Gas Mileage

Stop on an incline, shift to neutral, release the brakes and see if it creeps downhill on its own. If not, suspect a dragging brake. Next, find a mechanic with a scanner that will read live sensor data and view the fuel trim numbers. If they are very high negative, the Engine Computer sees there is too much fuel going into the engine and trying to reduce the amount. If the numbers are very high positive, the computer is responding to incorrect sensor information and is adding fuel. If the van was hit hard enough, look for a kinked fuel return line from the fuel pressure regulator on the engine to the gas tank. That could allow fuel pressure to go too high which would result in too much fuel spraying in each time an injector opened.