The speed advance device (Figure 4-58) is used to achieve best engine performance through the operating speed range of the engine. Timing advance is needed to compensate for the two delay periods: 1) the injection pressure wave traveling the length of the injection line, 2) the ignition delay period. The injection timing advance system controls… Read More »
All Stanadyne Diesel Systems DB2 Automotive pumps are equipped with electrical shut-off solenoids. (Figure 4-57). Illustrated here is an energized to run solenoid. When this is de-energized, an arm on the solenoid is moved out by spring force and physically closes the metering valve. This action interrupts injection, and stops the engine.
The return oil system (Figure 4-55) performs the following functions. 1.) A controlled flow through the housing maintains stable conditions for the internal parts. 2.) The fuel flow cools and lubricates the pump. 3.) It provides automatic air venting of the system. The return oil vent passage is fed, from the transfer pressure annulus. Fuel… Read More »
Another unique and very simple feature of the DB2 automotive pump is a viscosity compensating device. This component ensures proper transfer pump pressure regardless of the ambient temperature or grade of fuel used. (Figure 4-51). When fuel “ thins” out due to heat, pressure loss will occur. The thin fuel, however, permits increased leakage past… Read More »
In order to understand how designed fuel pressures are maintained over a broad range of conditions we’ll now take a closer look at regulator assembly operation. This illustration shows the operation of the pressure regulator assembly while the pump is running. Fuel output from the discharge side of transfer pump forces the piston in the… Read More »
Now for a closer look at some of the systems and components mentioned earlier in the program. Where model year design differences exist they will also be pointed out. Let’s begin with the component that supplies and pressurizes the fuel: The Transfer Pump. The positive displacement vane type transfer pump consists of a stationary liner… Read More »
While the discharge port is open, the movement of the rotor causes the rollers to contact the cam lobes, forcing the plungers together. The fuel is thus pressurized until the rollers pass over the top of the injection cam, when the pressure starts to drop. (Figure 4-43). The fuel then flows through the discharge outlet… Read More »
As the rotor revolves, the two rotor inlet passages register with charging ports in the hydraulic head. (Figure 4-40). This allows fuel to flow into the pumping chamber. (Figure 4-41). For improved roller retention, the 6.2L engine will use a new roller shoe. It will provide increased shoe wrap-around by positioning the roller deeper into… Read More »
The general operating principal of the pump may be easily understood by following the fuel circuit through the pump. FUEL FLOW First, the fuel is drawn into the pump inlet, and through the inlet filter screen by the transfer pump. Excess fuel is bypassed through the pressure regulator assembly, and back through the suction side.… Read More »
The main rotating components (Figure 4-32) are the drive shaft, the distributor rotor, the transfer pump blades and the governor. The drive shaft engages the distributor rotor in the hydraulic head. The drive end of the rotor incorporates two pumping plungers. The plungers are actuated toward each other simultaneously by an internal cam ring through… Read More »