Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnosis And Testing: 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 performance (e.g., engine idles rough and stalls) or mechanical (e.g., a strange noise).
Refer to PERFORMANCE and MECHANICAL for possible causes and corrections of malfunctions.
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 diagnosis is provided within the following diagnosis:
- Cylinder Compression Pressure Test. Refer to CYLINDER COMPRESSION PRESSURE LEAKAGE .
- Cylinder Combustion Pressure Leakage Test. Refer to CYLINDER COMBUSTION PRESSURE LEAKAGE .
- Engine Cylinder Head Gasket Failure Diagnosis. Refer to DIAGNOSIS AND TESTING - CYLINDER HEAD GASKET FAILURE .
- Intake Manifold Leakage Diagnosis. Refer to MANIFOLD, INTAKE - DIAGNOSIS AND TESTING .
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.