Hi I have a 91 fleetwood that has been running bad intermittently for a while. It has been stumbling and backfiring under light throttle. Yesterday it started running really bad and quit running altogether. Now it will turn over but not start and the code 31 trouble code comes up(map sensor short). I took the sensor to auto zone and they checked it and said it was fine. So far I have changed the fuel pump, all the filters, and the spark plugs. The engine turns but it is acting like it is not getting fuel. Does anyone have any idea of what could be wrong? Any help would be greatly appreciated.