2007 Commander XK Factory Service Manual 9 - ENGINE

DIAGNOSIS AND TESTING

ENGINE DIAGNOSIS - 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 9 - ENGINE - DIAGNOSIS AND TESTING) - PERFORMANCE and (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)—MECHANICAL for possible causes and corrections of malfunctions. (Refer to 14 - FUEL SYSTEM/FUEL DELIVERY - DIAGNOSIS AND TESTING) and (Refer to 14 - FUEL SYSTEM/FUEL INJECTION - DIAGNOSIS AND TESTING) for the fuel system diagnosis.

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:

DIAGNOSIS AND TESTING - ENGINE DIAGNOSIS - PERFORMANCE


CONDITION
  		 POSSIBLE CAUSE
  		 CORRECTION
  
ENGINE WILL NOT START
  		 1. Weak battery
  		 1. Charge or replace as necessary.
  
2. Corroded or loose battery connections.
  		 2. Clean and tighten battery connections. Apply a coat of light mineral grease to the terminals.
  		  
3. Faulty starter.
  		 3. (Refer to 8 - ELECTRICAL/STARTING - DIAGNOSIS AND TESTING).
  		  
4. Faulty coil or control unit.
  		 4. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/IGNITION COIL - REMOVAL).
  		  
5. Incorrect spark plug gap.
  		 5. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/SPARK PLUG - CLEANING).
  		  
6. Dirt or water in fuel system.
  		 6. Clean system and replace fuel filter.
  		  
7. Faulty fuel pump, relay or wiring.
  		 7. Repair or replace as necessary.
  		  
ENGINE STALLS OR ROUGH IDLE
  		 1. Idle speed set to low.
  		 1. (Refer to 14 - FUEL SYSTEM/FUEL INJECTION/IDLE AIR CONTROL MOTOR - REMOVAL).
  
2. Idle mixture too lean or too rich.
  		 2. Refer to Powertrain Diagnosis Information.
  		  
3. Vacuum leak.
  		 3. Inspect intake manifold and vacuum hoses, repair or replace as necessary.
  		  
4. Faulty coil.
  		 4. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/IGNITION COIL - REMOVAL).
  		  
5. Incorrect engine timing.
  		 5. (Refer to 9 - ENGINE/VALVE TIMING - STANDARD PROCEDURE).
  		  
ENGINE LOSS OF POWER
  		 1. Dirty or incorrectly gapped spark plugs.
  		 1. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/SPARK PLUG - CLEANING).
  
2. Dirt or water in fuel system.
  		 2. Clean system and replace fuel filter.
  		  
3. Faulty fuel pump.
  		 3. Refer to the Appropriate Diagnostic Information
  		  
4. Blown cylinder head gasket.
  		 4. Replace cylinder head gasket.
  		  
5. Low compression.
  		 5. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
  		  
6. Burned, warped or pitted valves.
  		 6. Replace as necessary.
  		  
7. Plugged or restricted exhaust system.
  		 7. Inspect and replace as necessary.
  		  
8. Faulty coil.
  		 8. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/IGNITION COIL - REMOVAL).
  		  
ENGINE MISSES ON ACCELERATION
  		 1. Spark plugs dirty or incorrectly gapped.
  		 1. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/SPARK PLUG - CLEANING).
  
2. Dirt in fuel system.
  		 2. Clean fuel system.
  		  
3. Burned, warped or pitted valves.
  		 3. Replcae as necessary.
  		  
4. Faulty coil.
  		 4. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/IGNITION COIL - REMOVAL).
  		  
ENGINE MISSES AT HIGH SPEED
  		 1. Spark plugs dirty or incorrectly gapped.
  		 1. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/SPARK PLUG - CLEANING).
  
2. Faulty coil.
  		 2. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/IGNITION COIL - REMOVAL).
  		  
3. Dirt or water in fuel system.
  		 3. Clean system and replace fuel filter.
  		  

ENGINE DIAGNOSIS - MECHANICAL
CONDITION
  		 POSSIBLE CAUSES
  		 CORRECTIONS
  
NOISY VALVES
  		 1. High or low oil level in crankcase.
  		 1. (Refer to LUBRICATION & MAINTENANCE - SPECIFICATIONS)
 
2. Thin or diluted oil.
  		 2. Change oil and filter.
  		  
3. Low oil pressure.
  		 3. Check oil pump, if Ok, check rod and main bearings for excessive wear.
  		  
4. Dirt in lash adjusters.
  		 4. Replace as necessary.
  		  
5. Worn rocker arms.
  		 5. Replace as necessary.
  		  
6. Worn lash adjusters
  		 6. Replace as necessary.
  		  
7. Worn valve guides.
  		 7. (Refer to 9 - ENGINE/CYLINDER HEAD/INTAKE/EXHAUST VALVES & SEATS - STANDARD PROCEDURE)
 		  
8. Excessive runout of valve seats on valve faces.
  		 8. (Refer to 9 - ENGINE/CYLINDER HEAD/INTAKE/EXHAUST VALVES & SEATS - STANDARD PROCEDURE)
 		  
CONNECTING ROD NOISE
  		 1. Insufficient oil supply.
  		 1. (Refer to LUBRICATION & MAINTENANCE - SPECIFICATIONS)
 
2. Low oil pressure.
  		 2. Check oil pump, if Ok, check rod and main bearings for excessive wear.
  		  
3. Thin or diluted oil.
  		 3. Change oil and filter.
  		  
4. Excessive bearing clearance.
  		 4. Replace as necessary.
  		  
5. Connecting rod journal out-of-round.
  		 5. Service or replace crankshaft.
  		  
6. Misaligned connecting rods.
  		 6. Replace bent connecting rods.
  		  
MAIN BEARING NOISE
  		 1. Insufficient oil supply.
  		 1. (Refer to LUBRICATION & MAINTENANCE - SPECIFICATIONS)
 
2. Low oil pressure.
  		 2. Check oil pump, if Ok, check rod and main bearings for excessive wear.
  		  
3. Thin or diluted oil.
  		 3. Change oil and filter.
  		  
4. Excessive bearing clearance.
  		 4. Replace as necessary.
  		  
5. Excessive end play.
  		 5. Check thrust washers for wear.
  		  
6. Crankshaft journal out-of round.
  		 6. Service or replace crankshaft.
  		  
7. Loose flywheel or torque converter.
  		 7. Tighten to correct torque
  		  

ENGINE DIAGNOSIS - LUBRICATION
CONDITION
  		 POSSIBLE CAUSES
  		 CORRECTION
  
OIL LEAKS
  		 1. Gaskets and O-Rings. Misaligned or damaged.
  		 1. Replace as necessary.
  
(a) Loose fasteners, broken or porous metal parts.
  		 (a) Tighten fasteners, Repair or replace metal parts.
  		  
2. Crankshaft rear seal
  		 2. Replace as necessary (Refer to 9 - ENGINE/ENGINE BLOCK/CRANKSHAFT OIL SEAL - REAR - REMOVAL).
  		  
3. Crankshaft seal flange. Scratched, nicked or grooved.
  		 3. Polish or replace crankshaft.
  		  
4. Oil pan flange cracked.
  		 4. Replace oil pan (Refer to 9 - ENGINE/LUBRICATION/OIL PAN - REMOVAL).
  		  
5. Timing chain cover seal, damaged or misaligned.
  		 5. Replace seal (Refer to 9 - ENGINE/ENGINE BLOCK/CRANKSHAFT OIL SEAL - FRONT - REMOVAL).
  		  
6. Scratched or damaged vibration damper hub.
  		 6. Polish or replace damper.
  		  
OIL PRESSURE DROP
  		 1. Low oil level.
  		 1. Check and correct oil level.
  
2. Faulty oil pressure sending unit.
  		 2. Replace sending unit (Refer to 9 - ENGINE/LUBRICATION/OIL PRESSURE SENSOR/SWITCH - REMOVAL).
  		  
3. Low oil pressure.
  		 3. Check oil pump and bearing clearance.
  		  
4. Clogged oil filter.
  		 4. Replace oil filter (Refer to 9 - ENGINE/LUBRICATION/OIL FILTER - REMOVAL).
  		  
5. Worn oil pump.
  		 5. Replace oil pump (Refer to 9 - ENGINE/LUBRICATION/OIL PUMP - REMOVAL).
  		  
6. Thin or diluted oil.
  		 6. Change oil and filter.
  		  
7. Excessive bearing clearance.
  		 7. Replace as necessary.
  		  
8. Oil pump relief valve stuck.
  		 8. Replace oil pump (Refer to 9 - ENGINE/LUBRICATION/OIL PUMP - REMOVAL).
  		  
9. Oil pick up tube loose, damaged or clogged.
  		 9. Replace as necessary.
  		  
OIL PUMPING AT RINGS; SPARK PLUGS FOULING
  		 1. Worn or damaged rings.
  		 1. Hone cylinder bores and replace rings.
  
2. Carbon in oil ring slots.
  		 2. Replace rings (Refer to 9 - ENGINE/ENGINE BLOCK/PISTON RINGS - STANDARD PROCEDURE).
  		  
3. Incorrect ring size installed.
  		 3. Replace rings (Refer to 9 - ENGINE/ENGINE BLOCK/PISTON RINGS - STANDARD PROCEDURE).
  		  
4. Worn valve guides.
  		 4. Ream guides and replace valves (Refer to 9 - ENGINE/CYLINDER HEAD/INTAKE/EXHAUST VALVES & SEATS - STANDARD PROCEDURE).
  		  
5. Leaking valve guide seals.
  		 5. Replace valve guide seals.
  		  

DIAGNOSIS AND TESTING - CYLINDER COMPRESSION PRESSURE

The results of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions.

Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise the indicated compression pressures may not be valid for diagnosis purposes.


1. Clean the spark plug recesses with compressed air.
2. Remove the spark plugs.
3. Secure the throttle in the wide-open position.
4. Disable the fuel system (Refer to 14 - FUEL SYSTEM/FUEL DELIVERY - DESCRIPTION).
5. Remove the ASD relay (Refer to 8 - ELECTRICAL/IGNITION CONTROL/AUTO SHUT DOWN RELAY - REMOVAL).
6. Insert a compression pressure gauge and rotate the engine with the engine starter motor for three revolutions.
7. Record the compression pressure on the 3rd revolution. Continue the test for the remaining cylinders.
8. (Refer to 9 - ENGINE - SPECIFICATIONS) for the correct engine compression pressures.

CYLINDER COMBUSTION PRESSURE LEAKAGE

The combustion pressure leakage test provides an accurate means for determining engine condition.

Combustion pressure leakage testing will detect:


1. Check the coolant level and fill as required. DO NOT install the radiator cap.
2. Start and operate the engine until it attains normal operating temperature, then turn the engine OFF.
3. Remove the spark plugs.
4. Remove the oil filler cap.
5. Remove the air cleaner hose.
6. Calibrate the tester according to the manufacturer's instructions. The shop air source for testing should maintain 483 kPa (70 psi) minimum, 1,379 kPa (200 psi) maximum and 552 kPa (80 psi) recommended.
7. Perform the test procedures on each cylinder according to the tester manufacturer's instructions. Set piston of cylinder to be tested at TDC compression,While testing, listen for pressurized air escaping through the throttle body, tailpipe and oil filler cap opening. Check for bubbles in the radiator coolant.

All gauge pressure indications should be equal, with no more than 25% leakage.

FOR EXAMPLE: At 552 kPa (80 psi) input pressure, a minimum of 414 kPa (60 psi) should be maintained in the cylinder.

Refer to CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART.


CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART

CONDITION
  		POSSIBLE CAUSE
  		CORRECTION
  
AIR ESCAPES THROUGH THROTTLE BODY
  		Intake valve bent, burnt, or not seated properly
  		Inspect valve and valve seat. Reface or replace, as necessary. Inspect valve springs. Replace as necessary.
  
AIR ESCAPES THROUGH TAILPIPE
  		Exhaust valve bent, burnt, or not seated properly
  		Inspect valve and valve seat. Reface or replace, as necessary. Inspect valve springs. Replace as necessary.
  
AIR ESCAPES THROUGH RADIATOR
  		Head gasket leaking or cracked cylinder head or block
  		Remove cylinder head and inspect. Replace defective part
  
MORE THAN 50% LEAKAGE FROM ADJACENT CYLINDERS
  		Head gasket leaking or crack in cylinder head or block between adjacent cylinders
  		Remove cylinder head and inspect. Replace gasket, head, or block as necessary
  
MORE THAN 25% LEAKAGE AND AIR ESCAPES THROUGH OIL FILLER CAP OPENING ONLY
  		Stuck or broken piston rings; cracked piston; worn rings and/or cylinder wall
  		Inspect for broken rings or piston. Measure ring gap and cylinder diameter, taper and out-of-round. Replace defective part as necessary