Page 19 of GM Goodwrench Engines Catalog by GM Goodwrench

GENERAL ENGINE DIAGNOSTICS Section IV Page 18 August 2004 DIAGNOSING AN ENGINE FAILURE Preliminary Checks Several preliminary checks are recommended when a customer arrives with a serious engine operating concern: 1. Understand the specific customer concern and the problem symptoms. 2. Verify the concern under the same conditions that it occurred. 3. Perform a visual/physical inspection for the following symptoms or signs of engine failure causes: Serious oil or coolant leaks which may indicate engine block cracks or cylinder head gasket failure. Engine noises that may indicate internal engine problems other than timing or fuel system defects. Overheating caused by inadequate cooling from a plugged radiator, stuck thermostat or collapsed coolant hoses. Excessive wear caused by a lack of lubrication from using an incorrect oil, inadequate oil changes, a too-low oil level, or a plugged filter, PCV valve or EGR valve. Incorrect timing causing overheating or performance problems. Unusual odors in the engine compartment, which may indicate excessive oil consumption, coolant hose/water pump failure, melted wiring or ruptured/melted seals or gaskets. Obvious exhaust emissions, with odor and colors, which may indicate combustion problems. Electrical failures from disconnected connectors or broken or melted wires. Engine performance problems from kinked, split or missing vacuum hoses. Hard starting, rough idling from collapsed or damaged air intake components. Electrical or mechanical malfunctions caused by improper installation of non-factory accessory items. 4. Never overlook the possibility that poor engine performance, even an inoperable condition, may be caused by problems in other systems starting/charging, ignition, fuel, intake and exhaust, lubrication, cooling, emission controls and engine controls. A weak battery, defective starter motor or failed generator will prevent proper engine start-up and may damage components. Incorrect ignition timing settings, as well as various defective ignition components, can easily shut down engine operations. Fuel system problems, such as blockage, contamination and defective/incorrect parts can cause serious engine concerns. Defective intake and exhaust systems can affect combustion quality and lead to detonation problems. Contaminated lubrication and cooling systems can lead to catastrophic engine failure. Insufficient engine cooling can lead to severe parts damage and even seizure from overheating. Emission-control settings and defective components may affect engine operation or cause serious problem symptoms. Electronic-control system components provide essential engine operating data to the PCM and must be checked with a scan tool or specific DTCs.

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