ENGINE COMPRESSION
Check engine compression with engine at normal operating temperature, all spark plugs removed and throttle wide open.
| Application | Specification | |
|---|---|---|
| Compression Ratio | ||
| 2.5L | 9.1:1 | |
| 4.0L | 8.7:1 | |
| 4.7L | 9.0:1 | |
| Compression Pressure | ||
| Normal | 120-150 psi (8.3-10.5 kg/cm 2 ) | |
| Maximum Variation Between Cylinders (1) | 30 psi (2.1 kg/cm 2 ) | |
| (1) Manufacturer does not provide information for 5.2L or 5.9L. | ||
| (1) | Manufacturer does not provide information for 5.2L or 5.9L. |
COMPRESSION SPECIFICATIONS
VALVE CLEARANCE
Note. All models are equipped with hydraulic lifters. No adjustments are required.
IGNITION COIL
| Application | Primary | Secondary | |
|---|---|---|---|
| Cherokee & Wrangler | |||
| Diamond Coil | .96-1.18 | 11,300-15,300 | |
| Toyodenso Coil | .95-1.20 | 11,300-13,300 | |
| Grand Cherokee | |||
| 4.0L Engine | .71-.88 | (1) | |
| 4.7L Engine | .6-.9 | 6000-9000 | |
| (1) Secondary resistance cannot be checked using an ohmmeter. | |||
| (1) | Secondary resistance cannot be checked using an ohmmeter. |
IGNITION COIL RESISTANCE - Ohms @ 70-80°F (21-27°C)
HIGH TENSION WIRE RESISTANCE
| Application | Ohms Per Inch |
|---|---|
| All Wires | 250-1000 |
HIGH TENSION WIRE RESISTANCE
SPARK PLUGS
| Application | Specification |
|---|---|
| 2.5L & 4.0L | Champion RC-12ECC |
| 4.7L | Champion RC-12MCC4 |
SPARK PLUG TYPE
| Application | Gap In. (mm) | Torque Ft. Lbs. (N.m) |
|---|---|---|
| 2.5L & 4.0L | .035 (.89) | 26-30 (35-41) |
| 4.7L | .040 (1.01) | 30 (41) |
SPARK PLUG SPECIFICATIONS
Scheme 1
Scheme 2
Scheme 3
IGNITION TIMING
All models are equipped with Powertrain Control Module (PCM) computerized ignition. PCM controls ignition timing. DO NOT move distributor in an attempt to adjust timing, no timing adjustment is possible.
FUEL PUMP
Note. Fuel pump performance refers to regulated fuel pressure and volume availability. Mechanical fuel pressure regulator is part of fuel pump module and is not controlled by vacuum or PCM.
| Application | Pressure psi (kg/cm 2 ) | (1) Min. Vol. In 7 Sec. |
|---|---|---|
| All Models | 44.2-54.2 (3.1-3.7) | .5 Pt. (.25L) |
| (1) DO NOT operate fuel pump longer than 7 seconds. | ||
| (1) | DO NOT operate fuel pump longer than 7 seconds. |
FUEL PUMP PERFORMANCE
INJECTOR RESISTANCE
| Application | Specification |
|---|---|
| All Models | 10.8-13.2 |
INJECTOR RESISTANCE - Ohms @ 68°F (20°C)
IDLE SPEED & MIXTURE
Note. Idle speed and mixture are controlled by the Powertrain Control Module (PCM). Adjustment is not required or possible.
Cherokee & Wrangler
Output voltage (center terminal of TP sensor) should be more than .26 volt, but less than .95 volt at closed throttle (idle) and less than 4.49 volts at WOT. Voltage should increase gradually and smoothly as throttle is slowly opened from idle to WOT. TP sensor is not adjustable.
Grand Cherokee
Output voltage (center terminal of TP sensor) should be .92 volt or less at closed throttle (against throttle stop). Voltage should increase gradually and smoothly as throttle is slowly opened from idle to WOT. TP sensor is not adjustable.