Testing in Fuel Ingection System section of this
group for test procedures.
FUEL INJECTOR TEST
The fuel injection nozzels, located in the engine
cylinder head, spray fuel under high pressure into
the individual combustion chambers. Pressurized
fuel, delivered by the fuel injection pump, unseats a
spring-loaded needle valve inside the injector, and
the fuel is atomized as it escapes through the injector
opening into the engine’s combustion chamber. If the
fuel injector does not operate properly, the engine
may misfire, or cause other driveability problems.
A leak in the injection pump–to–injector high–pres-
sure fuel line can cause many of the same symptoms
as a malfunctioning injector. Inspect for a leak in the
high–pressure lines before checking for a malfunc-
tioning fuel injector.
WARNING: THE INJECTION PUMP SUPPLIES HIGH-
–PRESSURE FUEL OF UP TO APPROXIMATELY
45,000 KPA (6526 PSI) TO EACH INDIVIDUAL INJEC-
TOR THROUGH THE HIGH–PRESSURE LINES. FUEL
UNDER THIS AMOUNT OF PRESSURE CAN PENE-
TRATE THE SKIN AND CAUSE PERSONAL INJURY.
WEAR SAFETY GOGGLES AND ADEQUATE PRO-
TECTIVE CLOTHING. AVOID CONTACT WITH FUEL
SPRAY WHEN BLEEDING HIGH–PRESSURE FUEL
LINES.
WARNING: DO NOT BLEED AIR FROM THE FUEL
SYSTEM OF A HOT ENGINE. DO NOT ALLOW FUEL
TO SPRAY ONTO THE EXHAUST MANIFOLD WHEN
BLEEDING AIR FROM THE FUEL SYSTEM.
To determine which fuel injector is malfunctioning,
run the engine and loosen the high–pressure fuel line
nut at the injector (Fig. 18). Listen for a change in
engine speed. If engine speed drops, the injector was
operating normally. If engine speed remains the
same, the injector may be malfunctioning. After test-
ing, tighten the line nut to 19 N·m (14 ft. lbs.)
torque. Test all injectors in the same manner one at
a time.
Once an injector has been found to be malfunction-
ing, remove it from the engine and test it. Refer to
the Removal/Installation section of this group for pro-
cedures.
After the injector has been removed, install it to a
bench–mount
injector
tester.
Refer
to
operating
instructions supplied with tester for procedures.
The opening pressure or “pop” pressure should be
15,000–15,800 kPa (2175–2291 psi). If the fuel injec-
tor needle valve is opening (“popping”) to early or to
late, replace the injector.
FUEL INJECTOR / NEEDLE MOVEMENT
SENSOR TEST
The needle movement sensor is used only on the
number–1 cylinder fuel injector (Fig. 19). It is not
used on the injectors for cylinders number 2, 3, or 4.
Testing the needle movement sensor requires the
use of a DRB Scan tool. Refer to the Powertrain
Diagnostic Procedures manual for additional infor-
mation.
FUEL INJECTION PUMP TEST
The injection pump is not to be serviced or
the warranty may be voided. If the injection
pump requires service, the complete assembly
must be replaced.
Incorrect injection pump timing (mechanical or
electrical) can cause poor performance, excessive
smoke and emissions and poor fuel economy.
A defective fuel injection pump, defective fuel tim-
ing solenoid or misadjusted mechanical pump timing
can cause starting problems or prevent the engine
from revving up. It can also cause:
• Engine surge at idle
• Rough idle (warm engine)
• Low power
• Excessive fuel consumption
• Poor performance
• Low power
Fig. 18 Typical Inspection of Fuel Injector
1 – FUEL INJECTOR
2 – LINE FITTING
3 – HIGH-PRESSURE FUEL LINE
4 – FUEL DRAIN TUBES
14 - 10
FUEL SYSTEM—2.5L DIESEL ENGINE
XJ
DIAGNOSIS AND TESTING (Continued)
2000 JEEP CHEROKEE