Oxygen Sensor Problem

Hello
I have a 2002 Discovery V8 with LPG purchased a few months ago with no useful history so still sorting it out.
Current problem (thank you Hawkey Diagnostics gadget) is "P0150 O2 probe pre-cat bank 2".
This sensor was just last week replaced by my local Indie (it was towed in by RAC with crankshaft sensor failure) and he noticed the failed O2 sensor causing rough running - at the same time I had him fit new Magnacor leads (small hand req'd).
All ok at first, much smoother, but now that new O2 sensor has failed in the same way.
Looking at live data it starts at about 0.4v and fluctuates very slightly and as it warms up over a couple of minutes or so drops to 0.0v and stays there.
Consequently very rough engine running very rich.
Am I unlucky and have a duff replacement O2 sensor or is there something else I should look at. Presumably he fitted the correct part in the correct way.
I am tempted to buy another new one and fit it myself as it does not look too hard to get at and having been done once will be loose.
Where does the cable run? It seems to go up the back of the engine but I could not see.
All advice gratefully received....
Les

Hi Les, Out of all the replacement O2 sensors i have replaced and thats a few( used to own a garage), I have only ever had 1 faulty 1 and that was my fault,the wiring rubbed against the body and chaffed through.

Has the mechanic cleared the fault code?

If he has, try swapping the O2 sensor from the other bank and putting the sensor you think is faulty in there.Run the car and if the engine management light comes back on get him to check it again. Fault should now be on Bank 1 ,not Bank 2.

If fault is still on Bank 2, Its not the sensor....Check wiring

Thanks, that is logical (swap sensors to see if fault moves with sensor).
I cleared the fault codes myself but they came straight back.
Will have a look to see how easy the bits are to get at as swapping around could be a pain.
I have read suggestions that both sensors should be replaced as a pair but that does seem excessive.
Les

Give m2e 2 minutes and i will tell ya how easy they are to swap ...i got a 2002 v8.

Just had a look at mine.....They are a doddle to swap over.

Thanks Wolfy Dave.... "a doddle to swap over".... I don't think so!

Getting at the drivers side sensor is not easy but with some effort can be got at ok.

But getting at the connector block that the lead plugs into was nigh on impossible even for my double jointed son who has smaller hands than my big ones. The multi-plug connector is held onto the back of the engine against the bulkhead and a pig to get at. It would have been so easy for the engine designers to lengthen the cable by a few inches and put it in a much better place (Coil pack is another example!). What made it particularly hard in my case is the LPG installation with its extra pipes and vapouriser which fill what little space was there originally.

Finally got the connector off its clip and pulled the two plugs apart and have decided to re-site the cable run to make it get attable in the future, no way am I going to put it back on its original clip.

The multiway plug was full of oil - very full - there is a leak at the back of the engine somewhere and it has run down the wire straight into the plug. I hoped a good clean out would fix the problem assuming that the oil was causing a short but the sensor still malfunctioned.

Next was to remove the sensor from the exhaust and not surprisingly it was heavily sooted from that bank running so rich. I tried cleaning it but it did not make any difference.

By now pretty knackered so decided not to swap with the working sensor from the other bank as originally planned but just buy a new one. I don't want to risk upsetting the "good" sensor for the sake of saving a few bob.

My assumption is that the oil leak into the cable connector messed up the signal voltage causing the engine to run rough and extremely rich on that side sooting up the sensor.

A new sensor should be with me on Tuesday - fingers crossed that sorts it. I will let you know.

Les

Hi Les, I have just got back in the house,been and swapped both front O2 sensors to see how long it took. It has taken me 40 minutes...The connectors blocks are a little difficult but i managed ok....I had no problems with the drivers side 1 like you have had.My LPG system still gives me the space to get my hand and arm in maybe you had problems because of the position on your LPG..

I think you are doing the best thing by replacing the sooted up sensor.An idea,if you can get your hands in of course would be to clean out the sensor connector with something like brake cleaner to get rid of the oil in the terminals.

Dave

Wolfy Dave will forever now be known as "man with long arms and small hands" (smile). My LPG installation really did get in the way.
Replacing the O2 sensor has solved the "way too rich" problem and rough running. The lead on the new sensor (proper landrover part - MHK100920) is about an inch and a half shorter than the old one. I have not extended the leads to make access easier, just left it dangling, will tie it back to keep it away from the manifold and melting.
So I reckon it was oil contamination in the multiplug which killed the signal and then sooting up that killed the sensor. Lets hope this one lasts.
Incidentally... I bought the new part from Marshall Land Rover (parts dept obviously) in Cambridge who got it in for me from another branch same day and the price was £58 + vat which I thought was pretty good and not the robbery I was expecting from a main dealer. Same price as Rimmer Bros but without the delivery charge.
Very happy with "Hawkeye" diagnostic kit.
Thanks for the hand holding Wolfy..
Les

Hi Les, Glad to hear that you have got it sorted and that price from the dealer was very reasonable indeed. Im off on holiday tomorrow for 2 weeks but when i get back i will make up a couple of plugged extension harnesses for you so that you have a little bit more room on the cables for next time

Dave

I had a problem with running on LPG, missfiring and back firing after over run.

No problem when first starting but when warm ie when the car switched to closed loop it was a beast.

LPG could not be adjusted to compensate so changed both o2 sensors but still a problem. I desperation and from advice from a LR techi I ran it with both o2 sensors disconnected and it's been fine ever since. NO noticable change in MPG or power.