it up. Make double sure your plugs are what the underhood sticker calls out - even if the burger fryer at Autozone says different.

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Old 10-29-2010, 06:03 PM   #3
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x2 on what rrich says. I now they are different animals but had a e150 van in not to long ago and same thing 02 sensors carboned up with rich and lean code-wtf. wound up finding an unmetered air leak-crack in intake tube after maf sensor. just a thought.
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