munipulate sensor signal by increasing voltage - car

There is a very handy opamp circuit called a subtractor, that outputs the difference of two voltages, but with the result referenced to an arbitrary third voltage. See page 6 of:

You would connect ground to V1, the ECU signal to V2 (so the subtractor would subtract zero from the ECU signal, and connect a .65 volt reference voltage instead of ground to the right side of RF. This adds .65 to the difference of V2 - V1. You will have to come up with a stable .65 volt reference. Perhaps a forward biased diode is stable enough. Or you might use an integrated reference chip, like an LMV431:

I think an LM358 dual opamp would work for this application.

Of course, you have to work out the power supply requirements for these components, in your environment.

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Thank you for the response. I looked at the OP-AMP subtractor / adder. Not having any electronic knowledge, I don't understand RF resistor requirement, or any of the resistors requirements.

I found this searching on terms in your reply:

Seem to be a little closer or same thing with changes you suggested.

But what determinds what resistors go where?

Thanks, Rey