Oxygen sensors

[James NZ]

Hi all,

I was reading an article on the internet and it mentioned ""tired" oxygen sensors that should have been replaced". Which got me to thinking, should I be replacing mine? My vehicle is a 95 V8 Disco 1 with 119000 km's (74000 miles). There is another reason for this question. Some time after buying the vehicle I decided to service/replace everything so that I could start my own service history. Part of that entailed replacing all of the spark plugs. Some time after that I noticed the engine idle wasn't quite as smooth as before. The plugs that went in were Bosch. Cheers, James

[BogMonster]

Has yours even got oxygen sensors? A lot of export models don't at that age and I thought NZ/Oz were one of the ones that didn't.

[Bowie69]

Use NGK (BPR6ES) plugs only, V8s are very picky about them.

[pinhead]

If you have o2 sensors plug it in to a computer and see if they work ok they should be flicking up and down continuously

I wouldn't recommend swapping them if they are ok as me and a friend have had no end of bother with these on disco 2 v8 that we have

Think he has had both sides changed twice in his in 12 month and he is wanting for another now just had 1 in mine but I suspect 1 is faulty again as fuel economy has dropped just got to get it plugged in

[FridgeFreezer]

If they're working, don't prat about with them. They don't really get tired.

Use NGK plugs, V8's are fussy. Others may work, but NGK are the known quantity.

[mayur]

if your v8 is fuel injected it has a lamdba sensor(o2) and most manufactures recommend ( if i remember correctly ) every 60,000 miles but no one ever changes them until they go terribly wrong.

the ECU looks for changes in the lambda, which will normally happen but overtime due to exhaust temp and impure burning clogging them up the variations are less making them less effective,

look at you lambda if it only has one or three wires to it dont worrie about changing it, if it has four it sometimes can make a difference but not normally noticeable as the lambda for emmissions not the smooth running of the engine

[Ally V8]

Same as Boggy says,I cant remeber if Oz/NZ spec cars were even fitted with oxy sensors.Look at the exhaust downpipes,if there is a small round thing bolted into the downpipe on each side with three wires coming out of it then they are the oxy sensors.At 74,000m they should be fine if the engine has been running properly and well cared for.You will soon know if they stop working as the engine will run VERY rich under closed loop conditions.These should be when the engine is up to temp and idling or under cruise/ medium load conditions.The ecu will ignore their outputs under wide throttle openings and on overrun.

The black wire is the sensor output wire and should cycle from 0 - 0.8v and down again on a multimeter about once a second.(When the multimeter is connected to the sensor and a good earth - and running in closed loop conditions.)If it will do that and stay at about 0.8v under wide throttle openings then all is well with the sensor.

Many get changed as a result of lack of understanding or blindly following fault codes,often its an airleak or misfire that prevents them from working.Do you have emissions testing as part of your WOF ?

[Range Rover Blues]

Lambda sensors deterorate with age, fact. Manufacturers advise they are replaced after so many miles in order to ensure the car runs as it was designed to, includiing ecomomy and emissions.

An early sign of failure/deterioration is that they cycle far slower between rich and lean, new ones will constantly change.

The ones on the D1 are probably the same as mine and work differently to most which means most one size fits nothing are no good.

I bought some fuel parts ones from my local factor, having priced up the NTK parts (NGKs trade brand). When I unwrapped them they were NTK parts in plain white boxs with about 15%v off the price, result.

I think it was running better but the gearbox failed very soon after, perhaps as a result of all the raw power I had unleashed with the new MAF and Lambdas

[Ally V8]

Lambda sensors deterorate with age, fact. Manufacturers advise they are replaced after so many miles in order to ensure the car runs as it was designed to, includiing ecomomy and emissions.

An early sign of failure/deterioration is that they cycle far slower between rich and lean, new ones will constantly change.

The ones on the D1 are probably the same as mine and work differently to most which means most one size fits nothing are no good.

I bought some fuel parts ones from my local factor, having priced up the NTK parts (NGKs trade brand). When I unwrapped them they were NTK parts in plain white boxs with about 15%v off the price, result.

I think it was running better but the gearbox failed very soon after, perhaps as a result of all the raw power I had unleashed with the new MAF and Lambdas

Its quite true that oxy sensors age - like the rest of us ! But they will function happily well beyond 150,000m IF the engine has been looked after and no driven with misfires etc.LR also used to say that Cats should be replaced at 96,000m on v8 p38's - wonder how many had that done when you consider the price they were ?

The D1 sensors are 3 wire Titania's,so universal ones will rarely work.The best way to test them is with an oscilliscope - not many garages have these,including main dealers.Hence so many being thrown away when in fact they would do alot more work.

[mayur]

i would like to say that the 3 wire lambda isnt very accurate as it only generates a voltage of 0-5 so not much to bother about

[Bowie69]

huh? the 4-wire ones are only 0-1 volts...... same for 3,2,1 wire stock ones.0-5v ones are considered more accurate, at least they give a better resolution to the scale of AFR.

[Ally V8]

The Titania sensors fitted to 3.5,3.9 and 4.2 Hotwire v8s are 0-0.8v,just because it is s small voltage it does not mean its not important.The critical thing is the 0.4v threshold which the ECU sees as the point at which to alter the injector pulse width to achieve as close to a stoichiometric value of one as possible.As the voltage goes above 0,4v the pulse width will narrow to bring the voltage back down below the 0.4v when it will widen it again.

They are more accurate and give a cleaner waveform than 0-0.8v Zirconia sensors and dont need an external oxygen reference.But even the 5-0v,(Not 0-5v) ones used in later Gems equipped V8's are STILL narrow band in terms of their ability to monitor air fuel ratios.Its not till you get to the later UEGO'S,(Universal exhaust gas oxygen sensors.) that you can really map the actual fuel/air ratio from about 10/1 up to about 18/1.

But saying the output from an upstream narrowband sensor is not important is just not sensible as most ecu's will still try to use info from them even if they are faulty or disconnected.

[FridgeFreezer]

You can clean them up by removing them and heating the tip with a blowtorch till they glow red, I've "fixed" and tested a few sensors this way before.

As was said above, LR use Titania sensors for various reasons that aren't really important here except for the fact that they cost more, and cheap universal Zirconia ones can't be put in their place

[James NZ]

Hi guys,

Wow what a lot of replies! Thanks very much for the advise, I've decided to leave them alone for now. I should have also mentioned that my disco is a Japanese import, quite common here. To be honest I didn't realise that it would make a difference. At present New Zealand sort of has emission testing, it's not actually measured as such, more of a visual thing like the motor is obviously tired and blowing blue smoke. Ditto for diesels but for rich running (black smoke).

I have duly noted the recommendation for NGK plugs. I fitted the Bosch as I remember them being a good brand and didn't want to remortgage the house to buy NGK's! They are a bl**dy silly price here

I will however get some as today it clocked 120K's so time for a oil/filter change.

I must add that this forum is great. Fixed two problems from searching the forums and everyone seems very friendly so I thought a $$ contribution would be in order.

Cheers, James NZ

[fozsug]

stoichiometric

Great word

[Ally V8]

Hi guys,

Wow what a lot of replies! Thanks very much for the advise, I've decided to leave them alone for now. I should have also mentioned that my disco is a Japanese import, quite common here. To be honest I didn't realise that it would make a difference. At present New Zealand sort of has emission testing, it's not actually measured as such, more of a visual thing like the motor is obviously tired and blowing blue smoke. Ditto for diesels but for rich running (black smoke).

I have duly noted the recommendation for NGK plugs. I fitted the Bosch as I remember them being a good brand and didn't want to remortgage the house to buy NGK's! They are a bl**dy silly price here

I will however get some as today it clocked 120K's so time for a oil/filter change.

I must add that this forum is great. Fixed two problems from searching the forums and everyone seems very friendly so I thought a $$ contribution would be in order.

Cheers, James NZ

Glad its helped - are they still looking after all those lovely oak trees there in Christchurch ?

[mayur]

the 1 wire have volts 0-5 normaly quite low when checking on idle the only diffence between 1 and 3 wires is the two extra wires are for the lambda heater (making more accurate reading faster and less wear)

the 4 wire sensors has 2 wires for the lambda heater (as the 3wire) but uses one wire as a 12v input (and refence voltage) giving a range of 0-12v more accurate and the reason for calling them wideband sensors

theres are 6 wire lambda possibly might find these on the new discos (i know you find them on VWs) where it also give the EGT

[Bowie69]

Sorry Mayur, it's not often I do this, but please re-learn your oxygen sensor stuff from somewhere, because you are spreading a LOT of misleading information.

Firstly there are two basic materials used in oxygen sensors, Zirconia, by far and away most common, and Titania, as used on some Range Rover/Discos (and some others, but this is keeping it relevant to us.), therse are pretty rare

So now we have the materials, we need to talk about the number of wires....

Firstly Narrowband Zirconia sensors:

1 wire, 0-1v, the most basic version.

2 wire, 0-1v, one wire is signal, one is ground

3 wire, 0-1v, one wire (black) signal, one is supplied 12v for the heater, and a shared ground

4 wire, 0-1v, one wire (black) signal, one signal ground (grey), two white wires, one ground and one 12V for the heater.

The output signal is rapid switching between 0 and 1v.

Now, Narrowband Titania sensors:

These give an output of 0-5v, switching from 1000 Ohms to 20,000 Ohms quickly. I'm unsure of the number of wires as they are relatively rare, and of no use to me. But I suspect they are heated and require 4 wires, connected the same way as the 4-Zirconia senssors.

Wideband sensors:

This is a whole different kettle of fish. They no longer switch between 0-1v or 0-5v but deliver a linear voltage between two set limits (0 and 5v or 0 and 12v for example) giving much greater precision for tuning purposes. Wideband sensors generally use zirconia as the sensing element, however there is a lot more to it than just the element in this case.

These have 6 wires:

2 for heater

1 resistor

1 ground

1 pump

1 sensor

I hope this clarifies things a little for you and others, if not, have a read here:

http://en.wikipedia.org/wiki/Oxygen_sensor

and

http://www.picoauto.com/applications/lambda-sensor.html

and if you want more, Google will reveal all.

[Ally V8]

Even the info on the Pico site is incomplete.For instance the type of Titania sensor in a Hotwire injected car gives a 0-0.8v or 1v output where the high end of the voltage range is a rich signal.however on Gems equipped RR's,(And NAS spec Disco 1',Defender D90's) the ecu uses 5 - 0v volt Titanias where the 5v is lean and the 0v is rich.

So you really cannot generalize with them.

None of those earlier types can meassure far either side of 14.7/1 air to fuel so should not really be called wideband.That has changed with the later so called UEGO's,(Universal exhaust gas oxygen sensors)but even these have differences,they usually have 5 or six wires,but I recently had a Disco 3 in with a recurring check engine lamp problem.Its the 4.4 Jaguar v8 and has twin cats and upstream and downstream UEGO's and these are 4 wire ones.This only came to light when I tried to scope them,which I soon realised what they are when I looked at the readings from them.They do not give a varying voltage output,they vary their currnet draw from a fixed voltage to maintain Stoich inside the Zirconia chamber.I've had to buy a Chauvin Arnoux low amp inductive clamp to monitor whats going on.trouble is none of my trade contacts seem to know what I should see so its a bit of a learning curve.

[James NZ]

Glad its helped - are they still looking after all those lovely oak trees there in Christchurch ?

Hi Ally

Yer the oak trees are fine, although its some of the old buildings that are a concern at the moment following our earthquake in September. Have you visited Christchurch?

Cheers, James NZ

[Ally V8]

Yes,we wnet there in 1998 on our honeymoon - had a great time on the south island,one massive playground ! First thing we noticed was the large rows of mature oak trees around town,they must have planted them as soon as they got there.

Hope to get out there again one day,a pommy friend has settled somewhere at the top of the south island and I know a bloke who has a farm down near Ashburton...

I think I'd wear all me bikes out down there if I lived there,the roads are great and the oppertunity for trials bikes must be endless - Heaven !

[James NZ]

Hiya Ally

Well if you do make it down under again you are more than welcome to stay here. We'll show you the best bits of Christchurch and some good 4wd trips into the country. By bikes I guess you do mean the motorised versions. I use to ride Honda's when I was younger, and falling off wasn't so painful. The waimak river was a great place to play.

Cheers, James NZ

[Ally V8]

Yep,thats right - twinshock and Pre65 trials.Thats a kind offer,we will come back to NZ one day,fantastic place.Not sure when it will be though,our time abroad seems to alternate between thew South of France and Western Australia.....