DETROIT DIESEL UNIT INJECTION
system used by Detroit diesel is known as a low-pressure fuel system, owing to the fact
that fuel delivered to the unit injectors averages 45 to 70 psi.
This is much
lower than the average 2,500 to 300 psi that passes through the fuel line from the
injection pump and nozzles used in other systems.
The four main
functions of the fuel system used with a Detroit diesel engine are as follows:
supply clean, cool fuel to the system by passing it through at least a primary and
secondary filter before the pump and injectors.
cool and lubricate the injectors, as the fuel flows through them, and return to the tank
maintain sufficient pressure at all times through the action of the positive displacement
gear pump and the use of a restricted fitting located at the cylinder head return fuel
purge the fuel system of any air; the system is recirculator-y in operation, therefore
allowing any air to be returned to the fuel tank.
basic fuel system used on all Detroit diesel engines is identical as far as components
used, the description of operation for one can be readily related to any other series of
Detroit diesel engine (fig. 5-23).
The basic fuel
system consists mainly of the following:
pipes to and from the injectors (inlet and outlet).
manifolds, which are cast internally within the cylinder head. The upper manifold is the
"inlet" and the lower is the "return" or "outlet." To
prevent confusion, the words in and out are cast in the side of the head.
pump (supply pump, not an injection pump).
strainer or primary filter.
fitting on in-line engines or a restricted TEE on V-type engines.
5-23.Diagram of typical Detroit diesel fuel system.