My friend has a 1995 Ford F-150 with dual tanks. Front tank hasn't worked since he's had it. It would not start or run on the front tank. Today I played with it and for no apparent reason it fired right up on the front tank. I could hear the pump running and it had pressure at the rail. Put a few gallons of gas in it and it drove for a few miles on the front tank then died. I ran the obd 1 scanner on it and got code 542. Any ideas on what it could be?