COVER GP-VALVE MECHANISM 4W2172 - Caterpillar

The FRC fuel position is a limit that is based on boost pressure in order to control the fuel air mixture for the emission control. When the ECM senses an increase in the boost pressure, the ECM increases the FRC fuel position. The rated fuel position is a limit that is based on the horsepower rating of the engine. The rated fuel position is similar to the rack stops and the torque spring on a mechanically governed engine. The rated fuel position provides the horsepower and the torque curves for a specific engine family. The rated fuel position provides the horsepower and the torque curves for a specific horsepower rating. The limits are programmed by the factory into the personality module. The limits are not programmable in the field.The injection timing relies on the following engine parameters: engine speed, engine load and other engine data. The ECM senses the top center position of number one cylinder from the signal that is provided by the engine speed/timing sensors. The ECM decides when the injection should occur relative to this top center position. The ECM provides the signal to the unit injector at the desired time.Unit Injector Mechanism
Illustration 2 g01430766
Typical unit injector mechanism
(17) Unit injector
(18) Adjusting nut
(19) Rocker arm assembly
(20) Camshaft The unit injector mechanism provides the downward force that is required to pressurize the fuel in the unit injector. When a signal is received from the ECM, the unit injector (17) injects the pressurized fuel into the combustion chamber. The camshaft gear is driven by an idler gear which is driven through the front gear train by the crankshaft gear. The gears of the front gear train that are timed must be aligned in order to provide the correct relationship between the piston and valve movement. During assembly of the front gear train, care must be taken in order to correctly align the timing marks of the gears. The camshaft has three camshaft lobes for each cylinder. Two lobes operate the inlet and exhaust valves, and one operates the unit injector mechanism. Force is transferred from the unit injector lobe on camshaft (20) through rocker arm assembly (19) to the top of the unit injector. The adjusting nut (18) allows setting of the unit injector adjustment. Refer to the section on adjustment of the injector in Testing and Adjusting for the proper setting of the unit injector.Unit Injector
Illustration 3 g01332439
(21) Solenoid
(22) Tappet
(23) Plunger
(24) Barrel
(25) Nozzle assembly Operation of the Electronic Unit Injector
The operation of the Electronic Control Unit (EUI) consists of the following four stages: Pre-injection, Injection, End of injection and Fill. Unit injectors use a plunger and barrel to pump high pressure fuel into the combustion chamber. Components of the injector include the tappet, the plunger, the barrel and nozzle assembly. Components of the nozzle assembly include the spring, the nozzle check, and a nozzle tip. The cartridge valve is made up of the following components: solenoid, armature, poppet valve and poppet spring.The injector is mounted in an injector