What the sensor does for your tune
Air gets denser as it cools. A cylinder full of cold air holds more oxygen than the same cylinder full of hot air, so it needs more fuel to hit the same air-fuel ratio. The Haltech reads the air temperature sensor and applies that correction for you, once the air temperature correction map is set up and enabled in the software. It matters most on turbo and supercharged engines, where charge temperature can swing widely between a cruise and a long pull.
If the sensor is reading the wrong air, the correction is wrong too. That's why placement is the part worth getting right.
Where to mount it
You want the temperature of the air that's actually about to enter the cylinders:
- After the compressor and intercooler on a boosted engine. A sensor before the turbo reads ambient air, not what the engine gets.
- As close to the cylinder head as practical, so it reflects the final charge temperature.
- In moving air. The sensor has to sit in the airflow to respond quickly. In a dead pocket it reacts slowly and soaks up heat from the metal around it.
The intake manifold itself can be a poor home, especially toward the rear of the plenum, where airflow is slow and engine heat builds up. A sensor there can read high after a hot idle and throw your fueling off. On many builds, the intercooler outlet pipe just before the throttle body is a better spot.
Installing it
- Choose the location and check there's room for the connector and a gentle bend in the wire.
- Take the pipe or manifold off the engine before drilling. Metal chips that fall into the intake will be sucked straight into the cylinders.
- Drill and tap for the sensor's thread, or weld in a bung such as the M14 x 1.5 aluminum weld fitting on thin-walled piping.
- Wash out every chip, then refit and seal the sensor.
Haltech sensors come in several threads, including the small M14 x 1.5 thread and the large 3/8 NPT thread. Pick the one that suits your pipe or bung.
The 248°F (120°C) ceiling
A Haltech air temperature sensor reads up to 120°C (248°F). Anything hotter is treated as a sensor fault. On some turbo and supercharged engines without an intercooler, or with a very small one, charge air can go past that. If you see it, the real fix is an intercooler, or a bigger one. Cooler charge air is denser, makes more power and keeps the sensor in range.
Once it's in, wire it like the other temperature sensors. Our coolant temperature sensor and internal MAP sensor articles cover the neighboring inputs.
