O2 sensors

Mogwyth · Post by **Mogwyth** » Sun Apr 24, 2011 12:28 pm

So the ECU was not at fault so back to square 1.

The motor won't go closed loop and the O2 sensors were almost constantly sending a lean signal back to the ECU.

I found a molten but not blown fuse that covers the feed to the heater circuit on the sensors, but as yet found no cause, after replacing this the voltage reading on the feed to the sensor reads a steady 12.3volts at the sensor socket.

Now the 02 sensors sort of work but not consistently:
Sensor Readings

As you can see the default value seems to be lean, I thought open loop would be in the middle, but could this be a symptom of O2 heaters not working properly noting that when you raise the revs (and consequentiality the exhaust temperature) they seem to start working.

Any thoughts?

Cheers

Bill

Discovery II 4.6 V8 Auto.

DEVONMAN · Post by **DEVONMAN** » Sun Apr 24, 2011 2:12 pm

Bill.
If they are 3 or 4 wire type sensors, check the earth to the heater circuit.

Regards Denis

Mogwyth · Post by **Mogwyth** » Mon Apr 25, 2011 8:04 am

They are 4 wire, the wiring diagrams are a bit unclear as to how they are earthed.

Cheers

Bill

DEVONMAN · Post by **DEVONMAN** » Mon Apr 25, 2011 9:38 am

Mogwyth wrote:They are 4 wire, the wiring diagrams are a bit unclear as to how they are earthed.

Cheers

Bill

One of the wires should be black. This wire is connected to earth/chassis.
With both the connectors disconnected, check with a meter that the black wire on each connector (Loom side not sensor side) is earthed.
You have already said that you have a 12 volts supply to the sensor.
Do not do any tests on the white sensor wire unless you have a digital voltmeter or you may damage the sensors.
Regards Denis

Mogwyth · Post by **Mogwyth** » Mon Apr 25, 2011 10:36 am

Therein lies the problem, no black wires:

DEVONMAN · Post by **DEVONMAN** » Mon Apr 25, 2011 11:48 am

All the four browns should have a good earth.
regards Denis

Mogwyth · Post by **Mogwyth** » Mon Apr 25, 2011 12:19 pm

The four brown wires are the live feeds from fuse 2 for the heaters

DEVONMAN · Post by **DEVONMAN** » Mon Apr 25, 2011 12:26 pm

Mogwyth wrote:The four brown wires are the live feeds from fuse 2 for the heaters

Ok, then all I can suggest to check if the heaters are connected is to remove the fuse and check the amps flowing across the fuse holder.
No flow will mean the heaters are not working.

Regards Denis

Mogwyth · Post by **Mogwyth** » Tue Apr 26, 2011 2:56 pm

OK, now I am very confused the diagnostics done on Saturday revealed a consistent lean reading from the sensors which went rich if I restricted the air flow and flipped a bit after raising the revs. Now it's showing constantly rich, and will only go lean if you increase the air flow (removed the oil filler cap) and again will flip if the revs are increased!

Bill

DEVONMAN · Post by **DEVONMAN** » Tue Apr 26, 2011 7:48 pm

Mogwyth wrote:OK, now I am very confused the diagnostics done on Saturday revealed a consistent lean reading from the sensors which went rich if I restricted the air flow and flipped a bit after raising the revs. Now it's showing constantly rich, and will only go lean if you increase the air flow (removed the oil filler cap) and again will flip if the revs are increased!

Bill

Are you waiting for it to warm up fully before tests?
Regards
Denis

Mogwyth · Post by **Mogwyth** » Tue Apr 26, 2011 8:33 pm

Yep.

Start up went to 1248rpm. Pre-cat sensors climbed quickly to 0.900vs and held around that. The engine temp reached 76 degrees after 5 minutes then the post-cat sensors went from 0.454 to around 0.900. As before (when it was reading lean) revving the engine induced short periods of switching, engine temp was by now in the mid nineties. This was when I did the oil cap test and all sensors then read very lean but no obvious attempt by the ECU to compensate and sensors only returned to rich when the cap was replaced.

Could this be Throttle Position Sensor issue?

Mogwyth · Post by **Mogwyth** » Thu May 12, 2011 10:16 pm

Getting to serious despair time, just can't find what's wrong with this setup.

We have replaced all four 02 sensors, throttle position sensor, Engine Coolant Sensor, MAF and the ECU, checked for air leaks etc to no avail.

I don't know if this says anything to anyone:

Anyone know of a Land Rover V8 expert in North Wales, further West the better.

Cheers

Bill

Mogwyth · Post by **Mogwyth** » Sat May 14, 2011 11:55 am

Just had the MOT done passed no problem. Tested on LPG CO2 0.047% and HC 62ppm.