Jeep XJ. Manual — part 286
CONDITION
POSSIBLE CAUSES
CORRECTION
LOW OIL PRESSURE
1. Low oil level
1. Check oil level and fill if
necessary
2. Faulty oil pressure sending unit
2. Install new sending unit
3. Clogged oil filter
3. Install new oil filter
4. Worn oil pump
4. Replace worn gears or oil pump
assy
5. Thin or diluted oil
5. Change oil to correct viscosity.
Refer to this group for correct
procedure/engine oil specifications
6. Excessive bearing clearance
6. Measure bearings for correct
clearance
7. Oil pump relief valve stuck
7. Remove valve to inspect, clean
and reinstall
8. Oil pump suction tube loose,
broken, bent or clogged
8. Inspect suction tube and clean or
replace if necessary
9. Oil pump cover warped or
cracked
9. Install new oil pump
OIL LEAKS
1. Misaligned or deteriorated
gaskets
1. Replace gasket
2. Loose fastener, broken or porous
metal part
2. Tighten, repair or replace the part
3. Front or rear crankshaft oil seal
leaking
3. Replace seal
4. Leaking oil gallery plug or cup
plug
4. Remove and reseal threaded
plug. Replace cup style plug
EXCESSIVE OIL CONSUMPTION
OR SPARK PLUGS OIL FOULED
1. PCV System malfunction
1. Refer to group 25, Emission
Control System for correct operation
2. Defective valve stem seal(s)
2. Repair or replace seal(s)
3. Worn or broken piston rings
3. Hone cylinder bores. Install new
rings
4. Scuffed pistons/cylinder walls
4. Hone cylinder bores and replace
pistons as required
5. Carbon in oil control ring groove
5. Remove rings and de-carbon
piston
6. Worn valve guides
6. Inspect/replace valve guides as
necessary
7. Piston rings fitted too tightly in
grooves
7. Remove rings and check ring end
gap and side clearance. Replace if
necessary
9 - 12
2.5L ENGINE
XJ
DIAGNOSIS AND TESTING (Continued)
INTAKE MANIFOLD LEAKAGE DIAGNOSIS
An intake manifold air leak is characterized by
lower than normal manifold vacuum. Also, one or
more cylinders may not be functioning.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR THE FAN.
DO NOT WEAR LOOSE CLOTHING.
(1) Start the engine.
(2) Spray a small stream of water at the suspected
leak area.
(3) If a change in RPM is observed the area of the
suspected leak has been found.
(4) Repair as required.
CYLINDER COMPRESSION PRESSURE TEST
The results of a cylinder compression pressure test
can be utilized to diagnose several engine malfunc-
tions.
Ensure the battery is completely charged and the
engine starter motor is in good operating condition.
Otherwise the indicated compression pressures may
not be valid for diagnosis purposes.
(1) Clean the spark plug recesses with compressed air.
(2) Remove the spark plugs.
(3) Secure the throttle in the wide-open position.
(4) Disable the fuel system. (Refer to Group 14,
Fuel System for the correct procedure)
(5) Disconnect the ignition coil.
(6) Insert a compression pressure gauge and rotate the
engine with the engine starter motor for three revolutions.
(7) Record the compression pressure on the 3rd revo-
lution. Continue the test for the remaining cylinders.
Refer to Engine Specifications for the correct
engine compression pressures.
ENGINE CYLINDER HEAD GASKET FAILURE
DIAGNOSIS
A leaking engine cylinder head gasket usually results
in loss of power, loss of coolant and engine misfiring.
An engine cylinder head gasket leak can be located
between adjacent cylinders or between a cylinder and
the adjacent water jacket.
• An engine cylinder head gasket leaking between
adjacent cylinders is indicated by a loss of power
and/or engine misfire.
• An engine cylinder head gasket leaking between
a cylinder and an adjacent water jacket is indicated
by coolant foaming or overheating and loss of coolant.
CYLINDER-TO-CYLINDER LEAKAGE TEST
To determine if an engine cylinder head gasket is
leaking between adjacent cylinders; follow the proce-
dures outlined in Cylinder Compression Pressure
Test. An engine cylinder head gasket leaking between
adjacent cylinders will result in approximately a
50-70% reduction in compression pressure.
CYLINDER-TO-WATER JACKET LEAKAGE TEST
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR THE FAN.
DO NOT WEAR LOOSE CLOTHING.
Remove the radiator cap.
Start the engine and allow it to warm up until the
engine thermostat opens.
If a large combustion/compression pressure leak
exists, bubbles will be visible in the coolant.
If bubbles are not visible, install a radiator pres-
sure tester and pressurize the coolant system.
If a cylinder is leaking combustion pressure into
the water jacket, the tester pointer will pulsate with
every combustion stroke of the cylinder.
CYLINDER COMBUSTION PRESSURE LEAKAGE
TEST
The combustion pressure leakage test provides an
accurate means for determining engine condition.
Combustion pressure leakage testing will detect:
• Exhaust and intake valve leaks (improper seating).
• Leaks between adjacent cylinders or into water
jacket.
• Any causes for combustion/compression pressure loss.
(1) Check the coolant level and fill as required. DO
NOT install the radiator cap.
(2) Start and operate the engine until it attains nor-
mal operating temperature, then turn the engine OFF.
(3) Remove the spark plugs.
(4) Remove the oil filler cap.
(5) Remove the air cleaner.
(6) Calibrate the tester according to the manufactur-
er’s instructions. The shop air source for testing should
maintain 483 kPa (70 psi) minimum, 1,379 kPa (200
psi) maximum and 552 kPa (80 psi) recommended.
(7) Perform the test procedures on each cylinder
according to the tester manufacturer’s instructions.
While testing, listen for pressurized air escaping
through the throttle body, tailpipe and oil filler cap
opening. Check for bubbles in the radiator coolant.
All gauge pressure indications should be equal,
with no more than 25% leakage.
FOR EXAMPLE: At 552 kPa (80 psi) input pres-
sure, a minimum of 414 kPa (60 psi) should be main-
tained in the cylinder.
Refer to the Cylinder Combustion Pressure Leak-
age Test Diagnosis chart.
XJ
2.5L ENGINE
9 - 13
DIAGNOSIS AND TESTING (Continued)
CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART
CONDITION
POSSIBLE CAUSE
CORRECTION
AIR ESCAPES THROUGH
THROTTLE BODY
Intake valve bent, burnt, or not
seated properly
Inspect valve and valve seat.
Reface or replace, as necessary
AIR ESCAPES THROUGH
TAILPIPE
Exhaust valve bent, burnt, or not
seated properly
Inspect valve and valve seat.
Reface or replace, as necessary
AIR ESCAPES THROUGH
RADIATOR
Head gasket leaking or cracked
cylinder head or block
Remove cylinder head and inspect.
Replace defective part
MORE THAN 50% LEAKAGE
FROM ADJACENT CYLINDERS
Head gasket leaking or crack in
cylinder head or block between
adjacent cylinders
Remove cylinder head and inspect.
Replace gasket, head, or block as
necessary
MORE THAN 25% LEAKAGE AND
AIR ESCAPES THROUGH OIL
FILLER CAP OPENING ONLY
Stuck or broken piston rings;
cracked piston; worn rings and/or
cylinder wall
Inspect for broken rings or piston.
Measure ring gap and cylinder
diameter, taper and out-of-round.
Replace defective part as necessary
ENGINE OIL LEAK INSPECTION
Begin with a thorough visual inspection of the
engine, particularly at the area of the suspected leak.
If an oil leak source is not readily identifiable, the
following steps should be followed:
(1) Do not clean or degrease the engine at this
time because some solvents may cause rubber to
swell, temporarily stopping the leak.
(2) Add an oil soluble dye (use as recommended by
manufacturer). Start the engine and let idle for
approximately 15 minutes. Check the oil dipstick to
make sure the dye is thoroughly mixed as indicated
with a bright yellow color under a black light.
(3) Using a black light, inspect the entire engine
for fluorescent dye, particularly at the suspected area
of oil leak. If the oil leak is found and identified,
repair per service manual instructions.
(4) If dye is not observed, drive the vehicle at var-
ious speeds for approximately 24km (15 miles), and
repeat inspection.
(4)
If the oil leak source is not positively
identified at this time, proceed with the air leak
detection test method.
Air Leak Detection Test Method
(1) Disconnect the breather cap to air cleaner hose
at the breather cap end. Cap or plug breather cap
nipple.
(2) Remove the PCV valve from the cylinder head
cover. Cap or plug the PCV valve grommet.
(3) Attach an air hose with pressure gauge and
regulator to the dipstick tube.
CAUTION: Do not subject the engine assembly to
more than 20.6 kpa (3 PSI) of test pressure.
(4) Gradually apply air pressure from 1 psi to 2.5
psi maximum while applying soapy water at the sus-
pected source. Adjust the regulator to the suitable
test pressure that provide the best bubbles which
will pinpoint the leak source. If the oil leak is
detected and identified, repair per service manual
procedures.
(5) If the leakage occurs at the rear oil seal area,
refer to the section, Inspection for Rear Seal Area
Leak.
(6) If no leaks are detected, turn off the air supply
and remove the air hose and all plugs and caps.
Install the PCV valve and breather cap hose.
(7) Clean the oil off the suspect oil leak area using
a suitable solvent. Drive the vehicle at various
speeds approximately 24 km (15 miles). Inspect the
engine for signs of an oil leak by using a black light.
INSPECTION FOR REAR SEAL AREA LEAKS
Since it is sometimes difficult to determine the
source of an oil leak in the rear seal area of the
engine, a more involved inspection is necessary. The
following steps should be followed to help pinpoint
the source of the leak.
If the leakage occurs at the crankshaft rear oil seal
area:
(1) Disconnect the battery.
(2) Raise the vehicle.
(3) Remove torque converter or clutch housing
cover and inspect rear of block for evidence of oil.
Use a black light to check for the oil leak:
(a) Circular spray pattern generally indicates
seal leakage or crankshaft damage.
(b) Where leakage tends to run straight down,
possible causes are a porous block, distributor seal,
camshaft bore cup plugs oil galley pipe plugs, oil
9 - 14
2.5L ENGINE
XJ
DIAGNOSIS AND TESTING (Continued)
filter runoff, and main bearing cap to cylinder
block mating surfaces.
(4) If no leaks are detected, pressurize the crank-
case as outlined in the, Inspection (Engine oil Leaks
in general)
CAUTION: Do not exceed 20.6 kPa (3 psi).
(5) If the leak is not detected, very slowly turn the
crankshaft and watch for leakage. If a leak is
detected between the crankshaft and seal while
slowly turning the crankshaft, it is possible the
crankshaft seal surface is damaged. The seal area on
the crankshaft could have minor nicks or scratches
that can be polished out with emery cloth.
CAUTION: Use extreme caution when crankshaft
polishing is necessary to remove minor nicks and
scratches. The crankshaft seal flange is especially
machined to complement the function of the rear oil
seal.
(6) For bubbles that remain steady with shaft
rotation, no further inspection can be done until dis-
assembled.
ENGINE OIL PRESSURE
(1) Disconnect connector and remove oil pressure
sending unit.
(2) Install Oil Pressure Line and Gauge Tool
C-3292 or equivalent. Start engine and record pres-
sure. Refer to Oil Pressure in Engine Specifications
for the correct pressures.
SERVICE PROCEDURES
VALVE TIMING
• Disconnect the spark plug wires and remove the
spark plugs.
• Remove the engine cylinder head cover.
• Remove the capscrews, bridge and pivot assem-
bly, and rocker arms from above the No.1 cylinder.
• Alternately loosen each capscrew, one turn at a
time, to avoid damaging the bridge.
• Rotate the crankshaft until the No.4 piston is at
top dead center (TDC) on the compression stroke.
• Rotate the crankshaft counterclockwise (viewed
from the front of the engine) 90°.
• Install a dial indicator on the end of the No.1
cylinder intake valve push rod. Use rubber tubing to
secure the indicator stem on the push rod.
• Set the dial indicator pointer at zero.
• Set the dial indicator pointer at zero.
• Rotate the crankshaft clockwise (viewed from
the front of the engine) until the dial indicator
pointer indicates 0.305 mm (0.012 inch) travel dis-
tance (lift).
• The timing notch index on the vibration damper
should be aligned with the TDC mark on the timing
degree scale.
• If the timing notch is more than 13 mm (1/2
inch) away from the TDC mark in either direction,
the valve timing is incorrect.
• If the valve timing is incorrect, the cause may be
a broken camshaft pin. It is not necessary to replace
the camshaft because of pin failure. A spring pin is
available for service replacement.
VALVE, GUIDE AND SEAL
Clean all carbon deposits from the combustion
chambers, valve ports, valve stems, valve stem
guides and head.
Clean all grime and gasket material from the
engine cylinder head machined gasket surface.
Inspect for cracks in the combustion chambers and
valve ports.
Inspect for cracks on the exhaust seat.
Inspect for cracks in the gasket surface at each
coolant passage.
Inspect valves for burned, cracked or warped
heads.
Inspect for scuffed or bent valve stems.
Replace valves displaying any damage.
VALVE REFACING
(1) Use a valve refacing machine to reface the
intake and exhaust valves to the specified angle.
(2) After refacing, a margin of at least 0.787 mm
(0.031 inch) must remain (Fig. 13). If the margin is
less than 0.787 mm (0.031 inch), the valve must be
replaced.
VALVE SEAT REFACING
(1) Install a pilot of the correct size in the valve
guide bore. Reface the valve seat to the specified
angle with a good dressing stone. Remove only
enough metal to provide a smooth finish.
(2) Use tapered stones to obtain the specified seat
width when required.
(3) Control valve seat runout to a maximum of
0.0635 mm (0.0025 in.)— (Fig. 14).
VALVE STEM OIL SEAL REPLACEMENT
Valve stem oil seals are installed on each valve
stem to prevent rocker arm lubricating oil from
entering the combustion chamber through the valve
guide bores. One seal is marked INT (intake valve)
and the other is marked EXH (exhaust valve).
Replace the oil seals whenever valve service is per-
formed or if the seals have deteriorated.
XJ
2.5L ENGINE
9 - 15
DIAGNOSIS AND TESTING (Continued)
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