Can a bad oxygen sensor cause fouled plugs? - Page 2 -
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Go Back > Models > Jeep Grand Cherokee & Commander Forums > WJ Grand Cherokee Forum > Can a bad oxygen sensor cause fouled plugs?

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Unread 12-19-2013, 01:28 AM   #16
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2003 WJ 
Join Date: Mar 2013
Location: Wrentham, Suffolk UK
Posts: 80
Originally Posted by ShadowTek View Post
So if the purpose of the upstream sensor is to determine the "correct" air/fuel ratio, then the downstream sensor will force a different AFR to get the desired emmisions effect?

What happens if you unplug the downstream sensors? Can the upstream sensors not control the poper AFR without the downstream sensors?

This just seems like needless complexity.
The upstream O2 sensors control the AFR, the downstream ones are only there to detect a faulty cat, if you disconnect them it will throw a code.

The first thing I would do is swap both upstream sensors over to see if the problem moves to the other bank. If it does then your O2 sensor is faulty.

Without proper diagnostic equipment you have to use a process of elimination, not guesswork.

One thing at a time


2003 WJ 2.7 CRD Overland
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Unread 12-19-2013, 05:35 AM   #17
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2004 WJ 
Join Date: Jun 2012
Location: Somewhere, Nowhere
Posts: 50
I'm waiting for a cheap OBD2 scanner that I found on Amazon, so maybe that can tell me something. I've seen the Youtube videos where some scanners can display live voltage readings of the sensors and whatnot, but I don't know if the one I ordered can do all that or not.
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