Why measure fuel temperature?
Fuel heats up as it circulates past a hot engine and back to the tank, especially with a return-style system on a car that's been idling or running laps. Warmer fuel carries a little less energy per unit volume, and very hot fuel can start to vapor lock. Logging fuel temperature helps you connect odd behavior with heat soak, spot a fuel system that's getting too hot, and, through engine protection, react if it ever gets dangerous.
Most fuel temperature sensors are two-wire thermistors: one wire carries the signal to an analog input and the other goes to signal ground. If you're running E85, a flex fuel sensor can also report fuel temperature.
Setting it up in NSP
The Fuel Temperature function has four nodes. We'd work through them in this order:
1. Wiring
Assign the sensor to any free AVI. Enable the Pull Up, which switches in an internal 1 kOhm resistor from the signal input to 5V. A two-wire thermistor needs that reference to produce a readable voltage.
2. Calibration
Load the calibration for your sensor. If it's a Haltech sensor, use Load from File to drop the correct data straight into the table. For anything else, enter the manufacturer's resistance or voltage versus temperature data by hand. Use Save to File to keep a copy for future builds. Once it's loaded, check the reading on a cold engine: fuel temperature should sit close to ambient air temperature.
3. Display
Set Warning Minimum and Warning Maximum. When fuel temperature goes outside that window, any number display, gauge or bar showing the channel switches to its warning state. The high limit is the one that matters; set it where you'd want to know the fuel is getting hotter than normal for your system.
4. Diagnostics
Enable the high and low voltage DTCs to catch wiring faults like an open circuit or a short. You can give each one a DTC severity, and that severity decides which engine protection level it triggers. For a wiring fault on a monitoring sensor, a low severity that just logs the problem is usually enough.
Quick troubleshooting
- Reads extremely cold: often an open circuit or unplugged sensor.
- Reads extremely hot: often the signal shorted to ground.
- Reads wrong but steady: pull-up disabled or the wrong calibration loaded.
Other sensors set up the same way include fuel pressure and ambient air temperature. On an Elite ECU, see the ESP fuel temperature sensor page instead.
