15.2 Trouble Shooting Engine
DETROIT DIESEL 53
2. Remove the fuel strainer shell and element from the
pressures between cylinders must not exceed 25 psi at
strainer cover and fill the shell with fuel oil. Install the
600 rpm.
shell and element.
EXAMPLE:
If the compression
pressure readings were as shown in
3. Remove and fill the fuel filter shell and element with
the following table, it would be
fuel oil as in Step 2.
evident that No. 3 cylinder should be
examined and the cause of the low
4. Start the engine. Check the filter and strainer for
compression pressure be determined
leaks.
and corrected.
NOTE: In some instances, it may be
Cylinder
Gage Reading*
necessary to remove a valve rocker
1
525 psi
cover and loosen a fuel pipe nut in
2
520 psi
order to bleed trapped air from the
3
485 psi
fuel system. Be sure the fuel pipe is
4
515 psi
retightened securely before replacing
the rocker cover.
The above pressures are for an engine operating at an
altitude near sea level.
Primer J 5956 may be used to prime the entire fuel
system. Remove the filler plug in the fuel filter cover
Note that all of the cylinder pressures are above the low
and install the primer. Prime the system. Remove the
limit for satisfactory engine operation. Nevertheless, the
primer and install the filler plug.
No. 3 cylinder compression pressure indicates that
Fuel Flow Test
something unusual has occurred and that a localized
1. Disconnect the fuel return hose and hold the open
pressure leak has developed.
end in a suitable container.
Low cylinder pressure may result from any one of
2. Start and run the engine at approximately 1200 rpm
several causes:
and measure the fuel flow from the return hose for one
minute. At least 0.6 gallon of fuel should flow from the
A.
Piston rings may be stuck or broken. To
return hose per minute.
determine the condition of the rings, remove the
air box cover and inspect them by pressing on
3. Be sure all of the connections between the fuel
the rings with a blunt tool. A broken or stuck
supply and the pump are tight so that no air will be
ring will not have a "springlike" action.
drawn into the fuel system; then, immerse the end of the
B.
Compression pressure may be leaking past the
fuel hose in the fuel in the container. Air bubbles rising
cylinder head gasket, the valve seats, the
to the surface of the fuel will indicate a leak on the
injector tube, or a hole in the piston.
suction side of the pump.
Crankcase Pressure
Engine Out of Fuel
The crankcase pressure indicates the amount of air that
has passed between the oil control rings and the
The problem in restarting the engine after it has run out
cylinder liner into the crankcase, most of which is clean
of fuel stems from the fact that after the fuel is
air from the air box. A slight pressure in the crankcase
exhausted from the fuel tank, fuel is then pumped from
is desirable to prevent the entrance of dust. A loss of
the primary fuel strainer and sometimes partially
engine lubricating oil through the breather tube,
removed from the secondary fuel filter before the fuel
crankcase ventilator, or dipstick hole in the cylinder
supply becomes insufficient to sustain engine firing.
block is indicative of excessive crankcase pressure.
Consequently, these components must be refilled with
The causes of high crankcase pressure may be traced
fuel and the fuel pipes rid of air in order for the system
to excessive blow-by due to worn piston rings, a hole or
to provide adequate fuel for the injectors.
crack in a piston crown, loose piston pin retainers, worn
blower oil seals, defective blower, cylinder, or end plate
When an engine has run out of fuel, there is a definite
gaskets, or excessive exhaust back pressure. Also, the
procedure to follow for restarting it: 1. Fill the fuel tank
breather tube or crankcase ventilator should be checked
with the recommended grade of fuel oil. If only partial
for obstructions.
filling of the tank is possible, add a minimum of ten
gallons of fuel.
1970 General Motor Corp
Page 2
