What was found
A MECHANIC WAS PERFORMING MX RUN-UP ON A STRAIGHT NAVAJO, WHEN BOTH ENGINES QUIT DUE TO FUEL STARVATION. PRIOR TO THE RUN, HE HAD CHECKED FUEL QUANTITY INDICATORS, WHICH SHOWED ONE-FOURTH TANK IN EACH MAIN TANK. THE MAIN (INBOARD) TANK HAS 2 SENDERS, AN INBOARD (40648-03) AND AN OUTBOARD (40648-02); INBOARD SENDER IS LONGER THAN OUTBOARD. INVESTIGATION SHOWED THAT IN THIS ACFT, THE 2 SENDERS HAD BEEN SWITCHED. WHEN LONGER SENDER IS PUT IN OUTBOARD LOCATION, IT WILL HIT BOTTOM OF TANK, GIVING A FALSE ONE-FOURTH FULL INDICATION. THIS IS SECOND TIME THIS CONDITION HAS BEEN FOUND IN THE LAST 6 WEEKS. WHILE BOTH INCIDENTS INVOLVED 31-310'S, PARTS, & POTENTIAL FOR PROBLEM, IS SAME IN PA31350 CHIEFTANS.