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Knock sensor shield grounding

EFI Wiring Fundamentals

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I am used to wiring Link ECUs where the wiring instructions would say to ground the shield to sensor ground.

I have recently worked on a Syvecs ECU and after talking to technical support (and also as per the wiring instructions), I was recommended to ground the shield to power ground instead of knock sensor ground.

What's the difference between the two and why is it different for different ECUs?

There is no golden rule, it will mostly come down to the hardware design, so you should always follow the manufacturer's advice if it is given. The object is to drain any current that is radiated into the shield to ground (0V), with most systems there is a strong path to ground either via sensor ground or chassis ground so either will do. With some systems there is not - in Syvecs and Life Im pretty sure the sensor ground is completely isolated and has over current protection etc.

In the case of hardware where the grounds arent isolated, some may work on the theory that it is better to dump that energy to chassis ground so it doesn't influence your sensor ground, others work on the theory that by connecting the shield to the noisy chassis ground you are encasing the sensitive signal wires with a potentially noisy shield. In reality, the energy that is passing through the shield is so highly attenuated that either is totally fine.

Thank you Adam, very clear explanation.

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