strange issue with Defender Td5 temperature gauge

[LarryK]

On my Td5 the temperature gauge never rises very far outside the cold zone but whenever I press the accelerator pedal the needle on the gauge drops into the blue/cold zone immediately, then rises again as soon as I take my foot off the accelerator.  There seems to be a direct link between the accelerator pedal and the position of the temp gauge. Since this problem manifested itself I've flushed the coolant, replaced the thermostat, installed a new coolant temperature sender and refilled and bled the cooling system but the temperature gauge is still affected by the accelerator pedal movement. I've cleaned all the battery and engine earth connections and the contacts at the temperature sender but this hasn't made any difference and the contacts looked OK before cleaning anyway. I'm thinking that there's a short somewhere or possibly an ECU glitch, electrics is not something I'm good with. I did have a small drop of engine oil in the red ECU wiring connector socket so I fitted a new injector harness and I don't think any oil got into the ECU. This temperature gauge (linked to accelerator pedal position) problem has me baffled, any insight into to the possible cause of the issue would be appreciated, it may be a short so if anyone knows if or where the accelerator pedal wiring could make contact with the temperature gauge wiring or any other reason why the temperature gauge would drop instantly on pressing the pedal and rise again as soon as the pedal is released I would be most grateful. Thanks, LarryK

[RedLineMike]

i would suggest running an additional earth wire from the ecu mounting plate to the negative on the battery terminal,

 

[LarryK]

16 hours ago, RedLineMike said:

i would suggest running an additional earth wire from the ecu mounting plate to the negative on the battery terminal,

 

Thanks RedLineMike, This evening the temperature gauge resumed behaving normally. I think that the problem may have had to do with engine oil in the loom but that's only a guess. I had the old injector loom disconnected for a few days while awaiting delivery of a new injector loom and had the red plug disconnected from the ECU at the same time and had been spraying brake cleaner into the engine loom in the hope of clearing the oil. When I installed the new injector loom a few days ago the temp gauge continued to fluctuate but I noticed this evening that it has rectified itself, maybe it took a while for the ECU to learn that a new injector loom or a new coolant temperature sender had been fitted or perhaps the engine oil has now fully worked its way out of the engine wiring loom. I'll keep an occasional check on the loom/ECU connection for further traces of oil. If any further electrical gremlins emerge I'll try your suggestion of running an earth wire from the ECU mounting plate to the battery negative terminal. Thanks for your help.

[LarryK]

On 5/23/2020 at 10:28 AM, RedLineMike said:

i would suggest running an additional earth wire from the ecu mounting plate to the negative on the battery terminal,

 

Yesterday I helped a friend to jump start his car as his battery was discharged after a long lay-up. Soon afterwards I noticed that my temperature gauge needle was behaving erratically again, the needle would fall back to the left every time I pressed the accelerator pedal, I'm guessing that the jump start interfered somehow with my ECU. Today I followed RedLineMike's suggestion and ran an earth wire from one of the ECU mounting screws to the battery negative terminal and the temperature gauge has been acting normally again since this modification. Thanks for the tip RedLineMike, LarryK