We all know the only thing an XJR6 cannot pass is a gas station.
However, mine is drinking excessive amounts of fuel. Spark plugs look sooty (NOT due to oil consumption).
Wallet is looking anorexic.

Suggestions on possible causes?

Thanks

 

The engine regulation ( mixture or short term fuel trim ) must go into closed loop by seeing the engine coolant temp reach 165 degrees C abouts

Try changing the very cheap ECT sensor that can be calibrated against a chart on page 78 of the 801s doc

801S TITLE

If you ever change the thermostat , never install the large O - ring even if it comes with one , cracks the casting ears

 

Can you read the LTFT from the OBD2?

It will help diagnose your issue...

When is the last time you changed the oxygen sensors?

 

Bed time in USA but ask questions for morning

Your LTFT and STFT is target 0 % although not perfect




There is 1 fuse controlling the all 4 O2 sensors preheat to read correctly ( sensor physics )


Fuse # 10 , 12 , 14 , or 16 right engine bay fuse box , only 1

Only the rear 2 sensors regulate engine so you have a swapping option although they don't last forever , there are some clean ups of the grounds to improve signal

To read the heater on your hard to get to SC you can read them at the Engine ECU ( red connector ) of approx 600 ohms , and there is the Papa Indy 61 connector position 12 ( White / Green wire ) subject to a TSBs on corrosion , heaters are 1/ 2 the problem and can be easily read through the sensor and then you know

Connector ready Bosch # 13789 as replacement along with a Walker # Y , originals are Densos




There is also the not getting anti - seize on the tip of the sensor besides the cleanliness of the sensor ( carbon buildup which may be cleaned with Seafoam ( ? ) ), so you have a cart before the horse , clean sensors first or fix engine regulation to not be rich , antifreeze head gasket leaking into exhaust will also harm sensors as a white ( ? ) color change on the tip

Do not twist O2 sensor wires as galvanized and brittle , I had broken wire strands sticking out of insulation from previous owner , the crush washer seems to have an effect from a X300 example in Boston somehow , 12 mm different than the spark plugs 14 mm

 

There is also the crossing of the O2 sensor connectors as they are physically the same , many have done and there where correction results

On the above O2 sensor wiring guide the 4th wire color is different on the car side , so you are looking at the U , R , G , N sensor itself return wire

You would have to use this pic to be physically following the pipes

 

Crossing sensors would give a rough ride.

OBD2 readings would also confirm whether car is getting to closed loop. There could be something off, like a failed coolant temp sensor that would cause the car to stay in open loop....overfueling the car while giving you a normal ride.

 

The $ 25 ECT sensor would be easiest !st try without a ECT reading and cleaning up the O2 sensor circuit would not hurt in general housekeeping of that system

The grounds to clean are the small ground post on the rear engine firewall , the external ground strap on the ECU case , and maybe the large ground strap between the starter and car frame

I had green in the O2 sensors connectors

Maybe an ECU connectors check , look for on each socket 2 pinching tabs as a lot of mine only had 1 , the heaters pins are X and Y