DIRT IN FUEL SYSTEM
engine operating troubles result directly or indirectly from dirt in the fuel system. That
is why proper fuel storage and handling are so important. One of the most important
aspects of diesel fuel is cleanliness. The fuel should not contain more than a trace of
foreign substance; otherwise, fuel pump and injector troubles will occur. Diesel fuel,
because it is more viscous than gasoline, will hold dirt in suspension for longer periods.
Therefore, every precaution should be made to keep the fuel clean.
If the engine
starts missing, running irregularly, rapping, or puffing black smoke from the exhaust
manifold, look for trouble at the spray nozzle valves. In this event, it is almost a sure
bet that dirt is responsible for improper fuel injection into the cylinder. A valve held
open or scratched by particles of dirt so that it cannot seat properly will allow fuel to
pass into the exhaust without being completely burned, causing black smoke. Too much fuel
may cause a cylinder to miss entirely. If dirt prevents the proper amount of fuel from
entering the cylinders by restricting spray nozzle holes, the engine may skip or stop
entirely. In most cases, injector or valve troubles are easily identified.
injection pump operation, however, is not easily recognized It is more likely caused by
excessive wear than by an accumulation of dirt or carbon, such as the spray nozzle is
subjected to it in the cylinder combustion chambers. If considerable abrasive dirt gets by
the filters to increase (by wear) the small clearance between the injector pump plunger
and barrel, fuel will leak by the plunger instead of being forced into the injector nozzle
in the cylinder. This gradual decrease in fuel delivery at the spray nozzle may remain
unnoticed for some time or until the operator complains of sluggish engine performance.
worn injector pumps will result in loss of engine power and hard starting, worn piston
rings, cylinder liners, and valves (intake and exhaust) can be responsible for the same
conditions. However, with worn cylinder parts or valves, poor compression, a smoky
exhaust, and excessive blow-by will accompany the hard starting and loss of power from the