DIAGNOSIS AND TESTING
ENGINE DIAGNOSIS—INTRODUCTION
Engine diagnosis is helpful in determining the
causes of malfunctions not detected and remedied by
routine maintenance.
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 FUEL SYSTEM for the fuel system diagnosis.
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
• Cylinder Head Gasket Failure Diagnosis
• Intake Manifold Leakage Diagnosis
• Lash Adjuster (Tappet) Noise Diagnosis
• Engine Oil Leak Inspection
ENGINE DIAGNOSIS—PERFORMANCE
CONDITION POSSIBLE CAUSE CORRECTION
ENGINE WILL NOT START 1. Weak battery. 1. Test battery. Charge or replace as
necessary. Refer to BATTERY.
2. Corroded or loose battery
connections.
2. Clean and tighten battery
connections. Apply a coat of light
mineral grease to terminals.
3. Faulty starter. 3. Test starting system. Refer to
STARTING.
4. Faulty coil(s) or control unit. 4. Test and replace as needed. Refer to
IGNITION SYSTEM.
5. Incorrect spark plug gap. 5. Set gap. Refer to IGNITION
SYSTEM.
6. Contamination in fuel system. 6. Clean system and replace fuel filter.
7. Faulty fuel pump. 7. Test fuel pump and replace as
needed. Refer to FUEL SYSTEM.
8. Incorrect engine timing. 8. Check for a skipped timing belt/chain
or a loose camshaft sprocket (3.2/3.5L).
ENGINE STALLS OR
IDLES ROUGH
1. Idle speed too low. 1. Test minimum air flow. Refer to FUEL
SYSTEM.
2. Incorrect fuel mixture. 2. Refer to FUEL SYSTEM.
3. Intake manifold leakage. 3. Inspect intake manifold, manifold
gasket, and vacuum hoses.
4. Faulty coil(s). 4. Test and replace as necessary. Refer
to IGNITION SYSTEM.
LH 2.7L ENGINE 9 - 13
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