Rover 820 Mpi Lucas Hotwire Efi: Fuel Temperature Sensor
If removing this component allow the fuel rail time to depressurise and the engine time to cool to reduce the danger of a serious fire before slackening even then cover the union with a cloth as you slacken the fitting.
Location: In centre of fuel injector supply rail, at the rear of the engine above inlet manifold.
Function: To supply information to fuel ECU on fuel temperature, to prevent vapour locking of the fuel injector system.
Operation: If temperature exceeds a pre-set high limit the fuel ECU leans the mixture by reducing the injector pulse width and increases the idle speed by operating the idle control stepper motor, this action should only normally be triggered in combination of extreme summer heat and heavy traffic.
Sensor Type: Standard NTC Thermistor -- resistance reduces with temperature. Electrical characteristics appear very similar to CTS (coolant temperature sensor). Note some earlier version of the Lucas injection system fitted to the Montego Efi and early 216 Efi used a normally off switch instead of thermistor.
Connections: Two wire.
Likely Failure Mode: May trigger the Fuel ECU to early causing rich mixture and fast idling.
Testing: With engine fully warm and idling disconnect sensor -- engine note should not change.
Then with sensor disconnected place a 100 ohm resistor across the terminals of the plug, if fuel ECU and idle stepper motor are operating correctly idle speed should increase by 50 RPM and mixture should become richer.