Running Rich. Oxygen sensor, or more? | Ford Explorer Forums - Serious Explorations

  • Register Today It's free!

Running Rich. Oxygen sensor, or more?


Active Member
May 28, 2006
Reaction score
City, State
Fall River, MA
Year, Model & Trim Level
'97 Explorer Sport
Ok. Here's where I'm at. The truck ('97 Sport SOHC) was throwing a "cat failure" pending code when I bought it a year ago (light not on yet, but we cleared it and forgot about it). Months later, it threw a light for an oxygen sensor (forgot which one, but I bet it's the same as the one below). Clear it, and stored the truck for much of the winter (got another vehicle and forgot all about it). So, last week (after I've had it out of storage for a month or so), it throws a code for bank 2, sensor 1. Not just that, but a misfire in cylinder 6, and a pending misfire in cylinder 5. And a few more codes that looked like jolly ol' fun (don't even remember, but they were Ford-specific, not standard codes).

So I took apart my center console and measured the voltage at the downwind oxygen sensors. At first (engine cold), the left one (bank 1?) was reading ok (steady-ish .45 volts), but the other was reading around .7v. After the thing got fully warm, they both read around .7-.8v., sometimes jumping up to .9 if I revved it and let it settle at idle for a while.

My thought is to replace the sensor in bank 2 sensor 1. But, I'm wondering why both banks are running rich? If it was just bank 2's sensor, that would be the only one running rich, right? Might there likely be something wrong with a component shared by both banks? Why only when warm? Something temp related? I'm going to *try* and test the upstream sensors today. I also have a whole set of plugs and wires to go on, but I don't want to replace those until I'm sure everything else is running good (for fear of my procrastination fouling the plugs). Thanks!fouli

I'm sick of 13MPG highway :(

All 4 sensors are identical? I'm going to replace both upwind ones, because I can not get to the connectors to test. But they cost anywhere from $50-$75 at Autozone.