DETROIT DIESEL 53
Shop Notes 2.0
LOCATING AIR LEAKS IN FUEL LINES
Air drawn into the fuel system may result in uneven running of the engine, stalling when idling, or a loss of
power. Poor engine operation is particularly noticeable at the lower engine speeds. An opening in the fuel
suction lines may be too small for fuel to pass through but may allow appreciable quantities of air to enter.
Check for loose or faulty connections. Also check for improper fuel line connections such as a fuel pump
suction line connected to the short fuel return tube in the fuel tank which would cause the pump to draw air.
Presence of an air leak may be detected by observation of the fuel filter contents after the filter is bled and the
engine is operated for 15 to 20 minutes at a fairly high speed. No leak is indicated if the filter shell is full when
loosened from its cover. If the filter shell is only partly full, an air leak is indicated.
Flexible fuel lines are used in certain applications to facilitate connection of lines leading to and from the fuel
tank, and to minimize the effects of any vibration in the installation.
Be sure a restricted fitting of the proper size is used to connect the fuel return line to the fuel return manifold.
Do not use restricted fittings anywhere else in the fuel system.
When installing fuel lines, it is recommended that connections be tightened only sufficiently to prevent leakage
of fuel; thus flared ends of the fuel lines will not become twisted or fractured because of excessive tightening.
After all fuel lines are installed, the engine should be run long enough to determine whether or not all
connections are sufficiently tight. If any leaks occur, connections should be tightened only enough to stop the
leak. Also check filter cover bolts for tightness.
August, 1972 SEC. 2.0