Engine Performance Diagnostic Table

WARNING: This page is about a different car, the 2024 Jeep Grand Wagoneer L and 2024 Jeep Grand Wagoneer. However, it is still accessible from the selected car via links, so may be relevant.

CONDITION	POSSIBLE CAUSE	CORRECTION
ENGINE WILL NOT START	1. Weak battery.	1. Test the battery. Charge or replace as necessary. Refer to DIAGNOSIS AND TESTING - DUAL BATTERIES - 12 VOLT SYSTEM .
	2. Corroded or loose battery connections.	2. Clean and tighten the battery connections. Apply a coat of light mineral grease to the terminals. Refer to TORQUE SPECIFICATIONS .
	3. Faulty engine starting system.	3. Test the starting system. Refer to DIAGNOSIS AND TESTING .
	4. Faulty coil(s).	4. Test the ignition coil and replace as needed. Refer to DIAGNOSIS AND TESTING .
	5. Incorrect spark plug gap.	5. Check the spark plug gap. Refer to CAPACITIES AND RECOMMENDED FLUIDS, SPECIFICATIONS .
	6. Contamination in fuel system.	6. Clean the fuel system and replace the fuel filter. Refer to FILTER(S), FUEL, REMOVAL AND INSTALLATION .
	7. Faulty fuel pump.	7. Test the fuel pump and replace as needed. Refer to DIAGNOSIS AND TESTING .
	8. Incorrect cam timing.	8. Verify cam timing. Refer to VALVE TIMING VERIFICATION .
	9. Faulty Camshaft Position (CMP) sensor.	9. Replace the Camshaft Position (CMP) sensor. Refer to CAMSHAFT POSITION (CMP) SENSOR - EXHAUST or CAMSHAFT POSITION (CMP) SENSOR - INTAKE .
	10. Faulty Crankshaft Position (CKP) sensor.	10. Replace the Crankshaft Position (CKP) sensor. Refer to CRANKSHAFT POSITION (CKP) SENSOR .
ENGINE STALLS OR IDLES ROUGH	1. Idle speed too low.	1. Check for Diagnostic Trouble Codes (DTC). Refer to DIAGNOSTIC CODE INDEX .
	2. Incorrect fuel mixture.	2. Check for Diagnostic Trouble Codes (DTC). Refer to DIAGNOSTIC CODE INDEX .
	3. Vacuum leak.	3. Inspect intake manifold, manifold gasket, and vacuum hoses.
	4. Faulty ignition coil(s).	4. Test and replace the ignition coil. Refer to COIL, IGNITION, REMOVAL AND INSTALLATION .
	5. Faulty Crankshaft Position (CKP) sensor.	5. Replace the Crankshaft Position (CKP) sensor. Refer to CRANKSHAFT POSITION (CKP) SENSOR .
	6. Incorrect cam timing.	6. Verify cam timing. Refer to VALVE TIMING VERIFICATION .
ENGINE LOSS OF POWER	1. Dirty or incorrectly gapped spark plugs.	1. Correct as necessary. Refer to SPARK PLUG, REMOVAL AND INSTALLATION .
	2. Contamination in fuel system.	2. Clean the fuel system and replace the fuel filter if equipped.
	3. Faulty fuel pump.	3. Test and replace the fuel pump. Refer to ASSEMBLY, FUEL PUMP, REMOVAL AND INSTALLATION .
	4. Leaking cylinder head gasket.	4. Replace the cylinder head gasket. Refer to CYLINDER HEAD ASSEMBLY, REMOVAL AND INSTALLATION .
	5. Low compression.	5. Determine the cause and repair as necessary. Refer to ENGINE, DIAGNOSIS AND TESTING .
	6. Burned, warped, or pitted valves.	6. Replace valves as necessary. Refer to the appropriate Service Information .
	7. Plugged or restricted exhaust system.	7. Perform the exhaust restriction test. Install new parts as necessary. Refer to EXHAUST SYSTEM, DIAGNOSIS AND TESTING .
	8. Faulty ignition coil(s).	8. Test and replace the ignition coil. Refer to COIL, IGNITION, REMOVAL AND INSTALLATION .
	9. Incorrect valve timing.	9. Verify cam timing. Refer to VALVE TIMING VERIFICATION .
ENGINE MISSES ON ACCELERATION	1. Dirty or incorrectly gapped spark plugs.	1. Correct as necessary. Refer to SPARK PLUG, REMOVAL AND INSTALLATION .
	2. Contamination in fuel system.	2. Clean fuel system and replace the fuel filter if equipped.
	3. Burned, warped, or pitted valves.	3. Replace valves as necessary. Refer to the appropriate Service Information .
	4. Faulty ignition coil(s).	4. Test and replace the ignition coil. Refer to COIL, IGNITION, REMOVAL AND INSTALLATION .
ENGINE MISSES AT HIGH SPEED	1. Dirty or incorrect spark plug gap.	1. Correct as necessary. Refer to COIL, IGNITION, REMOVAL AND INSTALLATION .
	2. Faulty ignition coil(s).	2. Test and replace the ignition coil. Refer to COIL, IGNITION, REMOVAL AND INSTALLATION .
	3. Contamination in fuel system.	3. Clean the fuel system and replace the fuel filter if equipped.
	4. Dirty fuel injector(s).	4. Test and replace as necessary. Refer to DIAGNOSIS AND TESTING .