ECU ground connection

Hi, I have a question. According to the grounding instructions for the star point, the ECU ground pins should not be connected directly to the battery. However, in the FT450 manual, it says that pin 12 of the ECU must be connected directly to the battery and should not be connected to the chassis or the engine, and the same applies to the power ground on pin 7. What should I do?

Connect it directly to the battery.

I do this with most ECUs, as it's the best grounding point to avoid noise.

With most ECUs—especially at the higher end—this isn’t an issue, and the manual will typically only mention the need for a good ground, rather than stressing the importance of grounding directly to the battery. You’ll find that most harnesses are built with best practices in mind, such as star-point earthing, in these cases.

Unfortunately, I can confirm that for ECU brands that emphasize wiring directly to the battery (in FuelTech’s case, it's mentioned multiple times), there is a high chance of issues if this isn’t followed. We had a recent case with a setup designed to swap between different ECUs for testing and learning purposes. The harness was a well-made, motorsport-grade harness with all best practices followed precisely. The car ran successfully on multiple ECUs with zero issues. However, as soon as the FuelTech was plugged in, it wouldn’t start. It had persistent trigger issues, and even when it did run, it wouldn’t last long. I temporarily ran cables directly from the ECU to the battery, and all the issues disappeared.

I’ve also seen other budget-level ECUs recommend wiring both positive and negative directly to the battery, with no isolators or battery kill switches. In one case, I discovered that if battery power was lost, all maps and tuning data were lost as well. Personally, I believe that ECU brands which require direct battery wiring are likely using lower-quality hardware than what’s found in higher-end ECUs. This makes them more susceptible to noise and signal degradation.

In short, if the manual stresses that the cables need to be run directly to the battery like your life depends on it, it's probably best to follow that advice. Otherwise, follow best practices and you shouldn't have any issues.