2007 Wrangler JK 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 mechanical (e.g., a strange noise), or performance (e.g., engine idles rough and stalls).

Refer to the Engine Mechanical and the Engine Performance diagnostic charts, for possible causes and corrections of malfunctions (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING) (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING - PERFORMANCE).

For fuel system diagnosis, (Refer to 14 - FUEL SYSTEM/FUEL DELIVERY - DIAGNOSIS AND TESTING).

Additional tests and diagnostic procedures may be necessary for specific engine malfunctions that cannot be isolated with the Service Diagnosis charts. Information concerning additional tests and diagnosis is provided within the following:

DIAGNOSIS AND TESTING - ENGINE DIAGNOSIS - PERFORMANCE


CONDITION
  		 POSSIBLE CAUSE
  		 CORRECTION
  
ENGINE WILL NOT START
  		 1. Weak battery.
  		 1. Test battery. Charge or replace as necessary
(Refer to 8 - ELECTRICAL/BATTERY SYSTEM - DIAGNOSIS AND TESTING)
 
2. Corroded or loose battery connections.
  		 2. Clean and tighten battery connections. Apply a coat of light mineral grease to terminals.
  		  
3. Faulty starter.
  		 3. Test starting system. (Refer to 8 - ELECTRICAL/STARTING - DIAGNOSIS AND TESTING)
 		  
4. Faulty coil(s) or control unit.
  		 4. Test and replace as needed. (Refer to Appropriate Diagnostic Information)
  		  
5. Incorrect spark plug gap.
  		 5. Set gap. (Refer to 8 - ELECTRICAL/IGNITION CONTROL - SPECIFICATIONS)
 		  
6. Contamination in fuel system.
 		 6. Clean system and replace fuel filter.
  		  
7. Faulty fuel pump.
  		 7. Test fuel pump and replace as needed. (Refer to Appropriate Diagnostic Information)
  		  
  8. Incorrect engine timing.
  		 8. Check for a skipped timing belt/chain.
  
ENGINE STALLS OR IDLES ROUGH
  		 1. Idle speed too low.
  		 1. Test minimum air flow. (Refer to Appropriate Diagnostic Information)
  
2. Incorrect fuel mixture.
  		 2. (Refer to Appropriate Diagnostic Information)
  		  
3. Intake manifold leakage.
  		 3. Inspect intake manifold, manifold gasket, and vacuum hoses.
  		  
4. Faulty ignition coil(s).
  		 4. Test and replace as necessary. (Refer to Appropriate Diagnostic Information)
  		  
ENGINE LOSS OF POWER
  		 1. Dirty or incorrectly gapped plugs.
  		 1. Clean plugs and set gap.
 
2. Contamination in fuel system.
  		 2. Clean system and replace fuel filter.
  		  
3. Faulty fuel pump.
  		 3. Test and replace as necessary. (Refer to Appropriate Diagnostic Information)
  		  
4. Incorrect valve timing.
  		 4. Correct valve timing.
  		  
5. Leaking cylinder head gasket.
  		 5. Replace cylinder head gasket.
  		  
6. Low compression.
  		 6. Test compression of each cylinder.
  		  
7. Burned, warped, or pitted valves.
  		 7. Replace valves.
  		  
8. Plugged or restricted exhaust system.
  		 8. Perform exhaust restriction test. (Refer to 11 - EXHAUST SYSTEM - DIAGNOSIS AND TESTING) Install new parts, as necessary.
  		  
9. Faulty ignition coil(s).
  		 9. Test and replace as necessary. (Refer to Appropriate Diagnostic Information)
  		  
ENGINE MISSES ON ACCELERATION
  		 1. Dirty or incorrectly gapped spark plugs.
  		 1. Clean spark plugs and set gap.
 
2. Contamination in Fuel System.
  		 2. Clean fuel system and replace fuel filter.
  		  
3. Burned, warped, or pitted valves.
  		 3. Replace valves.
  		  
4. Faulty ignition coil(s).
  		 4. Test and replace as necessary. (Refer to Appropriate Diagnostic Information)
  		  
ENGINE MISSES AT HIGH SPEED
  		 1. Dirty or incorrect spark plug gap.
  		 1. Clean spark plugs and set gap.
  
2. Faulty ignition coil(s).
  		 2. Test and replace as necessary. (Refer to Appropriate Diagnostic Information)
  		  
3. Dirty fuel injector(s).
  		 3. Test and replace as necessary. (Refer to Appropriate Diagnostic Information)
  		  
4. Contamination in fuel system.
  		 4. Clean system and replace fuel filter.
  		  

ENGINE DIAGNOSIS - MECHANICAL
CONDITION
  		 POSSIBLE CAUSES
  		 CORRECTION
  
NOISY VALVES
  		 1. High or low oil level in crankcase.
  		 1. Check and correct engine oil level.
  
2. Thin or diluted oil.
  		 2. Change oil to correct viscosity.
  		  
3. Thick oil
  		 3. (a) Change engine oil and filter.
  		  
  (b) Run engine to operating temperature.
  
  (c) Change engine oil and filter again.
  
4. Low oil pressure.
  		 4. Check and correct engine oil pressure problem.
  		  
5. Dirt in hydraulic lifters/lash adjusters.
  		 5. Replace hydraulic lifters/lash adjusters.
  		  
6. Worn rocker arms.
  		 6. Inspect oil supply to rocker arms.
  		  
7. Worn hydraulic lifters/lash adjusters.
  		 7. Replace hydraulic lifters/lash adjusters.
  		  
8. Worn valve guides.
  		 8. Replace cylinder head assembly.
  		  
9. Excessive runout of valve seats on valve faces.
  		 9. Grind valve seats and valves.
  		  
CONNECTING ROD NOISE
  		 1. Insufficient oil supply.
  		 1. Check engine oil level.
 
2. Low oil pressure.
  		 2. Check engine oil level. Inspect oil pump relief valve and spring.
  		  
3. Thin or diluted oil.
  		 3. Change oil to correct viscosity.
  		  
4. Thick oil
  		 4. (a) Change engine oil and filter.
  		  
  (b) Run engine to operating temperature.
  
  (c) Change engine oil and filter again.
  
5. Excessive bearing clearance.
  		 5. Measure bearings for correct clearance. Repair as necessary.
  		  
6. Connecting rod journal out-of-round.
  		 6. Replace crankshaft or grind surface.
  		  
7. Misaligned connecting rods.
 		 7. 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. Inspect oil pump relief valve and spring.
  		  
3. Thin or diluted oil.
  		 3. Change oil to correct viscosity.
  		  
4. Thick oil
  		 4. (a) Change engine oil and filter.
  		  
  (b) Run engine to operating temperature.
  
  (c) Change engine oil and filter again.
  
5. Excessive bearing clearance.
  		 5. Measure bearings for correct clearance. Repair as necessary.
  		  
6. Excessive end play.
  		 6. Check thrust bearing for wear on flanges.
  		  
7. Crankshaft journal out-of-round or worn.
  		 7. Replace crankshaft or grind journals.
  		  
8. Loose flywheel or torque converter.
  		 8. Tighten to correct torque.
  		  
OIL PRESSURE DROP
  		 1. Low oil level.
  		 1. Check engine oil level.
  
2. Faulty oil pressure sensor/switch.
  		 2. Replace oil pressure sensor/switch.
  		  
3. Low oil pressure.
  		 3. Check oil pressure sensor/switch and main bearing oil clearance.
  		  
4. Clogged oil filter.
  		 4. Install new oil filter.
  		  
5. Worn parts in oil pump.
  		 5. Replace worn parts or pump.
  		  
6. Thin or diluted oil.
  		 6. Change oil to correct viscosity.
  		  
7. Oil pump relief valve stuck.
  		 7. Remove valve and inspect, clean, or replace.
  		  
8. Oil pump suction tube loose.
  		 8. Remove oil pan and install new tube or clean, if necessary.
  		  
9. Oil pump cover warped or cracked.
 		 9. Install new oil pump.
  		  
10. Excessive bearing clearance.
  		 10. Measure bearings for correct clearance.
  		  
OIL LEAKS
  		 1. Misaligned or deteriorated gaskets.
  		 1. Replace gasket(s).
  
2. Loose fastener, broken or porous metal part.
  		 2. Tighten, repair or replace the part.
  		  
3. Misaligned or deteriorated cup or threaded plug.
  		 3. Replace as necessary.
  		  
OIL CONSUMPTION OR SPARK PLUGS FOULED
  		 1. PCV system malfunction.
  		 1. Check system and repair as necessary. (Refer to 25 - EMISSIONS CONTROL/EVAPORATIVE EMISSIONS/PCV VALVE - DIAGNOSIS AND TESTING)
 
2. Worn, scuffed or broken rings.
  		 2. Hone cylinder bores. Install new rings.
  		  
3. Carbon in oil ring slots.
  		 3. Install new rings.
  		  
4. Rings fitted too tightly in grooves.
  		 4. Remove rings and check grooves. If groove is not proper width, replace piston.
  		  
5. Worn valve guide(s).
  		 5. Replace cylinder head assembly.
  		  
6. Valve stem seal(s) worn or damaged.
  		 6. Replace seal(s).
  		  

ENGINE OIL LEAK INSPECTION

Begin with a thorough visual inspection of the engine, particularly at the area of the suspected leak. If an oil leak source is not readily identifiable, the following steps should be followed:


1. Do not clean or degrease the engine at this time because some solvents may cause rubber to swell, temporarily stopping the leak.
2. Add an oil soluble dye (use as recommended by manufacturer). Start the engine and let idle for approximately 15 minutes. Check the oil oil level indicator to make sure the dye is thoroughly mixed as indicated with a bright yellow color under a black light.
3. Using a black light, inspect the entire engine for fluorescent dye, particularly at the suspected area of oil leak. If the oil leak is found and identified, repair as necessary.
4. If dye is not observed, drive the vehicle at various speeds for approximately 24 km (15 miles), and repeat inspection.
5. If the oil leak source is not positively identified at this time, proceed with the air leak detection test method as follows:
  • Disconnect the fresh air hose (make-up air) at the cylinder head cover and plug or cap the outlet on the cover.
  • Remove the PCV valve hose from the cylinder head cover. Cap or plug the PCV valve outlet on the cover.
  • Attach an air hose with pressure gauge and regulator to the oil level indicator tube.

    CAUTION: Do not subject the engine assembly to more than 20.6 kpa (3 PSI) of test pressure.

  • Gradually apply air pressure from 1 psi to 2.5 psi maximum while applying soapy water at the suspected source. Adjust the regulator to the suitable test pressure that provides the best bubbles which will pinpoint the leak source. If the oil leak is detected and identified, repair per service manual procedures.
  • If the leakage occurs at the crankshaft rear oil seal area, refer to the section, Inspection for Rear Seal Area Leak.

6. If no leaks are detected, turn off the air supply. Remove the air hose, all plugs, and caps. Install the PCV valve and fresh air hose (make-up air). Proceed to next step.
7. Clean the oil off the suspect oil leak area using a suitable solvent. Drive the vehicle at various speeds approximately 24 km (15 miles). Inspect the engine for signs of an oil leak by using a black light.

NOTE: If oil leakage is observed at the oil level indicator tube to block location; remove the tube, clean and reseal using Mopar® Stud & Bearing Mount (press fit tube applications only), and for O-ring style tubes, remove tube and replace the O-ring seal.


INSPECTION FOR REAR SEAL AREA LEAKS

Since it is sometimes difficult to determine the source of an oil leak in the rear seal area of the engine, a more involved inspection is necessary. The following steps should be followed to help pinpoint the source of the leak.

If the leakage occurs at the crankshaft rear oil seal area:


1. Disconnect the battery.
2. Raise the vehicle.
3. Remove torque converter or clutch housing cover and inspect rear of block for evidence of oil. Use a black light to check for the oil leak. If a leak is present in this area, remove transmission for further inspection.
a. Circular spray pattern generally indicates seal leakage or crankshaft damage.
b. Where leakage tends to run straight down, possible causes are a porous block, oil gallery cup plug, bedplate to cylinder block mating surfaces and seal bore. See proper repair procedures for these items.
4. If no leaks are detected, pressurize the crankcase as previously described.

CAUTION: Do not exceed 20.6 kPa (3 psi).


5. If the leak is not detected, very slowly turn the crankshaft and watch for leakage. If a leak is detected between the crankshaft and seal while slowly turning the crankshaft, it is possible the crankshaft seal surface is damaged. The seal area on the crankshaft could have minor nicks or scratches that can be polished out with emery cloth.

CAUTION: Use extreme caution when crankshaft polishing is necessary to remove minor nicks and scratches. The crankshaft seal flange is especially machined to complement the function of the rear oil seal.


6. For bubbles that remain steady with shaft rotation, no further inspection can be done until disassembled.
7. After the oil leak root cause and appropriate corrective action have been identified, replace component(s) as necessary.

DIAGNOSIS AND TESTING - CYLINDER COMPRESSION PRESSURE TEST

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. Check engine oil level and add oil if necessary.
2. Drive the vehicle until engine reaches normal operating temperature. Select a route free from traffic and other forms of congestion, observe all traffic laws, and accelerate through the gears several times briskly.
3. Remove all spark plugs from engine. As spark plugs are being removed, check electrodes for abnormal firing indicators fouled, hot, oily, etc. Record cylinder number of spark plug for future reference.
4. Remove the Auto Shutdown (ASD) relay from the PDC.
5. Be sure throttle blade is fully open during the compression check.
6. Insert compression gauge adaptor Special Tool 8116 or the equivalent, into the #1 spark plug hole in cylinder head. Connect the 0–500 psi (Blue) pressure transducer (Special Tool CH7059) with cable adaptors to the DRBIII®. For Special Tool identification, (Refer to 9 - ENGINE - SPECIAL TOOLS).
7. Crank engine until maximum pressure is reached on gauge. Record this pressure as #1 cylinder pressure.
8. Repeat the previous step for all remaining cylinders.
9. Compression should not be less than 689 kPa (100 psi) and not vary more than 25 percent from cylinder to cylinder.
10. If one or more cylinders have abnormally low compression pressures, repeat the compression test.
11. If the same cylinder or cylinders repeat an abnormally low reading on the second compression test, it could indicate the existence of a problem in the cylinder in question. The recommended compression pressures are to be used only as a guide to diagnosing engine problems. An engine should not be disassembled to determine the cause of low compression unless some malfunction is present.

CYLINDER COMBUSTION PRESSURE LEAKAGE TEST

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

Combustion pressure leakage testing will detect:

WARNING: DO NOT REMOVE THE PRESSURE CAP WITH THE SYSTEM HOT AND UNDER PRESSURE BECAUSE SERIOUS BURNS FROM COOLANT CAN OCCUR.

Check the coolant level and fill as required. DO NOT install the pressure cap.

Start and operate the engine until it attains normal operating temperature, then turn the engine OFF.

Clean spark plug recesses with compressed air.

Remove the spark plugs.

Remove the oil filler cap.

Remove the air cleaner.

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, with 552 kPa (80 psi) recommended.

Perform the test procedures on each cylinder according to the tester manufacturer's instructions. While testing, listen for pressurized air escaping through the throttle body, tailpipe and oil filler cap opening. Check for bubbles in the coolant.

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

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