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TU NE-U P - 6 -C YL
1988 J e ep C hero ke e
1987-88 TUNE-UP
Jeep 6 Cylinder Tune-Up
Cherokee, Comanche, Wagoneer, Wrangler
IDENTIFICATION
ENGINE IDENTIFICATION
Engine can be identified by the fourth character of engine
Build Date Code number, located on a tag attached to right side of
block between No. 2 and 3 cylinders.
The same code letter is also the fourth character in the
Vehicle Identification Number (VIN), located at top left corner of
dashboard.
ENGINE CODE TABLE
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Engine Code
4.0L (242") MPFI ....................................... M
4.2L (258") 2-Bbl. ..................................... C
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TUNE-UP NOTES
NOTE: When performing tune-up procedures described in this
article, these notes and precautions must be followed.
Due to late changes and corrections, always refer to Emission
Control Label in engine compartment before attempting tune-up. If
manual and label specifications differ, use label specifications.
When performing tune-up on vehicles equipped with a catalytic
converter, do not allow or create an engine misfire in one or more
cylinders for an extended period of time. Damage to converter from
overheating may occur due to loading with unburned fuel.
TESTING
ENGINE COMPRESSION
Check compression pressure with engine at normal operating
temperature, all spark plugs removed, throttle and choke valves wide
open and engine at cranking speed.
COMPRESSION SPECIFICATIONS TABLE
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Application Specification
Compression Ratio .................................. 9.2:1
Compression Pressure ....... 120-150 psi (8.4-10.5 kg/cm
)
Maximum Variation Between Cylinders .. 30 psi (2.1 kg/cm) \
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HIGH TENSION WIRE RESISTANCE
Do not puncture spark plug wires with any type of probe.
Remove spark plug wire and check resistance using an ohmmeter.
