If they put a fuel pressure gauge on the fuel rail (I just clamped a hose onto the outside of the schrader valve, after unscrewing the stem of the valve) they will be able to see if the regulator is working. It lets the pressure go up and down as you push on the gas. A stab on the gas pedal and the pressure should shoot upward, from maybe 30 psi to 36 or so. I think it sits at about 28 psi when idling.
You might want to do a search in the forums for something like 'poor gas mileage' or 'bad mpg', etc. It can have causes like a bad temperature sensor, a vacuum leak, an injector that is stuck, a bad oxygen sensor, and others. We had poor gas mileage (32 miles per gallon on the highway instead of 37 mpg) when the front brake calipers were not sliding across to compensate for pad wear. One side of the pads was wearing away fairly quickly, and the drag was causing poor mileage. Bad plugs will lower mpg also.