Dodge RAM TRUCK 1500 1995 Service Manual page 849

BR ~ — _ ENGINES I - 5
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 per­
formance (engine idles rough and stalls) or mechani­
cal (a strange noise).
Refer to the Service Diagnosis—Performance chart
and the Service Diagnosis—Mechanical chart for pos­
sible causes and corrections of malfunctions. Refer to
Group 14, Fuel System for the fuel system diagnosis.
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 me­
chanical (a strange noise), or performance (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 diagno­
sis.
Additional tests and diagnostic procedures may be
necessary for specific engine malfunctions that can
not be isolated with the Service Diagnosis charts. In­
formation concerning additional tests and diagnosis
is provided within the following diagnosis:
• 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 E X T R E M E CAUTION W H E N THE
ENGINE IS OPERATING. DO WOT STAND IN A DI­
RECT LINE WITH THE FAN. DO MOT PUT YOUR
HANDS NEAR THE P U L L E Y S , B E L T S OR THE FAN.
DO NOT W E A R LOOSE CLOTHING.
(1) Start the engine.
(2) Spray a small stream of water at the suspected
leak area.
(3) If a change in RPM'S, 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) 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 3rd
revolution. Continue the test for the remaining cylin­
ders.
Refer to Engine Specifications for the correct en­
gine compression pressures.
ENGINE CYLINDER HEAD GASKET FAILURE
DIAGNOSIS
A leaking engine cylinder head gasket usually re­
sults in loss of power, loss of coolant and engine mis­
firing.
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.
CYLMfDER-TO-CYLINDER L E l I i i E 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.
CYUNDm-TO-WATER JACKET LEAKAGE
TEST
WARNING: U S E E X T R E M E CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND SN A DI­
RECT LINE WITH THE F A N . DO NOT PUT YOUR
HANDS NEAR THE P U L L E Y S , B E L T S OR THE FAN.
DO MOT W E A R 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 ex­
ists, bubbles will be visible in the coolant.
EUGIHE DIAGNOSIS