Dodge ram truck 3500 1996 Service Manual page 997

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ENGINE
9 - 7
ENGINE DIAGNOSIS
INDEX
page
DIAGNOSIS AND TESTING
CYLINDER COMBUSTION PRESSURE
LEAKAGE TEST 8
CYLINDER COMPRESSION PRESSURE TEST . . 7
ENGINE CYLINDER HEAD GASKET FAILURE
DIAGNOSIS . . 7
ENGINE DIAGNOSIS—GASOLINE-
MECHANICAL 12
ENGINE DIAGNOSIS—GASOLINE-
PERFORMANCE 11
ENGINE OIL PRESSURE 10
GENERAL INFORMATION . 7
D I A G N O S I S A N D T E S T I N G
GENERAL INFORMATION
Engine diagnosis is helpful in determining the
causes of malfunctions not detected and remedied by
routine tune-ups.
These malfunctions may be classified as either
mechanical (e.g., a strange noise), or performance
(e.g., engine idles rough and stalls).
Refer to the Service Diagnosis—Mechanical Chart
and the Service Diagnosis—Performance Chart, for
possible causes and corrections of malfunctions. Refer
to Group 14, Fuel System, for the fuel system diag­
nosis.
Additional tests and diagnostic procedures may be
necessary for specific engine malfunctions that can­
not be isolated with the Service Diagnosis charts.
Information concerning additional tests and diagno­
sis is provided within the following:
• Cylinder Compression Pressure Test
• Cylinder Combustion Pressure Leakage Test
• Engine Cylinder Head Gasket Failure Diagnosis
• Intake Manifold Leakage Diagnosis
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: U S E EXTREME CAUTION WHEN T H E
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR T H E P U L L E Y S , B E L T S , OR THE FAN.
DO NOT WEAR L O O S E CLOTHING.
(1) Start the engine.
page
HYDRAULIC TAPPETS 9
INSPECTION (ENGINE OIL LEAKS IN
GENERAL) 8
INSPECTION FOR REAR SEAL AREA LEAKS . . . 9
INTAKE MANIFOLD LEAKAGE DIAGNOSIS 7
SERVICE DIAGNOSIS—DIESEL-
MECHANICAL 21
SERVICE DIAGNOSIS—DIESEL-
PERFORMANCE 14
SERVICE DIAGNOSIS—GASOLINE-
LUBRICATION 13
(2) Spray a small stream of water at the suspected
leak area.
(3) I f a change in RPMs, the area of the suspected
leak has been found.
(4) Repair as required.
CYLINDER COMPRESSION P R E S S U R E 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) Disconnect the ignition coil.
(5) Insert a compression pressure gauge and rotate
the engine with the engine starter motor for three
revolutions.
(6) Record the compression pressure on the third
revolution. Continue the test for the remaining cylin­
ders.
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.