You definitely want the ECU to be grounded properly.
Some of the ECU'S are painted front and back. Take a screwdriver and scrape the paint off the 2 bolt mounting areas on the back of the ECU. And then, take the same screw driver and scrape the paint off the car where the ECU mounts. Only scrape the paint off the car where the ECU will cover.
This will give you a nice ground.
On my slant car, I added a ground jumper wire, for a good ground.
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