Isuzu KB P190. Manual - part 331

6E-290  Engine Control System (4JH1) 

Low Pressure Fuel Circuit Description 

 

 
 

 

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 1. Fuel 

Suction 

 2. Regulating 

Valve 

 3. Overflow 

Valve 

 4. Feed 

Pump 

  5.  To Fuel Tank 

 

The low pressure fuel circuit must supply sufficient fuel
to the high pressure fuel circuit. The main components
are the feed pump, the regulating valve and the
overflow valve. 
 
Feed Pump 

 

 

 

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 1. Rotor 

 2. Casing 

Ring 

 3. Fuel 

Supply 

 4. Outlet 

 5. Chamber 

 

 

 6. Vane 

 7. Driveshaft 

 8. Inlet 

 9. Fuel 

Suction 

 

The feed pump is driven by the drive shaft, performs 
suction and supply of fuel. The vanes assembled in the
rotor are pressed against the inside of the casing ring
by spring forces and centrifugal force during rotation to 
form chambers. When the vanes rotate, the volume of 
these chambers increase when they reach recesses the 
casing ring connected to the inlet port. Pressure then 
decreases and fuel is drawn in. When the chambers 
have passed the inlets and recesses, the volume
decreases and the fuel is compressed. Fuel pressure
increases until the chamber reaches the outlet, where 
the fuel passes through the regulating valve to the high 
pressure fuel circuit. 
 
Regulating Valve 

 

 

 

 

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 1. To 

Inlet 

 2. Spring 

 3. Valve 

Piston 

 4. Port 

 5. From 

Outlet 

 

When feed pump speed increases so that the delivery
pressure of the fuel delivered from the outlet exceeds 
the regulating valve spring force, the plunger is pushed
upwards. Excess fuel passes through the ports and 
returns to the inlet side, and the delivery pressure is
maintained within a specified range. When feed pump 
speed decreases so that the delivery pressure
decreases, the plunger is pushed downwards by spring 
force to close the port. 
 
 

Engine Control System (4JH1)  6E-291 

 

Overflow Valve 

 

 

 

 

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 1. Valve 

Holder 

 2. Port 

  3.  To Fuel Tank 

 4. Orifice 

Port 

  5.  From Fuel Tank 

 6. Ball 

Valve 

 7. Spring 

 

 

When the pressure of the fuel, returned from the
distributor head, exceeds the spring force, the overflow 
valve's ball valve is pushed up. Excess fuel presses 
through the port and returns to the tank, and fuel
pressure inside the pump chamber does not exceed a
specified pressure. The flow of excess fuel serves
cooling and automatic bleeding of the fuel pump during
operation. Also the orifice port is installed to assist in
automatic air bleeding. 

 

 

High Pressure Fuel Circuit Description 

 

 

 

 

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  1.  Fuel Injection Pump Control Unit (PCU) 

 2. Distributor 

Head 

  3.  Fuel Injection Solenoid Valve 

  4.  Constant Pressure Valve (CPV) 

 5. Radial 

Plunger 

 

In addition high pressure generating device, the high
pressure circuit also consists of fuel piping, and devices 
to set the beginning of injection and fuel injection
quantity. The main components are as follows: 

•  High pressure generation: Radial Plunger  
•  Fuel distribution: Distributor Head 
•  Beginning of injection timing: Timing Device 
• Prevention of secondary injection: Constant 

Pressure Valve (CPV) 

 

6E-292  Engine Control System (4JH1) 

Radial Plunger 

 

 
 

 

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 1. Radial 

Plunger 

 2. Internal 

Cam 

 3. Cam 

Ring 

 4. Rotor 

Shaft 

 5. Plunger 

Chamber 

 6. Roller 

Shoe 

 7. Roller 

 

While the radial plungers assembled to the rotor shaft
rotate, they are held against the inside of the cam ring 
(via the roller shoes and rollers) by fuel delivery
pressure from the feed pump and centrifugal force. The 
radial plungers perform rotational movement as well as
internal cam induced reciprocating movement to suck in
and compress the fuel in the plunger chamber. 
 

 

Distributor Head 

 

 

 

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 1. Rotor 

Shaft 

 2. Valve 

Needle 

  3.  Constant Pressure Valve (CPV) Holder 

  4.  High Pressure Outlet 

 5. Distributor 

Shaft 

 6. Barrel 

 

The distributor head distribute the high pressure fuel
that has flowed through the rotating rotor shaft's
distributor slits and the barrel's high pressure outlets (4
cylinders: 4) to the engine cylinders via the constant 
pressure valve (CPV) and the nozzle holder
assemblies. The fuel injection solenoid valve needle 
changes the passage to the radial plunger high 
pressure pump between fuel suction and fuel 
compression. 

Engine Control System (4JH1)  6E-293 

Fuel Injection Solenoid Valve 

 

 

 

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 1. Valve 

Seat 

  2.  Valve Closing Direction 

 3. Valve 

Needle 

 4. Coil 

 5. Magnet 

 6. Magnet 

Anchor 

 7. Rotor 

Shaft 

 

The fuel injection solenoid valve consists of a valve
seat, a valve needle, and a magnet anchor (a movable 
iron core), a coil and a magnet. The valve needle
rotates together with the rotor shaft. When current
controlled by the fuel injection pump control unit (PCU)
flows to the coil, the magnet anchor and the valve 
needle are pushed towards the valve seat. When the 
valve seat is completely closed by the valve needle, the
fuel in the high pressure passage is isolated from the
low pressure passage, is compressed by the radial
plunger high pressure pump, and injected into the
engine cylinder through the nozzle holder assembly.
When the required injection quantity is reached, the
current to the coil is cut, the valve seat opens and
injection of fuel is completed. 
 

 

 

Constant Pressure Valve (CPV) 
 

 
 
 

 

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 1. Plug 

 2. Ball 

 3. Seat 

 4. Valve 

 

 5. Spacer 

 6. Holder 

 7. Valve 

Spring 

 8. Oriffice 

 9. Ball 

Support 

 10.  Spring 

 

The constant pressure valve (CPV) consists of a holder, 
a spacer, a valve spring, a valve, a seat, a ball, a ball 
support, a spring and a plug. The valve is equipped with 
an orifice to suppress the reflected pressure wave (the
cause of secondary injection) caused by nozzle closing 
at the end of the injection and maintains a stable 
pressure in the injection pipe (residual pressure) to 
ensure stabilized injection timing for subsequent
injection. The valve is opened by pressurized fuel and 
this high pressure fuel is delivered to the nozzle holder
assembly.