Dodge Nitro. Manual - part 67

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. Thick/Thin or diluted oil.

3. Change oil to correct viscosity.

-

3. (a.) Change oil and filter.

(b.) Run engine to operating 
temperature.
(c.) Change oil and filter again.
4. Excessive bearing clearance.

4. Measure bearings for correct 
clearance. Repair as necessary.

5. Connecting rod journal out-of-
round.

5. Replace crankshaft or grind 
surface.

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. Inspect 
oil pump relief valve and spring.

3. Thick/Thin or diluted oil.

3. Change oil to correct viscosity.

-

3. (a.) Change oil and filter.

(b.) Run engine to operating 
temperature.
(c.) Change oil and filter again.
4. Excessive bearing clearance.

4. Measure bearings for correct 
clearance. Repair as necessary.

5. Excessive end play.

5. Check thrust bearing for wear 
on flanges.

6. Crankshaft journal out-of-round 
or worn.

6. Replace crankshaft or grind 
journals.

7. Loose flywheel or torque 
converter.

7. Tighten to correct torque.

OIL PRESSURE DROP

1. Low oil level.

1. Check engine oil level.

2. Faulty oil pressure sending unit. 2. Install new sending unit.
3. Low oil pressure.

3. Check sending unit 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.

 

2007 Dodge Nitro R/T 

2007 ENGINE 4.0L - Service Information - Nitro

  

CYLINDER COMBUSTION PRESSURE LEAKAGE TEST 

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

Combustion pressure leakage testing will detect: 

Exhaust and intake valve leaks (improper seating).  

Leaks between adjacent cylinders or into water jacket.  

Any causes for combustion/compression pressure loss.  

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

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

3. Clean spark plug recesses with compressed air.  

4. Remove the spark plugs.  

5. Remove the oil filler cap.  

6. Remove the air cleaner.  

7. 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. 

8. Perform the test procedures on each cylinder according to the tester manufacturer's instructions. While 

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 Appropriate 
Diagnostic Information)

2. Worn, scuffed or broken rings. 2. Hone cylinder bores. Install 

new rings.

3. Carbon in oil ring slots.

3. Clean pistons and 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(s).

6. Valve stem seal(s) worn or 
damaged.

6. Replace seal(s).

WARNING:

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

 

2007 Dodge Nitro R/T 

2007 ENGINE 4.0L - Service Information - Nitro

  

testing, listen for pressurized air escaping through the throttle body, tailpipe and oil filler cap opening. 
Check for bubbles in the coolant.  

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

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

maintained in the cylinder.  

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, see 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.  

ENGINE PERFORMANCE 

CONDITION 

POSSIBLE CAUSE 

CORRECTION 

ENGINE WILL NOT START

1. Weak battery.

1. Test battery. Charge or replace 
as necessary. Refer to 
DESCRIPTION .

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 

 

2007 Dodge Nitro R/T 

2007 ENGINE 4.0L - Service Information - Nitro

  

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. Check and adjust gap as needed.

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 
or a loose camshaft sprocket.

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 gasket, 
manifold, and vacuum hoses.

4. Faulty coil(s).

4. Test and replace as necessary. 
(Refer to Appropriate Diagnostic 
Information)

ENGINE LOSS OF POWER

1. Dirty or incorrectly gapped 
plugs.

1. Set gap as needed or replace 
plug(s).

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 as needed.

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. Check exhaust system 
restriction. Replace parts, as 
necessary.

9. Faulty 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. Set gap as needed or replace 
plug(s).

2. Contamination in Fuel System. 2. Clean fuel system and replace 

fuel filter.

 

2007 Dodge Nitro R/T 

2007 ENGINE 4.0L - Service Information - Nitro