Why the STI is different
A saddle tank straddles the driveshaft tunnel, so it's really two pockets joined at the top. The 2004-2007 STI and the 2008-on cars both use this layout, with a separate level sender in each side. As fuel is used and moved between the halves, one side can read full while the other reads low. Reading only one sender gives you a gauge that jumps around and lies about what's left.
What you want is the combined signal from both senders. That combined curve is what Haltech's calibration data is built around, and it's the one to use if you want an OEM-style fuel level in your Haltech ECU or dash.
Two model-year groups
- 2004-2007 STI: uses its own set of sender data.
- 2008 and later: uses a different set.
Make sure you use the data for your car's year range. The two aren't interchangeable.
The pull-up changes the numbers
A fuel sender is a variable resistor. The ECU turns that resistance into a voltage using a pull-up resistor, and the voltage you'll see at a given fuel level depends entirely on which pull-up is in the circuit. Haltech inputs offer different pull-up options, so the calibration comes in versions for:
| Setup | Use this data |
|---|---|
| Input with a 120 ohm pull-up | The 120 ohm values |
| Input with a 240 ohm pull-up | The 240 ohm values |
| Input with a 1k pull-up | The 1k values |
| Fuel Level Sender Signal Conditioner (HT-038002) | The conditioner values |
The most common mistake we see is entering data for one pull-up while the input is set to another. The gauge moves, but it's wrong everywhere. Decide on your pull-up first, then enter the matching column.
Checking your calibration
- Watch the raw voltage and the calculated level live as you add a known amount of fuel.
- Check at low fuel as well as full; that's where a wrong curve bites you.
- Remember the reading will move under hard cornering and braking, which is normal for any sender.
For the general process, see fuel level sensor calibration and fuel level sensor.
Need the STI sender data tables? Ask us and we'll send them over with advice for your build.
