Why measure fuel temperature?
A return-style fuel system constantly sends fuel past a hot engine and back to the tank, so fuel temperature climbs through a session. On a long track day or a hot street drive that can mean less dense fuel, a leaner mixture and, in bad cases, vapor in the lines. With a sensor on your Elite you can:
- Log it, so you can see whether a lean trend lines up with rising fuel temperature.
- Warn on it, with the gauge flashing in ESP when it moves outside the range you set.
- Protect the engine, by tying a sensor fault into engine protection.
Most fuel temperature sensors are two-wire thermistors: one signal wire into an analog voltage input and one signal ground. If you run E85, a flex fuel sensor can also report fuel temperature.
Wiring tab
Choose the input type
| Input Type | Pick it when | Needs |
|---|---|---|
| Analogue Voltage | The sensor maker gives calibration data as voltage vs temperature | An AVI |
| Analogue Resistance | The sensor data sheet lists resistance vs temperature (common for thermistors) | An AVI |
| Thermocouple Type K | You're using a K-type thermocouple | A thermocouple amplifier such as the TCA2 or TCA4 |
Pick the input and set the pullup
Assign the sensor to an AVI whenever you have one free. An SPI can stand in when you've run out of AVIs, but there are differences:
| AVI (preferred) | SPI (fallback) | |
|---|---|---|
| Pullup | 1k to 5 V | Weak 10k to 5 V |
| Sensor Type | n/a | Hall Effect |
| Calibrations | Stock ESP calibrations work as-is | Pre-installed temp calibrations need adjusting, because the pullup value is different |
Pullup rule of thumb: enable it for a plain two-wire sensor, disable it for a sensor with its own power supply. If the sensor is also wired to a factory ECU, as in a piggyback install, the factory ECU normally already supplies the pullup, so switch the Haltech's off to avoid two pullups skewing the reading.
Calibration tab
ESP comes with a set of temperature calibrations. Load one with the Open icon, or type in a custom curve from the sensor maker's data and save it with the Disk icon so you can reuse it on the next car. If you pick the wrong curve, the sensor will read but the numbers will be wrong, so sanity check it: a cold car that has sat overnight should read close to the air temperature.
Display tab
Warning Minimum and Warning Maximum set when ESP gauges for this channel flash red. We set the upper limit a little below where we've seen the car start to go lean or misbehave, so you get time to back off. The low warning is mainly useful for spotting a sensor that has failed or come unplugged.
Diagnostics tab
These settings help the ECU tell a real reading from a wiring fault. Both default to disabled.
| Setting | Code | Trips when |
|---|---|---|
| Temperature Raw Min | P0182 | Input voltage falls below your limit (typically a short to ground) |
| Temperature Raw Max | P0183 | Input voltage rises above your limit (typically an open circuit or unplugged sensor) |
With engine protection active, you can give each code a DTC severity, so a failed sensor can trigger whatever protection level you've set up. Choose the voltage limits just outside the range the sensor ever reaches in normal use. See the DTC index for other codes.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reads extremely cold at all times | Open circuit or unplugged sensor |
| Reads extremely hot at all times | Signal shorted to ground |
| Reads, but the numbers are off | Wrong calibration, an SPI used with a stock calibration, or two pullups on a shared sensor |
Related sensors: coolant temperature, ambient air temperature and fuel return flow.
