Was 12v just used for convenience, or was it needed because the ECU checks the valve is floating up to 12v in between pulses or something?

Likely would work with nothing as a pull up but I don't like things to just float. I had a pin out for the connector at one point but it went with an engine I had sold.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10