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