Cylinder Combustion Pressure Leakage Test; Cylinder Head Gasket Failure Diagnosis; Cyllnder-To-Cylinder Leakage Test - Jeep J-10 Series 1982 Technical & Service Manual

1A-14 GENERAL SERVICE AND DIAGNOSIS
CYLINDER COMBUSTION PRESSURE LEAKAGE TEST
Satisfactory engine performance depends upon a me
chanically sound engine. In many instances, unsatisfac
tory performance or rough idle is caused by combustion
chamber leakage. A cylinder compression pressure test
alone may not reveal this fault. The pressure leakage
test outlined below provides an accurate means of eval
uating engine condition. Pressure leakage testing will
indicate if the exhaust or intake valves are improperly
seated, if leaks exist between adjacent cylinders, if there
are leaks into the water jacket and any other causes of
compression pressure loss.
(1) Inspect coolant level and add as required. Do not
install radiator cap.
(2) Start and operate engine until it attains normal
operating temperature, then turn ignition Off.
(3) Remove spark plugs.
(4) Remove oil filler cap.
(5) Remove air cleaner.
(6) Position carburetor fast idle speed screw on top
step of fast idle cam.
(7) Calibrate test equipment according to manufac
turer's instructions.
NOTE: Shop air source for testing should maintain 70
psi (483 kPa) minimum and 200 psi (1380 kPa) maximum
(80 psi [552 kPa] recommended).
(8) Perform test procedure on each cylinder accord
ing to equipment manufacturer's instructions.
NOTE: While testing, listen for air escaping through
carburetor, tailpipe and oil filler opening, and look for
bubbles in radiator coolant.
(9) All gauge indications should be equal, with no
more than 25 percent leakage. For example, at 80 psi
(552 kPa) input pressure, a minimum of 60 psi (414 kPa)
should be maintained in cylinder. Refer to Cylinder
Combustion Pressure Leakage Test Diagnosis.
CYLINDER HEAD GASKET FAILURE DIAGNOSIS
A "blown" cylinder head gasket usually results in a
loss of power, loss of coolant and engine misfire. A
"blown" cylinder head gasket may develop between ad
jacent cylinders or between a cylinder and adjacent wa
ter jacket.
A cylinder head gasket "blown" between two adjacent
cylinders is usually indicated by a loss of power and
engine misfire.
A cylinder head gasket "blown" between a cylinder
and an adjacent water jacket is indicated by foaming of
coolant or overheating and loss of coolant.
Replace a "blown" cylinder head gasket using the pro
cedure outlined in Chapter IB—Engines.
Cyllnder-to-CyUBdsr Leakage Test
To determine if the cylinder head gasket is "blown"
between cylinders, perform a compression pressure test
as outlined under Cylinder Compression Pressure Test.
A cylinder head gasket "blown" between two cylinders
will result in approximately a 50 to 70 percent reduction
in compression pressure in the two affected cylinders.
Cylinder Combustion Pressure Leakage Test Diagnosis
Condition Possible Cause
Correction
(1) Air escapes
through
carburetor.
(1)
Intake valve leaks.
(1)
Refer to Valve Reconditioning
(Chapter IB).
(2) Air escapes
through tailpipe.
(2)
Exhaust valve leaks. (2)
Refer to Valve Reconditioning
(Chapter IB).
(S) Air escapes
through radiator.
(3) Head gasket leaks or crack
in cylinder block.
(3)
Remove cylinder head
and inspect.
(4) More than 25%
leakage into
adjacent cylinder.
(4)
Head gasket leaks or crack
in cylinder block or head
between adjacent cylinders.
(4)
Remove cylinder head
and inspect.
(5) More than 25%
leakage and
air escapes
through oil
filler cap open
ing only.
(5)
Stuck or broken piston ring(s);
cracked piston; worn rings
and/or cylinder wall.
(5)
Inspect for broken ring(s) or
piston. Measure ring gap and
cylinder diameter, taper, and
out-of-round.
7033S