Hello everyone!

I have a 1998 Explorer XLT, automatic, 4.0 SOHC. I ordered both downstream oxygen sensors from Ebay, because they were half the price the parts store gave me, and I could order Borg Warners on Ebay.

I just got them yesterday, and they aren't the same. The tip of one looks quite a bit larger than the other.

My question is, without me crawling under my truck and removing the old ones and disabling my vehicle, are they supposed to be different sizes? The numbers stamped on them are 385 and the other larger one is 177.

I changed the upstream ones a few months ago, and they were both the same, which is why I ask.

It may be a stupid girl question, haha, but any help would be appreciated. I've always worked on my own vehicles. Thanks!!

 

The wire length of both rear sensors is different, so the part number would be different as well. As far as if the parts you received are the correct ones, that I'm unsure of. Have you tried searching for a fitment guide for whatever brand you received? The part numbers listed don't appear to be complete Borg-Warner / BWD part numbers.

Also, are you wanting to replace the O2 sensors for preventive maintenance, or are you trying to solve a driveability issue?

-Rod

 

I had some driveability issues, it is just running rough and idling rough. Codes read were that 3 cylinders were misfiring, one side running too rich, and one too lean (after we put injector cleaner in it if that makes a difference), and one of the rear O2 sensors were not working. I got under it and they both are the same sensor, they sent me one of the wrong ones. I went ahead and replaced the one I think was giving me the code and reset the codes. Hubby is going to drive it in a bit and see if the check engine light comes back on.
He thought he might have sucked some trash in running the gas too low, so we put injector cleaner in it and already had a fuel filter so we replaced it.
We'll drive it and see whats going on. I'll update shortly.

 

If you are trying to solve a drivability issue, you bought the wrong plugs. Downstream sensors do not affect the mixture or drivability in any way.

You would need to be ordering upstream sensors.

Major drivability issues like what you are describing would not likely be caused by bad O2 sensors anyway. Those types of symptoms are more typical of a massive vacuum leak in the lower plenum or of a low compression situation. Go get your intake smoke checked and compression tested so that you have a good idea where you stand.

One side running rich and the other lean does not indicate an O2 sensor problem. Lean codes are most often aused by vacuum leaks or low fuel pressure. Rich codes are most often caused by high fuel pressure or leaking injectors.

A rich and a lean code can be set on opposite banks when you have a major vacuum leak on one or more intake runners on one side of the engine. This causes the computer to detect a lean condition, so it adds fuel, often to both banks. It then detects that one bank is still lean, and the other bank is now rich. Sometimes a leak in one of the exhuast manifolds can cause a similar problem, though this would be pretty rare.

It sounds to me like you need to determine the health of the engine first, then try to see if you can locate the leaks. Lean codes and rich codes do not indicate faulty O2 sensors, but rather often indicate that the sensors are working correctly and that the problem lies elsewhere.