I'm trying to replicate the voltages coming from an accelerator pedal, to the ECM, on 6.0 L Diesel engine. I acquired the three separate voltages using an oscilloscope. I have access to two analog output channels on the dyno. Out of the three voltages two them follow each other by a difference of 0.6 volts. Going from 1.58 to 4.26 and 1.00 to 3.64, equating to 0 to 100% throttle. I have uploaded the current schematic I'm trying to utilize to achieve this goal. V1 will always be 12v and V2 will be an analog output, going from 1.58 to 4.26. My original schematic was only utilizing one op amp as a differential amplifier, but the V-(pin 2 of U2A) was rising with V+. I was not getting a constant 0.6v difference between the two signals. So I then added two voltage follower circuits, as shown, to buffer the signals going into U2A. If I run the current schematic in my simulation software, everything works out great. I get a liner voltage out at Probe1 rising from 1.00v to 3.64, which is what I'm looking for. When I build the schematic in real life and test it I am getting a more constant voltage difference, but I'm not able to dial it in precisely. After some trouble shooting I found that I'm not getting the same voltage in as I'm getting out on probe 3 and probe 4. Instead of going from .568 v to .568 v it goes .568 to .738v. I've tried surfing for half a day on a solution and I'm not getting anywhere. Any help would be appreciated. Thanks!