Replacing O2/Lambda sensors

[svvg]

Hi - am new to the forum but a regular on other bmw sites.

Just picked up a 2004 4.8 (N62) E53 X5. It has 103,000 miles and the original O2 sensors. Car runs fine and no codes logged on INPA or DIS, but these are "supposed" to be changed at this mileage...

Is it worth doing... (anyone have any experience of the difference in the absence of a failed component?) as cost is just shy of £400 for the Bosch sensors... Assume the new sensors might improve fuel consumption a bit - but grateful for any experiences on this before I shell out on them. Already have a parts bin of £1800 (all anticipated in the purchase) as giving it a full refresh... and swapping some perished rear bushes and links - and brakes - plus all fluids etc...

Thanks for input...!

[bcredliner]

Since it's running fine and their are no codes I suggest working on other stuff that is obviously in need of repair or replacement.

[svvg]

Ok...doesn't really answer the question though - have you replaced lambda sensors in the absence of error codes, and seen a benefit? While they have 't failed, I'd asume they're like many electrical components which can suffer from reduced performance without necessarily triggering a noticeable issue - especially when it happens over a large period of time - eg dirty mafs, old coil packs etc. Might not cause the car to drive badly - but may hinder full potential, or affect fuel economy compared to another car with new O2 sensors.

Interested to hear whether anyone's changed the parts as per bmw and bosch recommended interval and seen a benefit.

Many thanks!

[StephenVA]

Any replacement that removes a part that is slow to respond to changes in the air/fuel ratio that is NOT throwing codes (which means it is NOT responding to any changes) will provide better fuel economy results and better driveability feeling to the car. Kinda like a new accelerator pump and a clean carb provided back before O2 feedback sensors and fuel injection. This plus the TPS are the sensors that tell the engine management system that you have pushed on the accelerator (1%-100%) seeking a response from the engine. i.e. MORE POWER!

Now the question is for you. Do you even notice small increases in changes while driving? The average knuckle head driver, the answer is no. Parts could fall off the suspension before anyone notices. Noise? What noise? Hopefully you are in the rare camp that cares and notices as that is why you are here on the forum. Welcome

Bottom Line: Yes replace them and as Danny mentioned, add them to your list of repairs/upgrades, then rank them on the scale that matters to you the owner. Does it start, stop, and safe? THEN LIST EVERYTHING ELSE.

Helpfull?

[svvg]

Thanks for helpful response - seen a few of your threads on spark plugs(!) - am pretty sensitive (and a delicate flower.... ;-) ) - have a few track cars and do feel the difference between components (new coil packs make a difference, worn bushes etc) - but never had a car with this type of mileage "from-the-off" - where any "deterioration" would have been very gradual - and having done maybe £300 miles in the car - it feels good - but not sure "how" good it was supposed to be.

OCD will prevail I think. Will run through the car over a couple of weekends.

Thanks for responses.

[AV8R4AA]

I try to replace my precat Oxygen Sensors around 100K miles.
The post cat O2 sensors aren't as critical.
I replace mine even if they don't throw a code.

[upallnight]

You can use diagnostic software to see how the 02 sensors are working. If the voltages are varying up and down they are fine. If there is a lag when the engine is rev, you probably need to change them.

[oldskewel]

My OCD got the better of me not long after I got my 3.0i. So I replaced the original front O2 sensors at around 170k miles, hoping for better MPG. No codes or engine issues before the change ...

And afterwards, no change at all in MPG, idling, accelerating, even imagined improvements. Nothing! I was hoping for at least some placebo effect on this one.

So I'd vote to leave them in there until you get a code or some measurements that suggest there is a problem.

[bcredliner]

I replaced 02 sensors at 60,000 miles on my x5 because of mods I have done. I will replace the sensors on my wife's 335 at 100,000 miles if we keep it that long. When I have changed them on other BMWs we've had in the past at around 100,000 miles the butt dyno said performance improved but I was never sure. Seemed like mileage was a little better but based on mix of city/highway driving I can't say for sure either.

My response was based on your concern about the cost. Just suggesting you still have the option to save the money since there is no indication they are failing.

Obvious, there can be performance deterioration of 02 sensors without a code or check engine light. And yes, it is recommended to replace sensors after 100,000 miles. That doesn't mean at 100,000 miles they drop dead. Might consider checking them to see if the voltage is per spec. You could also have an emission test done to see if engine is in compliance. Sometimes the exhaust pipes are sooty indicating a rich condition if engine isn't burning oil.

It is reasonable to assume but not expect you will get some improvement if only mileage. If you replace the sensors I would consider replacing spark plugs, fuel and air filters and at least cleaning the MAF if they haven't been addressed .

[svvg]

Thanks for the above guys. Cleaned the maf and changed plugs, oil, air and fuel filters. Hadn't thought about looking at the live-feed read-outs on INPA - will give that a whirl. Car drives really nicely - but fuel consumption doesn't seem to improve from 13mpg (I know it's a thirsty beast - and it's not a shock as such - but it never seems to get above 13mpg even when driving very sensibly - so might be over fuelling a bit). Helpful advice from everyone - so thanks. Will check some live feed on INPA and see how it is.