ENGINE COMPRESSION
| Application | Specification | |
|---|---|---|
| Compression Ratio | ||
| 2.5L | 9.2:1 | |
| 4.0L | 8.8:1 | |
| 4.2L | 8.6:1 | |
| 5.9L | 8.25:1 | |
COMPRESSION SPECIFICATIONS
Note. Specifications for compression pressure and cylinder pressure variation are not available from the manufacturer.
VALVE CLEARANCE
Note. All models are equipped with hydraulic lifters which should be adjusted to zero lash.
2.5L
E-I-I-E-E-I-I-E (Front-to-Rear).
4.0 & 4.2L
E-I-I-E-I-E-E-I-E-I-I-E (Front-to-Rear)
5.9L
Both Banks - E-I-I-E-E-I-I-E (Front-to-Rear).
IGNITION COIL
| Application | Primary Ohms | Secondary Ohms |
|---|---|---|
| All | 1.13-1.23 | 7700-9300 |
IGNITION COIL RESISTANCE
HIGH TENSION WIRE RESISTANCE
| Application | Minimum Ohms | Maximum Ohms |
|---|---|---|
| All Wires | 250 per inch | 1000 per inch |
HIGH TENSION WIRE RESISTANCE
SPARK PLUGS
| Application | Champion |
|---|---|
| 2.5L | RC-12 LYC |
| 4.0L | RC-9 YC |
| 4.2L | RFN-14 LY |
| 5.9L | RN-12 YC |
SPARK PLUG TYPE
| Application | Gap: In. (mm) | Torque: Ft. Lbs. (N.m) |
|---|---|---|
| 2.5L, 4.0L & 4.2L | .035 (.89) | 27 (36.61) |
| 5.9L | .033 (.84) | 27 (36.61) |
SPARK PLUG SPECIFICATIONS
Scheme 1
Scheme 2
Scheme 3
DISTRIBUTOR
Some models (TBI & MPFI) are equipped with a Renix solid state ignition module. Renix system uses a TDC sensor mounted near the flywheel. The distributor consists of a cap and rotor. Its only function is to distribute high voltage to appropriate spark plug. No adjustments are required on either unit.
IGNITION TIMING
Note. No adjustment is possible on models with Renix ignition.
2.5L 4-Cyl. TBI
Timing and fast idle are not adjustable.
4.0L 6-Cyl. MPFI
Timing and fast idle are not adjustable.
4.2L 6-Cyl. 2-Bbl.
Use emission control label in engine compartment.
5.9L V8 2-Bbl.
Use emission control label in engine compartment.
FUEL PUMP
Note. Fuel pump performance is a measurement of fuel pressure and volume availability, not regulated fuel pressure.
| Application | Psi (kg/cm 2 ) | |
|---|---|---|
| Carbureted Vehicles | ||
| 4.2L | 4-5 (0.28-0.35) | |
| 5.9L | 5-6.5 (0.35-0.46) | |
| Injected Vehicles | ||
| 2.5L TBI | 14-15 (0.98-1.06) | |
| 4.0L MPFI | 31 (2.18) | |
FUEL PUMP PERFORMANCE
PUMP DELIVERY
Fuel pump should deliver 1 pt. (0.47L) in 30 seconds.
IDLE SPEED & MIXTURE
Note. On vehicles with fuel injection, idle mixture is controlled by the Electronic Control Module (ECM). Idle mixture adjustment is not required or possible on fuel injected models. On carbureted models, mixture should be adjusted only if vehicle fails emission testing or carburetor has been disassembled.
Note. Ensure idle speed and timing are set prior to adjusting idle mixture. If mixture adjustment exceeds 3 minutes, run engine at 2000 RPM in NEUTRAL for one minute, and resume adjustment.
| Application | RPM | |
|---|---|---|
| 4.2L | ||
| Curb Idle | (1) 680 (50 State) | |
| Idle Drop | 50 | |
| 5.9L | ||
| Curb Idle | 600 | |
| Idle Drop | 20 | |
| (1) 700 RPM (High Altitude) | ||
| (1) | 700 RPM (High Altitude) |
CURB IDLE & IDLE DROP
Note. If final RPM differs more than 30 RPM from specified curb idle, reset curb idle, and repeat mixture adjustment.
FAST (COLD) IDLE SPEED (CARBURETED)
| Application | RPM |
|---|---|
| 4.2L | 1700 |
| 5.9L | 1600 |
FAST IDLE SPECIFICATIONS
SENSOR READING (2.5L, 4.0L & 4.2L)
Output voltage reading of TPS should be .825-.835 volts (.830 volts is ideal).