Trouble Shooting
DETROIT DIESEL
from the primary fuel strainer and sometimes partially
connectors to permit fuel to flow directly to the fuel
removed from the secondary fuel filter before the fuel
return manifold.
supply becomes insufficient to sustain engine firing.
Consequently, these components must be refilled with
5. Start the engine and run it at 600 rpm. Observe and
fuel and the fuel pipes rid of air in order for the system
record the compression pressure indicated on the gage.
to provide adequate fuel for the injectors.
NOTE: Do not crank the engine with the
When an engine has run out of fuel, there is a definite
starting motor to check the compression
procedure to follow for restarting it. The procedure is
pressure.
outlined below:
6. Perform Steps 2 through 5 on each cylinder. The
1. Fill the fuel tank with the recommended grade of
compression pressure in any one cylinder should not be
fuel oil. If only partial filling of the tank is possible, add
less than 430 psi (540 psi for "N" engines) at 600 rpm.
a minimum of ten gallons of fuel.
In addition, the variation in compression pressures
2. Remove the fuel strainer shell and element from the
between cylinders of the engine must not exceed 25 psi
strainer cover and fill the shell with fuel oil. Install the
at 600 rpm.
shell and element.
3. Remove and fill the fuel filter shell and element with
EXAMPLE: If the compression pressure
fuel oil as in Step 2.
readings were as shown in Table 2, it would
4. Start the engine. Check the filter and strainer for
be evident that No. 3 cylinder should be
leaks.
examined and the cause of the low
compression pressure be determined and
NOTE: In some instances, it may be
corrected.
necessary to remove a valve rocker
cover and loosen a fuel pipe nut in order
Note that all of the cylinder pressures are above the low
to bleed trapped air from the fuel system.
limit for satisfactory engine operation. Nevertheless, the
Be sure the fuel pipe is retightened
No. 3 cylinder compression pressure indicates that
something unusual has occurred and that a localized
securely before replacing the rocker
pressure leak has developed.
cover.
Low compression pressure may result from any one of
Primer J 5956 may be used to prime the engine fuel
several causes:
system. Remove the filler plug in the fuel filter cover
and install the primer. Prime the system. Remove the
A. Piston rings may be stuck or broken. To
primer and install the filler plug.
determine the condition of the rings, remove
the air box cover and press on the
Fuel Flow Test
compression rings with a blunt tool. A
broken or stuck compression ring will not
1. Disconnect the fuel return hose from the fitting at
have a "spring-like" action.
the fuel tank and hold the open end in a suitable
B. Compression pressure may be leaking past
container.
the cylinder head gasket, valve seats,
2. Start and run the engine at 1200 rpm and measure
injector tubes or through a hole in the
the fuel flow for a period of one minute. At least .6
piston.
gallon of fuel should flow from the fuel return hose per
minute.
Engine Out of Fuel
3. Immerse the end of the fuel return hose in the fuel
in the container. Air bubles rising to the surface of the
The problem in restarting the engine after it has run out
fuel will indicate air being drawn into the fuel system on
of fuel stems from the fact that after the fuel is
the suction side of the pump.
exhausted from the fuel tank, fuel is then pumped
If, air is present, tighten all feel line connections
Cylinder
Gage Reading*
between the fuel tank and the fuel pump.
1
525 psi
2
520 psi
If the fuel flow fails to meet the amount specified, the
3
485 psi
fuel strainer, filter or pump should be serviced.
4
515 psi
*The above pressures ore for an engine operating at on
altitude near sea level.
TABLE 2
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