2007 ENGINE
3.7L - Service Information - Nitro
DESCRIPTION
3.7L ENGINE DESCRIPTION
Fig. 1: 3.7L Engine
Courtesy of CHRYSLER LLC
The 3.7 liter (226 CID) six-cylinder engine is an 90° single overhead camshaft engine. The cast iron cylinder
block is made up of two different components; the first component is the cylinder bore and upper block, the
2007 Dodge Nitro R/T
2007 ENGINE 3.7L - Service Information - Nitro
2007 Dodge Nitro R/T
2007 ENGINE 3.7L - Service Information - Nitro
second component is the bedplate that comprises the lower portion of the cylinder block and houses the lower
half of the crankshaft main bearings. The cylinders are numbered from front to rear with the left bank being
numbered 1, 3, and 5 and the right bank being numbered 2, 4, and 6. The firing order is 1-6-5-4-3-2. The engine
serial number is located at the right front side of the engine block. See Fig. 1 .
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 FUEL DELIVERY - GAS ).
5. Remove the ASD relay. Refer to 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. See SPECIFICATIONS for the correct engine compression pressures.
ENGINE MECHANICAL DIAGNOSTIC TABLE
CONDITION POSSIBLE CAUSES CORRECTIONS
NOISY VALVES 1. High or low oil level in
crankcase.
1. Refer to 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. Clean or replace as necessary.
5. Worn rocker arms. 5. Replace as necessary.
6. Worn valve guides. 6. See STANDARD
PROCEDURE .
7. Excessive runout of valve
seats.
7. Service valves and valve seats.
See STANDARD PROCEDURE .
ENGINE VIBRATION 1. Counter Balance Shaft not
timed properly
1. Refer to Engine Timing in this
article
CONNECTING ROD NOISE 1. Insufficient oil supply. 1. Refer to SPECIFICATIONS .
2. Low oil pressure. 2. Check oil pump, if Ok, check rod
and main bearings for excessive
2007 Dodge Nitro R/T
2007 ENGINE 3.7L - Service Information - Nitro
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).
See ENGINE PERFORMANCE DIAGNOSTIC TABLE and ENGINE MECHANICAL DIAGNOSTIC
TABLE for possible causes and corrections of malfunctions. Refer to DIAGNOSIS AND TESTING .
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:
Cylinder Compression Pressure Test. See DIAGNOSIS AND TESTING .
Cylinder Combustion Pressure Leakage Test. See DIAGNOSIS AND TESTING .
Engine Cylinder Head Gasket Failure Diagnosis. See DIAGNOSIS AND TESTING .
Intake Manifold Leakage Diagnosis. See 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:
Exhaust and intake valve leaks (improper seating).
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 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
2007 Dodge Nitro R/T
2007 ENGINE 3.7L - Service Information - Nitro
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 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.
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 step CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART .
CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART
ENGINE LUBRICATION DIAGNOSTIC TABLE
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
2007 Dodge Nitro R/T
2007 ENGINE 3.7L - Service Information - Nitro
ENGINE PERFORMANCE DIAGNOSTIC TABLE
CONDITION POSSIBLE CAUSES CORRECTION
OIL LEAKS 1. Gaskets and O-Rings. -
(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. See
REMOVAL .
3. Crankshaft seal flange.
Scratched, nicked or grooved.
3. Polish or replace crankshaft.
4. Oil pan flange cracked. 4. Replace oil pan. See
REMOVAL .
5. Timing chain cover seal
damaged.
5. Re-seal timing cover.
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. See
REMOVAL .
3. Low oil pressure. 3. Check oil pump and bearing
clearance.
4. Clogged oil filter. 4. Replace oil filter. See
REMOVAL .
5. Worn oil pump. 5. Replace oil pump. See
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. See
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. See
STANDARD PROCEDURE .
3. Incorrect ring size installed. 3. Replace rings. See
STANDARD PROCEDURE .
4. Worn valve guides. 4. Ream guides and replace
valves. See STANDARD
PROCEDURE .
5. Leaking valve guide seals. 5. Replace valve guide seals.
CONDITION POSSIBLE CORRECTION
2007 Dodge Nitro R/T
2007 ENGINE 3.7L - Service Information - Nitro
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Description
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