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ECU grounding

EFI Wiring Fundamentals

Relevant Module: EFI Wiring Harness Design > Power Grounding > Star Point Earthing

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Dear HP academy ,

you mentioned that the best point to ground the wires is to the engine block, but im concerned about the ecu grounding , as i found this article ( Grounding the ECU directly to the engine block during cranking can cause voltage drops and induce currents that may damage the ECU. It is generally recommended to ground the ECU directly to the battery or a common ground point, rather than the engine block or chassis ground. This helps to avoid voltage drops and ensure that the ECU receives a stable and reliable ground reference )

so if im grounding the ecu to the engine block, during cranking there will be voltage drop , and the ecu may have un accurate reading due to voltage drop and may be damaged , in other hand , if i ground the ecu to the battery , the ecu may not have the same ground reading as all the sensors that is grounded to the engine block , pleas help me as im confused

thank you .

A couple things.

While the theory that a current could be induced through the ground wires of the ECU when grounded to the engine is a plausible theory, a lot of things would have to go wrong in order for that to happen. Many OEMs ground their ECU/ECM/PCMs directly to the engine, typically one of the heads, occasionally bellhousing bolts. I've been working with automotive electrical for a few decades now and have yet to see a scenario happen where grounding the ECU to the engine was the cause of ECU damage. The only acceptable ECU ground points are the engine itself an the battery itself.

About your sensor offset issue, that should never be an issue regardless of where the ECU main (power) ground is, because the sensor grounds should all be grounded to the sensor ground terminal(s) of the ECU itself, so that the reference is maintained for all sensors under all conditions.

I'll second what Chris said. I can't think of an OEM vehicle newer then 1990 that doesn't ground the ECU to the head or block.

Haltech has a good article on this, with pictures.

In my opinion if the voltage drop between the battery and block is so large that it causes an issue, you have a problem with the electrical system as a whole (starter power too small, bad battery, poor connections, dirty or no grounds, etc etc). Grounding to the battery is a common recommendation it seems with lower tier ECU manufacturers, it does simplify install and is kind of a short cut around the rest of the electrical system being healthy and installed properly.

Star point grounding is the method of choice, the haltech article has some good explanations for why the block is most often the star point. Especially 3 pin coils need the ground plane to the same as the ecu, and to keep the ground loop small and EMI down the ignition coils get grounded to the head and therefore so does the ECU.

There isn't 100% a one size fits all solution for everything but 90% of installs can follow star point grounding with no issues.

If the battery is nearby, connecting the negative battery terminal to your engine ground point is an easy way to avoid your main concern, and as Six_Shooter correctly pointed out, the purpose of the sensor ground wiring is to avoid the offset you described since your sensors are receiving their ground from the ECU.

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