Hello everyone, looking for some info on the lr3 o2 sensor positioning. Recently purchased a 2006 LR3 with the 4.0 v6. I now know that these are somewhat rare and not well liked. Please bear with the long post. When we first looked at the LR3, the owner told us that it had a rich or lean code on bank 1, he couldn't remember which. They replaced the upstream o2 sensor on bank 1 and took it to a shop to clear the codes, also to get a tune up done. They got new plugs and wires, belt, oil change and some other stuff done. The shop told him that he also needed new coil packs for cylinder 1,3, and 5 since it was misfiring. The misfire was a new problem and after a couple months and a lot of money the owner gave up and decided to sell it. I mistakenly assumed a vacuum leak to be the cause after checking the codes and seeing a lean code and rich code simultaneously for bank 1, misfire on cylinders 1,3, and 5, an occasional misfire cylinder 2, random misfire and misfire on startup; bank 1 fuel trim was at -23.3% at idle. We found a exhaust leak where the manifold bolts to the cat, fixed that which cleared the rich and lean codes. Still had the misfires, started looking in other areas such as sticking valves, clogged injectors, poor quality coil packs; everything checked out. After pulling the valve covers we saw that the rear timing chain guide was broken, so we pulled the engine and replaced it. After getting the engine back in, all of the noises were gone but the misfire codes were still there with cylinder 2 being constant instead of intermittent. We then pulled the spark plugs to do a compression test in case we had the timing slightly off. All cylinders were around 190 psi. Put the plugs back in, they stayed on the same side of the engine but not necessarily the same spot; we didn't mark them.
Ran injector cleaner directly through the rail, still had misfires on 1,3, and 5 with 4 instead of 2 misfiring and the same fuel trim on bank 1. At this point we determined that the problem was likely with spark, fuel delivery, or fuel/ air monitoring and commands. When we reinstalled the engine we put the belt back the same way we took it off, it was wrong. Taking that into account, we swapped the upstream o2 sensors and the misfire codes along with the -23.2% fuel trim followed over to the bank 2 side.

This is a long way of asking about the o2 sensors, every vehicle I've worked on has narrow band upstream for fuel/ air monitoring and wide band downstream for emissions. Rock auto shows wide band being upstream and narrow downstream. What I suspect is that originally the wide band upstream sensor was swapped for a narrow band which induced the misfires to begin with and damaged some spark plugs, they look pretty bad for only being a couple months old. Can anyone confirm the wide and narrow band positions? Thank you for any help.

 

I see that there a number of views but no replies. For anyone wondering, the O2 sensors are indeed backwards with the upstream being wide stream and downstream being narrow. Not knowing this may make me look dumb but I hope it helps someone else. I'll follow up tomorrow when the new O2 sensor shows up and we get it replaced.