Interesting on the codes. Not sure what that means. And, I'm no help on the voltage to the sensors. I do know the DME sends a 5v DC signal to the AFM...not sure about the rest of the sensors.
Slight surge? Hmmm...how old's the O2 sensor? Just for grins, you might try running the car in open loop (O2 sensor disconneced) and see what that does.
For about $20, you can buy a high pressure fuel gauge from Summitt Racing. Go to a local hotrod shop and for another $10 or so you can get a "T" and tap it into your fuel like under the intake manifold. The problem will likely be trying to observe the gauge at your 50-70 MPH speed.
Curious issue...
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy