DETROIT DIESEL UNIT INJECTION SYSTEMS

The fuel 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:

1. To supply clean, cool fuel to the system by passing it through at least a primary and secondary filter before the pump and injectors.
2. To cool and lubricate the injectors, as the fuel flows through them, and return to the tank (recirculatory system).
3. To 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 manifold.
4. To 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.

Since the 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:

1. Fuel injectors.
2. Fuel pipes to and from the injectors (inlet and outlet).
3. Fuel 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.
4. Fuel pump (supply pump, not an injection pump).
5. Fuel strainer or primary filter.
6. Fuel filter (secondary).
7. Fuel lines.
8. One-way check valve.
9. Restricted fitting on in-line engines or a restricted TEE on V-type engines.