FUEL DRAIN TUBES
DESCRIPTION
These rubber tubes are low–pressure type. Some
fuel is continually being returned to the fuel injection
pump. During injection, a small amount of fuel flows
past the injector needle and is not injected into the
combustion chamber. This cools and lubricates the
injectors. This fuel flows through the fuel drain tubes
(Fig. 7) and back to the tee banjo fitting, which is
connected to the same line as the overflow valve. The
overflow valve is calibrated to open at a preset pres-
sure. Excess fuel not required by the pump to main-
tain the minimum pump cavity pressure is then
returned through the overflow valve and on to the
fuel tank through the fuel return line.
FUEL HEATER
DESCRIPTION
The fuel heater is used to prevent diesel fuel from
waxing and plugging the fuel filter during cold
weather operation. The fuel heater is located in the
bottom plastic bowl of the fuel filter/water separator
(Fig. 8).
The element inside the heater assembly is made of
a Positive Temperature Coefficient (PTC) material,
and has power applied to it by the fuel heater relay
anytime the ignition key is in the “on” position. PTC
material has a high resistance to current flow when
its temperature is high, which means that it will not
generate heat when the temperature is above a cer-
tain value. When the temperature is below 7°C (45°
F), the resistance of the PTC element is lowered, and
allows current to flow through the fuel heater ele-
ment warming the fuel. When the temperature is
above 29°C (85° F), the PTC element’s resistance
rises, and current flow through the heater element
stops.
Voltage to operate the fuel heater is supplied from
the ignition (key) switch and through the fuel heater
relay. Refer to the following Fuel Heater Relay for
additional information. The fuel heater and fuel
heater relay are not controlled by the Power-
train Control Module (PCM).
FUEL HEATER RELAY
DESCRIPTION
Voltage to operate the fuel heater is supplied from
the ignition (key) switch through the fuel heater
relay. The PCM or ECM is not used to control
this relay.
The fuel heater relay is located in the PDC. The
PDC is located next to the battery in the engine com-
partment. For the location of the relay within the
PDC, refer to label on PDC cover.
DIAGNOSIS AND TESTING
GENERAL INFORMATION
This section of the group will cover a general diag-
nosis of diesel engine fuel system components.
Diagnostic Trouble Codes: Refer to On-Board
Diagnostics in Group 25, Emission Control System
for a list of Diagnostic Trouble Codes (DTC’s) for cer-
tain fuel system components.
VISUAL INSPECTION
A visual inspection for loose, disconnected, or incor-
rectly routed wires and hoses should be made before
attempting to diagnose or service the diesel fuel
injection system. A visual check will help find these
conditions. It also saves unnecessary test and diag-
nostic time. A thorough visual inspection of the fuel
injection system includes the following checks:
Fig. 7 Fuel Drain Tubes
Fig. 8 Fuel Heater Temperature Sensor and Element
Location
1 – TERMINAL 2
2 – FUEL HEATER
3 – TERMINAL 1
14 - 6
FUEL SYSTEM—2.5L DIESEL ENGINE
XJ
DESCRIPTION AND OPERATION (Continued)
2000 JEEP CHEROKEE