Oxygen sensor; replaced, now runs rough & "check engine" | Ford Explorer Forums - Serious Explorations

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Oxygen sensor; replaced, now runs rough & "check engine"


December 9, 2013
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City, State
Los Angeles, CA
Year, Model & Trim Level
1992 Ford Explorer XLT
Took my 1992 Ford Explorer XLT (4-door, auto 4WD, auto tran, 4.0 V6) for smog test (California) and it failed. It seemed to run fine, and indeed everything passed EXCEPT "NO (PPM)" -- Max 699, measured 2342! So, it's a "GROSS POLLUTER." (I now suspect this was caused by an unoticed missing 8" "intermediate" pipe in the exhaust system.)

I'm over a barrel (very broke, NEED to get the Ford running and licensed), so the tech suggested it probably is a bad Oxygen Sensor (the primary one, before the catalytic converter). I coughed up the $50 for a new one and replaced it.

After replacement, as always, the Ford ran fine ... until about 15 minutes later, while driving. Suddenly, a clunk, power drops, engine runs rough and smells of fuel, and the "check engine" light comes on. I nursed it home.

The next morning, I try the Ford again. It starts, runs okay, then after about 15 minutes of idling, the same bad thing happens: sudden clunk, power loss, rough running, fuel smell, 'check engine' light.

I then re-installed the original oxygen sensor, hoping to solve the problem.

Now the same problem, after another day: it starts, runs, then after a few minutes, loses power, check engine light comes on, it chugs and knocks.

Summary: I put in a new O2 sensor, and this problem began. I removed the new O2 sensor and put the original one back in, and the problem continues. BEFORE I changed any O2 sensor, the vehicle ran good and was reliable.

Anyone have any idea what I probably did wrong, and how to fix it? Could it have something to do with the computer not recognizing the sensor?

Yes, the tail pipe connected to the cat would be an issue. How's your fuel filter? Fuel pressure