by Russell Krick Publisher The Goodheart-Willcox Co., Inc Tinley Park, Illinois © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Locating engine performance problems Typical performance problems © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Engine performance problems, often called driveability problems, affect power, fuel economy, emission output levels, and dependability © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Strategy-Based Diagnostics Use a systematic approach Question the driver or service advisor about the symptoms and when they occur Look for the root cause of the failure © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only StrategyBased Diagnostics © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Diagnostic Example An injected engine misses and emits heavy black smoke after cold starting Heavy black smoke = too much fuel Only when cold = temperature related Engine coolant temperature sensor? ECM increases fuel when cold Temperature-related input (ECT sensor) may be the root cause © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Common Trouble Sources © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Troubleshooting Charts If you have trouble locating an engine performance problem, refer to a service manual troubleshooting chart Troubleshooting charts are based on symptoms Useful when no diagnostic trouble codes are present Suggests possible causes based on symptoms © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Troubleshooting Chart Fuel Supply System © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Misfiring One or more cylinders failing to fire normally at idle, under acceleration, or at cruise Causes of misfire at idle: fouled spark plugs or open plug wires a cracked distributor cap or corroded terminals vacuum leaks a problem with the carburetor’s idle circuit or its adjustment © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only OBD II Misfire Monitor Misfires can damage the catalytic converter When a cylinder misses, crankshaft acceleration will slow down slightly with the misfire The ECM monitors the crankshaft position sensor for this condition © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Scan Tool Misfire Data Misfire data values Misfire history Misfire passes Misfire failures Misfire rev status © Goodheart-Willcox Co., Inc Total misfires Misfiring cylinder RPM at misfire Load at misfire Permission granted to reproduce for educational use only Rough Idle Engine seems to vibrate Popping noise at the tailpipe caused by some of the cylinders not firing normally Causes: vacuum leaks lean air-fuel mixture spark plugs and wires © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Engine Performance Problems Engine performance over time © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Hesitation The engine does not accelerate normally Flat spot before developing power Often a temporarily lean condition Causes: faulty acceleration-related components faulty throttle position sensor faulty accelerator pump on carbureted systems © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Stumbling Engine misses, causing jerking on acceleration Causes: faulty oxygen sensor faulty throttle position sensor faulty engine coolant temperature sensor intermittent electrical problems causing loss of power to systems © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Surging Engine power fluctuates up and down with a continuous, soft jerking motion while driving at a steady speed Causes: extremely lean fuel injection or carburetor problems with the ignition or computer control systems problems with an electronically controlled automatic transmission intermittent electrical problems © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Backfiring Air-fuel mixture igniting in the intake manifold or exhaust system Loud bang or pop sound Causes: incorrect ignition timing, crossed spark plug wires, or a cracked distributor cap faulty ignition coil faulty throttle position sensor or computer faulty air injection system © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Dieseling or Run-On The engine fails to shut off, keeps firing after the ignition has been turned off Causes: high idle speed, overheated engine, low octane fuel, or cylinder carbon buildup © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Pinging (Spark Knock) Metallic tapping or light knocking sound on acceleration under load Abnormal combustion (preignition, detonation, or spark knock) Causes: low octane fuel advanced ignition timing carbon buildup overheating © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Vapor Lock Fuel is overheated, forming bubbles that upset mixture control Causes stalling, hard starting, or loss of power Causes: too much engine heat transferring into the fuel fuel line close to hot engine parts © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Fuel Line Freeze Moisture in the fuel turns to ice Blocks the filters and sharp bends in the fuel system Prevents engine operation Diesel fuel can form wax in cold weather © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Poor Fuel Economy Vehicle uses too much fuel for the distance driven Causes: rich air-fuel mixture engine miss incorrect ignition timing fuel leakage © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Lack of Power Sluggish engine, causes vehicle to accelerate slowly Causes: fuel system problems ignition system problems emission control problems engine mechanical problems © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only ... Locating engine performance problems Typical performance problems © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Engine performance problems, often called driveability. .. educational use only Engine Performance Problems Engine performance over time © Goodheart-Willcox Co., Inc Permission granted to reproduce for educational use only Hesitation The engine does not... fails to turn the crankshaft Starting system or engine mechanical problem starter, solenoid, and related wiring The starter spins but the engine does not turn starter drive or ring gear