Member Since: 28 May 2014
Location: Belfast
Posts: 496
4.4 V8 owners fit new O2 sensors
Bit of a long winded tale, but my account of finding and solving a protracted problem of high mpg and O2 sensor readings.
For many years my 4.4 v8 has returned, at most, 11.9 mpg and recently that has been getting worse as bad as 8.6mpg. I always envied anyone reporting better millage. So after reading up on causes of poor fuel consumption I realised my O2 sensors were likely the originals with 120+K on them and should be replaced.
On the 1st of August, having bought new sensors, I set about fitting them. Unfortunately it is not possible to do this without dropping the exhaust system and thus a long process began. It's a relatively easy job, but it has its challenges, especially when doing it on the drive.
The hardest part, aside from being on your back under 3+T of car supported on axel stands, was removing the gearbox support cross member. The 2 bolts on the nearside came off with ease but I had to resort to the grinder to get the nearside 2 off. (and before anyone asks, no I did not drop the fuel tank support as it is possible to work around it) The gear box needs to be supported once the cross member is off and even jacked up to allow the front pipes to drop down past it.
Eventually everything was on the floor (I should mention that I had to use my Draper floor gearbox jack to take the weight of the system below the resonance box) and I was able to manoeuvre it out to the side enough to access the sensors.
I could not pull the system out fully as the rear end was too low to let the rear piped and resonator past.
The two rear sensors came out with ease but the two front ones damaged their threads and I had to chase them out with an O2 thread chaser. New sensors in and the next difficult part began, getting all back together, and after a further 1 - 2 hours it was up and running ready for our 800mile trip to Tipperary, Limerick, Galway and back home to Belfast.
For the first 4 days all was great, never has the 'in cab' mpg meter read as high, 23mpg, but on the day we were to return home, PROBLEMS. Tried to accelerate on the start of the first dual carriageway,............. nothing, just would not speed up and went into a sort of safe mode. Pulled over when I could safely and restarted and all was sort of ok but it was running rough especially when idling. Didn't give it too much thought as it was possible just adjusting to the new data, but over the next week thing didn't improve and there were many fault code for the mixture. The check engine light even flashed up for a short while. Something was very wrong.
A week ago it happened again (safe mode rough running no acceleration) and when I got home I read the fault codes the most telling of which were all those relating to lean and rich mix detected by the REAR (it is very significant that it was just the rear sensors) O2 sensors on both banks with codes P2270 & P2271. When I looked them up I realised I would have to go through the whole process of taking off the exhaust system again to do a smoke test to find leak/s between the front and rear sensors. (Some of you will ask why I didn't just disconnect the front pipes and the answer is, I didn't dare disturb the centre joints as the flange joint was so rusted)
I used a DJ's fog/mist generator (with a hose attached to run the smoke into the pipes), sealed all the opening in the system and inserted the tube. But as misfortune would have it the smoke didn't show the leak. But I noticed moisture leaking out from around the threaded boss of one of the sensors. The smoke generator uses a water based fluid that had condensed around the boss and passed through the problem crack. The weld holding the boss in place had parted company with the stainless steel down pipe for about a 1/3 of its circumference.
I'd found my leak and set about doing a stainless steel weld repair. ( also used a very light smear of exhaust paste around the manifold flange joints on refitting.)
So after working from 10:30 until 4:30 yesterday everything was together again and ready for a test drive after first clearing fault codes. Rechecked fault code on return and all clear, but that was a short run not enough for a good test.
Just went out to top up my LPG and on the way home the 'in car' mpg meter (during the 6mile run) was reading 26.7mpg and still going up. I know these meters are not accurate, but my car has never shown better than 16 on a run while I've had it. Based on this new high mpg reading I would recommend that anyone with an older car, or with greater than 80,000 miles on the clock, has the O2 sensor replaced.
I'm not sure why the leak didn't show up on any previous reading of faults, or maybe it did but was lost among the many other faults present.
21st Aug 2017 3:20 pm
plocker
Member Since: 14 Mar 2016
Location: Preston
Posts: 828
I would be interested to know how many miles you are getting from a tank rather than the dash figure.
If this has increased by 80 miles or so I would be more than interested in changing my sensors.05 V8 HSE Bonatti Grey
23rd Aug 2017 3:26 pm
Alphamale
Member Since: 28 May 2014
Location: Belfast
Posts: 496
Yea, I know the dash indication is well known for it's optimistic readings and so I will be interested in the results at the next fill up myself.
As most of my driving is in town that will be in about 120 miles, not because that's when I expect the tank to be empty, but rather because that's when I'm used to topping up on the old fuel usage rates. LPG gauges are not very accurate and so over time you get to know how yours performs and if there is a good improvement I'll have to relearn when I need to top up.
23rd Aug 2017 7:52 pm
Mogwyth
Member Since: 03 Oct 2014
Location: Pwllheli
Posts: 3976
You should have done a decat while they were off
Mine does around 250 to a tank on LPG, which at 75l gives an average mpg of 14.58, dash shows around 17.3. Dont use petrol much so cant say what it does, just that its a bit more.==================================
05 D3 HSE V8 4.4
04 MG TF 135
03 MG TF 115 Cool Blue Edition
02 MG TF 160
00 Hymer B564 Lionheart
1971 Series III 109
23rd Aug 2017 9:03 pm
Discoveringcomfort
Member Since: 16 Sep 2015
Location: Berkshire
Posts: 637
Mines the same as this if it is used on the motorway! But only 180 if local or spirited driving.Series 1 V8
Series 2 Hibrid V8
Discovery 3 HSE V8
23rd Aug 2017 9:40 pm
Mogwyth
Member Since: 03 Oct 2014
Location: Pwllheli
Posts: 3976
That should have been 240 And is a mix of rural (loud pedal used when possible ) and town, motorway goes up to about 260.==================================
05 D3 HSE V8 4.4
04 MG TF 135
03 MG TF 115 Cool Blue Edition
02 MG TF 160
00 Hymer B564 Lionheart
1971 Series III 109
23rd Aug 2017 10:11 pm
Dr Jones
Member Since: 20 Feb 2012
Location: Pretoria
Posts: 55
Replaced mine early last year but unfortunately it did not make a difference to consumption in my case.
BTW it is possible to replace them without dropping the whole exhaust. The Right Top one can be accessed via the wheel arch if you remove the heat shields partially.
24th Aug 2017 11:35 am
Ruper
Member Since: 28 Jun 2019
Location: Virginia
Posts: 318
Removing front sensors
I am going thru cleaning mine, as I do not have the funds cleared for a set of new ones. I got to the rears fine, with a little skin removed I tried to get at the fronts (Upstream). The truck is on ramps right now so not sure I can go thru the wheel arch unless I reset everything. I am removing to clean and check them only right now, so I gave up on the upstream ones for now.
You say you got at the right front via the wheel arch, how about the left front?
Is there a write up? I checked youtube and Birt Atl. had one, but they pulled it for reasons unknown.
Could someone do a quick hit on removing the front upstream sensors? Is it just jack the front and remove some wheel arch covers and heat shield from there both sides? Really am not going to drop the exhaust for a half @$$ cleaning. Repcing the rear downstream this AM. WIth liberal amounts of anti-seize used.2005 Land Rover D3, 4.4L V8, Maya Gold Metallic
1966 Scout 800, 196 cu.in.
1975 Scout II, 392 cu.in.
12th Aug 2019 2:59 pm
MintyHit
Member Since: 25 Jul 2017
Location: Bradford on Avon
Posts: 227
Mogwyth wrote:
You should have done a decat while they were off
Mine does around 250 to a tank on LPG, which at 75l gives an average mpg of 14.58, dash shows around 17.3. Dont use petrol much so cant say what it does, just that its a bit more.
Pretty much identical figures to mine... 80l of LPG is the most I've ever managed to fill it and 250miles is the most I've had before switch-over back to petrol.
Does this sound about right or two I need to spend 3 days taking my exhaust system apart?
12th Aug 2019 3:09 pm
Mogwyth
Member Since: 03 Oct 2014
Location: Pwllheli
Posts: 3976
Seems ok to me 30,000odd miles in since getting mine and mpg only alters if I try hard.==================================
05 D3 HSE V8 4.4
04 MG TF 135
03 MG TF 115 Cool Blue Edition
02 MG TF 160
00 Hymer B564 Lionheart
1971 Series III 109
12th Aug 2019 4:16 pm
Alphamale
Member Since: 28 May 2014
Location: Belfast
Posts: 496
Ruper,
My advice would be to leave-well-alone. If you're not getting any problems they're probably OK. You're only looking trouble by trying to get them out as they have a tendency to be so seized that you wreck the threads and may need to have a new mounting flange welded in.
I just got away with it, the treads were damaged but serviceable and the only reason I dropped the front pipes was because of an air leak around the base of the O2 mounting flange that I had to weld up.
If you must take them out you can either go in through the wheel arches, after removing all the heat shields (you need to do that anyway to free the multi plug), or reaching up from underneath. Either way it's difficult, but wheel arch is easiest. I went in that way and used O2 sensor wrenches like (but not particularly) these ones https://www.amazon.co.uk/FreeTec-8-Inch-Of...&psc=1
I also recommend that if you decide to change any and fit new ones, ONLY FIT GENUINE LR ONES. I went through 4 sets of sensors in 6 months from Denso and Britpart and they all failed. Only the LR supplied ones have worked and they're by Denso?? doesn't make sense but ones direct from Denso failed.
12th Aug 2019 5:10 pm
MintyHit
Member Since: 25 Jul 2017
Location: Bradford on Avon
Posts: 227
Alphamale : How's the increased MPG worked out long term out of interest?
Are you getting significant gains now after changing your o2 sensors?
14th Oct 2019 10:36 am
Alphamale
Member Since: 28 May 2014
Location: Belfast
Posts: 496
Not really, while I can manage between 18 and 20mpg on a tank of gas(LPG), when on a long run. I'm only getting 11mpg normally, but that's because I mostly drive around town, doing short stop start journeys.
Thankfully I run on LPG as it takes the sting out of the running costs. though it has its drawback too, particularly the 10% or so, less milage than petrol.
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And is a mix of rural (loud pedal used when possible 
) and town, motorway goes up to about 260.
