V8 O2 sensors?

I have a 1996 V8 with cats. Recently I have been loosing power, using to much fuel(even by V8 standards) and am stalling all the time.
2 days ago 1 of the down pipes broke in 2, I took it apart and :
The inside of 1 downpipe and the same o2 sensor was black, the other looked as if it had been steam cleaned inside.
Is it possible the black o2 sensor has failed and the ECU is injecting to much fuel into 1 side of the engine?
Robert Taylor

Sounds like the black coloured one is failing to switch down from 5v (lean) which makes the ecu widen the pulse width of the injectors in an attempt to richen the mixture - if the ecu then fails to see a rich signal it will carry on widening the pulse to the limit of its parameters - hence the high fuel consumption,poor power output.
The other sensor,you say it looks steam cleaned - it possibly has been if the engine is using coolant, with split headers the feedback from the oxygen sensors will be seriously flawed.Everything needs to be present and correct to get the sensors switching properly and achieving true closed loop operation.
You really need to get it all back together with no manifold leaks,(inlet or exhaust) and all vacuum /breather hoses sorted before you write off either or both sensors.With the engine at running temp they should be switching from 0-5v and back again in 1 sec and less at a constant engine speed - less as engine speed increases.This can be measured on the black sensor output wire with a decent multimeter - or better still an oscilliscope.Sorry to dribble on but this needs to be happening or your engine will not give good power/mpg or pass an MOT.
Good luck !

Thank you for your e-mail. The down pipes are together again and I can not find any leaks any where, I will test the black wire from the o2 sensor tomorrow. I have not put in any coolant since before last winter, so I know it is not using any water.
Thanks for your help
Robert

Hello Eightinavee
I have tried to test the black wire coming from the o2 sensor but I am not sure if I am doing it right! I disconected the sensor at the connector (why do they make the wire so short) and tested the black wire from the sensor, with the engine running and at full temp. No voltage ? does the o2 sensor create voltage ? should I leave it connectd and test somewhere else ? When I dissconected the sensor there was no change in how the engine ran, is this right?
Need your help
Best Regards
Robert

You need to leave the sensor connected whilst testing - they are heated via an internal element,and would only be hot enough to switch when revving/working hard.Probe the sensor wires with a pin then attach your MM lead to the pin.If the engine was hot when you disconnected the sensors within a few seconds it should start to faff around - esp at idle.
Check the sensors are being heated - 12v should be present at one of the sensor wires whilst it is running - the other remaining wire is the earth.Think red is 12v and white is earth - long time since I did one,but it all should be obvious when you get to it.
Good luck !

Many Thanks
I will try tomorrow, E-mail you soon
Thank you
Robert

Hello Eightinavee
Sorry I took so long to get back to you. Finaly got round to testing the O2 sensors.
With the engine cold I Have 13.8 volts on the red wire, nothing on the other 2.
Problem is with the engine hot and running at 2000RPM I still get the same reading. is this O2 sensor failure on both sides !?
Robert

Could be but did you check they are both earthed ? If they are then the sensors are not switching up to 0.8v (rich).You need then to prove that they are capable of switching,with the engine running clamp off the fuel return pipe for a couple of seconds,if that does not make them switch up to 0.8v,then yes they are shot.
My last job of the day today was a 98my 3.9v8 - with a high Co reading,Mot fail.10mins with the oscilliscope showed that the Lh sensor was dead and the Rh one worked but was lazy.A pair of sensors should make the thing run twice as well and get the emissions right down - whe they are running properly it amazes me how good they can be for what is now a simple out-dated system.

Hello Eightinavee
I ordered 2 new 02 sensors almost a month ago, they have just arrived, problem is they have 4 wires, white, red, black and yellow! Plus a different conector, the sensors look the same.
They are Britpart corresponding to ERR1834, I ordered them by post from the UK because the local Landrover dealer wanted 200 pounds each and John Craddock only wanted 69 pounds each!
Have you come across 4 wire sensors before? any idea's on what I should do?
do they need to go back?!
Thanks again for your help
Robert

You need to send them back,they are for 95-97my 4.0,4.6 v8 Range Rover with Gems injection system.Your car needs ERR6729 sensors for its 14 Cux injection system.They are not interchangeable,you could also order them from an NGK/NTK stockist,part no, OTD3G-3A1. Stock no 0453.
Good Luck !

Hello Eightinavee
Success at last!!!
I sent he sensors back to Craddock but they wanted 100 pounds each for the new ones, so I bought them on line (oxygensensors.com) in the states for 59 pounds each (shorter delivery time) and the car now fly's, also no more stalling, and the engine is so quiet!
Thank you so much for your help.
Vroom, Vroom, Robert58.