ENGINE COMPRESSION
Check engine compression with engine at normal operating temperature, all spark plugs removed and throttle wide open.
| Application | Psi (kg/cm 2 ) | |
|---|---|---|
| Normal Compression Pressure | ||
| 2.5L & 4.0L | 120-150 (8.3-10.5) | |
| 4.7L | 140-180 (9.8-12.7) | |
| Maximum Variation Between Cylinders | ||
| 2.5L & 4.0L | 30 (2.1) | |
| 4.7L | (1) | |
| (1) Information is not available from manufacturer. | ||
| (1) | Information is not available from manufacturer. |
COMPRESSION SPECIFICATIONS
VALVE CLEARANCE
Note. All models are equipped with hydraulic lifters. No adjustments are required.
IGNITION COIL
| Application | Primary | Secondary | |
|---|---|---|---|
| 2.5L | |||
| Diamond Coil | .97-1.18 | 11,300-15,300 | |
| Toyodenso Coil | .95-1.20 | 11,300-13,300 | |
| 4.0L | .71-.88 | (1) | |
| 4.7L | .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 RC12ECC |
| 4.7L | Champion RC12MCC4 |
SPARK PLUG TYPE
| Application | Gap - In. (mm) | Torque - Ft. Lbs. (N.m) |
|---|---|---|
| 2.5L & 4.0L | .035 (.89) | 30 (41) |
| 4.7L | .040 (1.01) | 30 (41) |
SPARK PLUG SPECIFICATIONS
FIRING ORDER
Note. To identify firing order, refer to illustrations. (Scheme 1)- (Scheme 3).
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 attempt to adjust ignition timing by rotating distributor (2.5L) or oil pump drive shaft assembly (4.0L). If distributor or oil pump drive is rotated or replaced, fuel system synchronization will be changed. To synchronize fuel system, see FUEL SYSTEM SYNCHRONIZATION under FUEL SYSTEMS in ON-VEHICLE ADJUSTMENTS article.
FUEL PUMP
Note. Fuel pump performance refers to regulated fuel pressure and volume availability. Mechanical fuel filter/pressure regulator is not controlled by vacuum or Powertrain Control Module (PCM). On Cherokee and Wrangler, fuel filter/pressure regulator is part of fuel pump module mounted in top of fuel tank. On Grand Cherokee, fuel filter/pressure regulator is located in front of fuel tank, above rear axle.
| Application | Pressure - psi (kg/cm 2 ) | (2) Min. Vol. In 7 Sec. |
|---|---|---|
| All Models | 44.2-54.2 (3.1-3.7) | .5 Pt. (.25L) |
| (1) Fuel pressure is measured with engine idling. (2) DO NOT operate fuel pump longer than 7 seconds when checking pump volume. Fuel pump module reservoir may run empty. | ||
| (1) | Fuel pressure is measured with engine idling. |
| (2) | DO NOT operate fuel pump longer than 7 seconds when checking pump volume. Fuel pump module reservoir may run empty. |
FUEL PUMP PERFORMANCE (1)
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.
THROTTLE BODY MINIMUM AIRFLOW IDLE SPEED
| Application | RPM |
|---|---|
| All Models | 500-900 |
| (1) See CHECKING MINIMUM AIRFLOW under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING article for test procedure. | |
| (1) | See CHECKING MINIMUM AIRFLOW under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING article for test procedure. |
MINIMUM AIRFLOW (1)
THROTTLE POSITION (TP) SENSOR
Output voltage (center terminal of TP sensor) should be approximately .96 volt at closed throttle (idle) and approximately 4.49 volts at Wide Open Throttle (WOT). Voltage should increase gradually and smoothly as throttle is slowly opened from idle to WOT. TP sensor is not adjustable. Closed throttle (idle) TP sensor voltage is a "learned" Powertrain Control Module (PCM) function.