The truck has been a little sluggish lately and the mileage wasn’t so good, so I I started to consider that the O2 sensors could be tired. 140k on the sensors.
I take a look at the live values using my IID tool. The graphs weren’t responding very quickly does the banks weren’t very matched at all, often far out of sync.
Wanted to go out with the local Rover group on Saturday, so I found 4 Denso sensors, the MAF and the tool, shipped 2 day for under $400.


Fronts (pre cat) were the same part number: Denso 234-9075 Oxygen Sensor $86
Rear driver (post cat) is longer: Denso 234-4266 $46
Rear passenger: Denso 234-4265 Oxygen Sensor $46
MAF: Delphi AF10135 Mass Air Flow Sensor $73
Tool: GearWrench 3925D 3/8" Drive Low Profile Offset Oxygen Sensor Socket 7/8" (22mm) $11

I was able to do all of them in off road height without removing any wheels or heat shields, but it’s tight and you have to get creative with the openings you use for your arms. Front drive shaft is really in the way for the front driver’s side sensor. I almost gave up on it. Took a total of 2 hr using just a couple of tools.
I found it very difficult to disconnect the O2 sensor connections. It is much easier if you slide the connectors towards the front to get the sensor off of the plastic clip, then you can pull the wires down lower.
Driver’s rear runs under a metal bracket, I was able to remove one 8mm bolt and bend the cover up enough to remove the wires.

MAF takes 2 minutes to change. T25 screws I believe.

I cleared the adaptations with the Gap Diagnostics IIDTool.

Test Drive shows very noticeable improvement in off the line acceleration. The graphs looked better and the Fuel trims were around 0-2%

So, overall happy I did it!

 

Just FYI, the rear sensors never have to be replaced unless they are reporting an issue with the convertors. All the downstream ones do it monitor the cats to make sure they are working. They have zero effect on the economy end of things. And being post-cat, they generally hold up a lot longer.

 

Good point! Probably should have left them in. I tend to throw money at the Rover! I must like it or something

I noticed that Atlantic British sells a set of four. Is that a marketing thing or do the Rover sensor need changing more than others?

 

Im not sure the interval set by Rover. They are not listed on my sheets, just belts, etc. But generally 100k is the limit. So if using stock spark plugs for the V8, the best time is to replace O2 sensors is when the plugs get replaced. With that said, I like to replaced O2 sensors at around 80k miles. But really, thats a LOT of miles anyway and the odds of most people changing them more once while owning a vehicle is not terribly common unless you plan to keep the vehicle for many years. With O2 sensors and spark plugs, it can not hurt to change them a little early. But waiting can be bad.

 

Strange, here is the part number I have for the passenger side rear. Fit fine and has been trouble free. Maybe a difference between years?

DENSO2344264

Edit: Ahh yup, looks like only 2005-2006 use 2344266. 2007-2009 use 2344264. The difference is a length of the wire for the plug.

I also wonder: which had a bigger impact, the new O2 sensors or new MAF?

 

I had cleaned the MAF the day before and didn’t notice any difference.
I’m a little disappointed though. The extra pep is gone again I wonder if the computer has adjusted for fuel or some other sensor. I got under there yesterday to make sure none had loosened. All seemed tight, at least I couldn’t tighten any more. The equivalence ratios are changing rapidly and very near 1.0.
Mileage was good on a trip Saturday.

I wanted to pull a spark plug...those buggers are tight and hard to get to! Read about a lot people have difficulty removing these plugs....