2007 Commander XK Factory Service Manual 9 - ENGINE

DIAGNOSIS AND TESTING

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. Incorrect spark plug gap.
  		 4. (Refer to 8 - ELECTRICAL/IGNITION CONTROL/SPARK PLUG - CLEANING).
  		  
5. Dirt or water in fuel system.
  		 5. Clean system and replace fuel filter.
  		  
6. Faulty fuel pump, relay or wiring.
  		 6. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
 		  
ENGINE STALLS OR ROUGH IDLE
  		 1. Idle speed set to low.
  		 1. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
 
2. Vacuum leak.
  		 2. Inspect intake manifold and vacuum hoses, repair or replace as necessary.
  		  
3. Incorrect engine timing.
  		 3. (Refer to 9 - ENGINE/VALVE TIMING - STANDARD PROCEDURE).
  		  
ENGINE LOSS OF POWER
  		 1. Dirty or incorrectly gapped spark plugs.
  		 1. Replace spark plugs.
  
2. Dirt or water in fuel system.
  		 2. Clean system and replace fuel filter.
  		  
3. Blown cylinder head gasket.
  		 3. Replace cylinder head gasket.
  		  
4. Low compression.
  		 4. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
  		  
5. Burned, warped or pitted valves.
  		 5. Replace as necessary.
  		  
6. Plugged or restricted exhaust system.
  		 6. Inspect and replace as necessary.
  		  

DIAGNOSIS AND TESTING - 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
  		  

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

DIAGNOSIS AND TESTING - 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
  

DIAGNOSIS AND TESTING - ENGINE DIAGNOSIS - MECHANICAL

ENGINE MECHANICAL DIAGNOSIS CHART

CONDITION
  		 POSSIBLE CAUSES
  		 CORRECTION
  
NOISY VALVES/LIFTERS
  		 1. High or low oil level in crankcase
  		 1. Check for correct oil level. Adjust oil level by draining or adding as needed
  
2. Thin or diluted oil
  		 2. Change oil. (Refer to 9 - ENGINE/LUBRICATION/OIL - STANDARD PROCEDURE)
  		  
3. Low oil pressure
  		 3. Check engine oil level. If ok, Perform oil pressure test. (Refer to 9 - ENGINE/LUBRICATION - DIAGNOSIS AND TESTING) for engine oil pressure test/specifications
  		  
4. Dirt in tappets/lash adjusters
  		 4. Clean/replace hydraulic tappets/lash adjusters
  		  
5. Bent push rod(s)
  		 5. Install new push rods
  		  
6. Worn rocker arms
  		 6. Inspect oil supply to rocker arms and replace worn arms as needed
  		  
7. Worn tappets/lash adjusters
  		 7. Install new hydraulic tappets/lash adjusters
  		  
8. Worn valve guides
  		 8. Inspect all valve guides and replace as necessary
  		  
9. Excessive runout of valve seats or valve faces
  		 9. Grind valves and seats
  		  
CONNECTING ROD NOISE
  		 1. Insufficient oil supply
  		 1. Check engine oil level.
  
2. Low oil pressure
  		 2. Check engine oil level. If ok, Perform oil pressure test. (Refer to 9 - ENGINE/LUBRICATION - DIAGNOSIS AND TESTING) engine oil pressure test/specifications
  		  
3. Thin or diluted oil
  		 3. Change oil to correct viscosity. (Refer to 9 - ENGINE/LUBRICATION/OIL - STANDARD PROCEDURE) for correct procedure/engine oil specifications
  		  
4. Excessive connecting rod bearing clearance
  		 4. Measure bearings for correct clearance with plasti-gage. Repair as necessary
  		  
5. Connecting rod journal out of round
  		 5. Replace crankshaft or grind journals
  		  
6. Misaligned connecting rods
  		 6. Replace bent connecting rods
  		  
MAIN BEARING NOISE
  		 1. Insufficient oil supply
  		 1. Check engine oil level.
  
2. Low oil pressure
  		 2. Check engine oil level. If ok, Perform oil pressure test. (Refer to 9 - ENGINE/LUBRICATION - DIAGNOSIS AND TESTING)
  		  
3. Thin or diluted oil
  		 3. Change oil to correct viscosity.
  		  
4. Excessive main bearing clearance
  		 4. Measure bearings for correct clearance. Repair as necessary
  		  
5. Excessive end play
  		 5. Check crankshaft thrust bearing for excessive wear on flanges
  		  
6. Crankshaft main journal out of round or worn
  		 6. Grind journals or replace crankshaft
  		  
7. Loose flywheel or torque converter
  		 7. Inspect crankshaft, flexplate/flywheel and bolts for damage. Tighten to correct torque
  		  
LOW OIL PRESSURE
  		 1. Low oil level
  		 1. Check oil level and fill if necessary
  
2. Faulty oil pressure sending unit
  		 2. Install new sending unit
  		  
3. Clogged oil filter
  		 3. Install new oil filter
  		  
4. Worn oil pump
  		 4. Replace oil pump assembly.
  		  
5. Thin or diluted oil
  		 5. Change oil to correct viscosity.
  		  
6. Excessive bearing clearance
  		 6. Measure bearings for correct clearance
  		  
7. Oil pump relief valve stuck
  		 7. Remove valve to inspect, clean and reinstall
  		  
8. Oil pickup tube loose, broken, bent or clogged
  		 8. Inspect oil pickup tube and pump, and clean or replace if necessary
  		  
9. Oil pump cover warped or cracked
  		 9. Install new oil pump
  		  
OIL LEAKS
  		 1. Misaligned or deteriorated gaskets
  		 1. Replace gasket
  
2. Loose fastener, broken or porous metal part
  		 2. Tighten, repair or replace the part
  		  
3. Front or rear crankshaft oil seal leaking
  		 3. Replace seal
  		  
4. Leaking oil gallery plug or cup plug
  		 4. Remove and reseal threaded plug. Replace cup style plug
  		  
EXCESSIVE OIL CONSUMPTION OR SPARK PLUGS OIL FOULED
  		 1. CCV System malfunction
  		 1. (Refer to 25 - EMISSIONS CONTROL/EVAPORATIVE EMISSIONS - DESCRIPTION) for correct operation
  
2. Defective valve stem seal(s)
  		 2. Repair or replace seal(s)
  		  
3. Worn or broken piston rings
  		 3. Hone cylinder bores. Install new rings
  		  
4. Scuffed pistons/cylinder walls
  		 4. Hone cylinder bores and replace pistons as required
  		  
5. Carbon in oil control ring groove
  		 5. Remove rings and de-carbon piston
  		  
6. Worn valve guides
  		 6. Inspect/replace valve guides as necessary
  		  
7. Piston rings fitted too tightly in grooves
  		 7. Remove rings and check ring end gap and side clearance. Replace if necessary
  		  

DIAGNOSIS AND TESTING - ENGINE DIAGNOSIS - LUBRICATION
CONDITION
  		 POSSIBLE CAUSES
  		 CORRECTION
  
OIL LEAKS
  		 1. Gaskets and O-Rings.
  		 1. Replace as necessary.
  
(a) Misaligned or damaged.
  		 (a) Replace as necessary.
  		  
(b) Loose fasteners, broken or porous metal parts.
  		 (b) Tighten fasteners, Repair or replace metal parts.
  		  
2. Crankshaft rear seal
  		 2. Replace as necessary.
  		  
3. Crankshaft seal flange. Scratched, nicked or grooved.
  		 3. Polish or replace crankshaft.
  		  
4. Oil pan flange cracked.
  		 4. Replace oil pan.
  		  
5.Front cover seal, damaged or misaligned.
  		 5. Replace seal.
  		  
6. Scratched or damaged vibration damper hub.
  		 6. Polish or replace damper.
  		  
  7. Crankshaft Rear Flange Microporosity
  		 7. Replace Crankshaft
  
OIL PRESSURE DROP
  		 1. Low oil level.
  		 1. Check and correct oil level.
  
2. Faulty oil pressure sending unit.
  		 2. Replace sending unit.
  		  
3. Low oil pressure.
  		 3. Check pump and bearing clearance.
  		  
4. Clogged oil filter.
  		 4. Replace oil filter.
  		  
5. Worn oil pump.
  		 5. Replace as necessary.
  		  
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.
  		  
9. Oil pickup tube loose or damaged.
  		 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.
  		  
3. Incorrect ring size installed.
  		 3. Replace rings.
  		  
4. Worn valve guides.
  		 4. Ream guides and replace valves.
  		  
5. Leaking intake gasket.
  		 5. Replace intake gaskets.
  		  
6. Leaking valve guide seals.
  		 6. Replace valve guide seals.