The water temperature sensor is used mainly for cold start compensation with fuel and spark timing graphs. There is however a couple of functions that requires compensation with temperature like idle control, accelerator pump, prime pulse etc. Neglecting to wire the sensor in may result in the engine not being drivable when it is cold. All fuel injected engines have water temperature sensors mounted in the thermostat housing area. Not all are compatible with the Spitronics ECU but there are aftermarket sensors that can be fitted. Spitronics ECU’s use a 2K NTC (Negative Temperature Co efficient) resistor. It is the standard under water sensors for most engine manufacturers. It has a fixed calibration curve which is programmed in the firmware and it cannot be altered. It can however be slightly calibrated by giving it an offset percentage. The normal setting is 100%. Click on the calibrate button left of the Water sensor check box.

Reduce or increase the value to slightly shift the reading value. Do this at the critical temperature for instance where the fan must come on or off. If the error is too large you may need to replace it or get the correct sensor. These sensors are measured at 25°C with an ohm meter to see which type it is. If you have the wrong type you may need to change the sensor to a 2K sensor. Save to ECU button will make the changes permanent.

You may be required to do adjustment tuning in the winter and then in the summer. Remember to enable it on the active sensors page. When the engine is used in the winter, you may advance the timing slightly as the fuel burns at a slower rate. The fuel must be increased till the engine runs properly. Especially for racing fuel It may even require a richer mixture for these conditions. In the hot engine condition, you may retard the timing and increase the fuel. A richer mixture helps to cool the engine down. The thermostat controls maximum temperature so it may be difficult to tune. Nevertheless, put some extra fuel and less timing in the graph.

Water temperature correction can only be done in the morning when the engine is at its coldest. To set this graph, start with the example below. Now start the engine and let it idle. Adjust the AFR to be on the rich side. You may later have to tweak prime pulse, start enrichment and accelerator pumps to get a smooth pull off and start when cold.

Water Temperature Graph