ENGINE - 3.7L - SERVICE INFORMATION
DESCRIPTION
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 cylinderbore and upper block, the second com-
ponent is the bedplate that comprises the lower portion of the cylinder block and houses the lower half of the crank-
shaft main bearings. The cylinders are numbered from front to rear with theleft 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.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - ENGINE DIAGNOSIS - INTRODUCTION
Engine diagnosis is helpful in determining the causes of malfunctions notdetected and remedied by routine main-
tenance.
These malfunctions may be classified as either performance (e.g., engineidles rough and stalls) or mechanical
(e.g., a strange noise).
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.
CONDITION POSSIBLE CAUSES CORRECTION
OIL PUMPING AT RINGS; SPARK
PLUGS FOULING1. 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 compressionpressure test can be utilized to diagnose several engine malfunctions.
Ensurethebatteryiscompletelychargedandtheenginestartermotorisingood 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 SHUTDOWNRELAY-
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 - CYLINDERCOMBUSTION 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).
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 radiatorcap.
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 BODYIntake valve bent, burnt, or not
seated properlyInspect valve and valve seat.
Reface or replace, as necessary.
Inspect valve springs. Replace as
necessary.
AIR ESCAPES THROUGH
TAILPIPEExhaust valve bent, burnt, or not
seated properlyInspect valve and valve seat.
Reface or replace, as necessary.
Inspect valve springs. Replace as
necessary.
AIR ESCAPES THROUGH
RADIATORHead gasket leaking or cracked
cylinder head or blockRemove cylinder head and inspect.
Replace defective part
MORE THAN 50% LEAKAGE
FROM ADJACENT CYLINDERSHead gasket leaking or crack in
cylinder head or block between
adjacent cylindersRemove cylinder head and inspect.
Replace gasket, head, or block as
necessary
MORE THAN 25% LEAKAGE AND
AIR ESCAPES THROUGH OIL
FILLER CAP OPENING ONLYStuckorbrokenpistonrings;
cracked piston; worn rings and/or
cylinder wallInspect for broken rings or piston.
Measure ring gap and cylinder
diameter, taper and out-of-round.
Replace defective part as necessary
STANDARD PROCEDURE
STANDARD PROCEDURE - REPAIR DAMAGED OR WORN THREADS
CAUTION: Be sure that the tapped holes maintain the original center line.
Damaged or worn threads can be repaired. Essentially, this repair consistsof:
Drilling out worn or damaged threads.
Tapping the hole with a special Heli-Coil Tap, or equivalent.
Installing an insert into the tapped hole to bring the hole back to its original thread size.
STANDARD PROCEDURE - FORM-IN-PLACE GASKETS AND SEALERS
There are numerous places where form-in-place gaskets are used on the engine. Care must be taken when apply-
ing form-in-place gaskets to assure obtaining the desired results.Do not use form-in-place gasket material
unless specified.Bead size, continuity, and location are of great importance. Too thin a bead can result in leakage
while too much can result in spill-overwhich can break off and obstruct fluid feed lines. A continuous bead of the
proper width is essential to obtain a leak-free gasket.
There are numerous types of form-in-place gasket materials that are used in the engine area. Mopar
Engine RTV
GEN II, Mopar
ATF-RTV, and MoparGasket Maker gasket materials, each have different properties and can not
be used in place of the other.
MOPAR
ENGINE RTV GEN II
Mopar
Engine RTV GEN II is used to seal components exposed to engine oil. This material is a specially designed
black silicone rubber RTV that retains adhesion and sealing properties when exposed to engine oil. Moisture in the
air causes the material to cure. This material is available in three ounce tubes and has a shelf life of one year. After
one year this material will not properly cure. Always inspect the package for the expiration date before use.
MOPAR
AT F R T V
Mopar
ATF RTV is a specifically designed black silicone rubber RTV that retains adhesion and sealing properties
to seal components exposed to automatic transmission fluid, engine coolants, and moisture. This material is avail-
able in three ounce tubes and has a shelf life of one year. After one year thismaterial will not properly cure. Always
inspect the package for the expiration date before use.
MOPAR
GASKET MAKER
MoparGasket Maker is an anaerobic type gasket material. The material cures in the absence of air when
squeezed between two metallic surfaces. It will not cure if left in the uncovered tube. The anaerobic material is for
use between two machined surfaces. Do not use on flexible metal flanges.
MOPAR
GASKET SEALANT
Mopar
Gasket Sealant is a slow drying, permanently soft sealer. This material isrecommended for sealing
threaded fittings and gaskets against leakage of oil and coolant. Can be used on threaded and machined parts
under all temperatures. This material is used on engines with multi-layersteel (MLS) cylinder head gaskets. This
material also will prevent corrosion. Mopar
Gasket Sealant is available in a 13 oz. aerosol can or 4oz./16 oz. can
w/applicator.
FORM-IN-PLACE GASKET AND SEALER APPLICATION
Assembling parts using a form-in-place gasket requires care but it’s easier than using precut gaskets.
Mopar
Gasket Maker material should be applied sparingly 1 mm (0.040 in.) diameter or less of sealant to one
gasket surface. Be certain the material surrounds each mounting hole. Excess material can easily be wiped off.
Components should be torqued in place within 15 minutes. The use of a locating dowel is recommended during
assembly to prevent smearing material off the location.
Mopar
Engine RTV GEN II or ATF RTV gasket material should be applied in a continuous bead approximately 3
mm (0.120 in.) in diameter. All mounting holes must be circled. For corner sealing, a 3.17 or 6.35 mm (1/8 or 1/4 in.)
drop is placed in the center of the gasket contact area. Uncured sealant maybe removed with a shop towel. Com-
ponents should be torqued in place while the sealant is still wet to the touch (within 10 minutes). The usage of a
locating dowel is recommended during assembly to prevent smearing material off the location.
Mopar
Gasket Sealant in an aerosol can should be applied using a thin, even coat sprayed completely over both
surfaces to be joined, and both sides of a gasket. Then proceed with assembly. Material in a can w/applicator can
be brushed on evenly over the sealing surfaces. Material in an aerosol can shouldbeusedonengineswithmulti-
layer steel gaskets.
STANDARD PROCEDURE - ENGINE GASKET SURFACE PREPARATION
To ensure engine gasket sealing, proper surface prep-
aration must be performed, especially with the use of
aluminum engine components and multi-layer steel
cylinder head gaskets.
Neveruse the following to clean gasket surfaces:
Metal scraper (3).
Abrasive pad (1) or paper to clean cylinder block
and head.
High speed power tool (1) with an abrasive pad
orawirebrush.
NOTE: Multi-Layer Steel (MLS) head gaskets
require a scratch free sealing surface.
Only use the following for cleaning gasket surfaces:
Solvent or a commercially available gasket
remover
Plastic or wood scraper.
Drill motor with 3M Roloc™ Bristle Disc (white or yellow).
CAUTION: Excessive pressure or high RPM (beyond the recommended speed), can damage the sealing sur-
faces. The mild (white, 120 grit) bristle disc is recommended. If necessary, the medium (yellow, 80 grit) bris-
tle disc may be used on cast iron surfaces with care.
31. Disconnect crankshaft postion sensor.
32. Disconnect the engine block heater power cable, if equipped.
33. Disconnect the front propshaft at the front differ-
ential and secure out of way.
NOTE: It is necessary to disconnect the front
propshaft for access to the starter and left side
exhaust flange.
34. Remove the starter (4).
35. Remove the ground straps from the left (2) and
right (3) side of the block.
36. Disconnect the right and left exhaust pipes at the
manifolds and from the crossover, and remove
from the vehicle.
NOTE: The exhaust clamps at the manifolds can-
not be reused. New clamps must be used or leaks
may occur.
37. Remove the structural cover .
38. Remove torque convertor bolts, and mark location
for reassembly.
39. Remove transmission bellhousing to engine bolts.
40. Remove left and right engine mount thru bolts.
41. Lower the vehicle.
42. Support the transmission with a suitable jack.
43. Connect a suitable engine hoist to the engine lift
plate.
44. Remove engine from vehicle.
8. Install the starter (4).
9. Connect the crankshaft position sensor.
10. Install the engine block heater power cable, if
equipped.
CAUTION: The structural cover requires a specific
torque sequence. Failure to follow this sequence
may cause severe damage to the cover.
11. Install the structural cover.
NOTE: New clamps must be used on exhaust man-
ifold flanges. Failure to use new clamps may
result in exhaust leaks.
12. Install the left and right exhaust pipes.
13. Connect the left and right oxygen sensors.
14. Lower vehicle.
15. Remove the engine lift plate.
16. Connect the knock sensors.
17. Connect the engine to body ground straps at the
left side of the cowl.
18. Install the intake manifold.
19. Install the engine oil dipstick tube.
20. Install the power brake booster vacuum hose.
21. Install the breather hoses.
22. Install the PCV hose.
23. Install the fuel rail.
24. Install the coil over plugs.