The Ecu then sends commands to the fueling and ignition systems according. If the sensor is faulty and thus sends incorrect , or no info to the ecu as above, the fueling etc will be incorrect and thus do as you describe resulting in poor mpg.
If you remember the old auto and manual choke systems.. (on petrol engines - but the principal is the same ) ..it works like that , only electronically.. If and when the choke was in the wrong position for the temp of the engine, the engine performance would suffer and if it were not adjusted right , slightly "On".. then increased Mpg ....- exactly the same.
So, without the aid of plug in diagnostics at the moment and the results thereof - its well worth renewing that sensor. Its usually located on the front right of the engine head - under the plastic cover... I will give you a pic / drawing below which shows its location for you ... identified by a red dot !
Other than the things mentioned above which should all be considered - I would suggest renewal of that sensor and try it from there... IF you were still to have trouble after that , then proper diagnostic tests would need to be done to check the rest of the engine management system through.... but the Ect sensors are a common issue....
Here is the drawing / location for you for the Ect sensor..
Kind Rgds, MIKE
Feedback and any Bonuses are always appreciated too. Thank you.
Thanks for the reply. I had already asked the garage to fit a new thermostat and it seems the ECT sensor is integral with that.
The result has been an increase in the running engine temperature to around 95 Deg C and an improvement in the low speed consumption, say speed not exceeding 50 mph, but the consumption over this speed remains conspicuously high.
I am beginning to believe that the car is incapable of decent mpg and were it not for the fact that I own an older model with virtually the same engine would simply sell.
Do you know what other sensors feed back to the ECU?
Is it possible to have the ECU re-programmed, that is the same program uploaded and re-written?