Jeep Cherokee

 Service Manual

Ignition system » Removal and installation
Spark plugs

PLUG REMOVAL

On the 4.0L 6-cylinder engine the spark plugs are located below the coil rail assembly. To gain access to any/all spark plug(s), refer to Ignition Coil-4.0L Engine Removal/Installation.

Fig. 18 Cable Removal

1 - SPARK PLUG CABLE AND BOOT
2 - SPARK PLUG BOOT PULLER
3 - TWIST AND PULL
4 - SPARK PLUG

(1) 2.5L 4-Cylinder Engine: Always remove spark plug or ignition coil cables by grasping at the cable boot (Fig. 18). Turn the cable boot 1/2 turn and pull straight back in a steady motion. Never pull directly on the cable. Internal damage to cable will result.

(2) Prior to removing the spark plug, spray compressed air around the spark plug hole and the area around the spark plug. This will help prevent foreign material from entering the combustion chamber.

(3) Remove the spark plug using a quality socket with a rubber or foam insert.

(4) Inspect the spark plug condition. Refer to Spark Plugs Conditions.

PLUG CLEANING

The plugs may be cleaned using commercially available spark plug cleaning equipment. After cleaning, file the center electrode flat with a small point file or jewelers file before adjusting gap.

CAUTION: Never use a motorized wire wheel brush to clean the spark plugs. Metallic deposits will remain on the spark plug insulator and will cause plug misfire.

PLUG GAP ADJUSTMENT

Check the spark plug gap with a gap gauge tool. If the gap is not correct, adjust it by bending the ground electrode (Fig. 19). Never attempt to adjust the gap by bending the center electrode.

Fig. 19 Setting Spark Plug Gap-Typical

1 - GAUGE
2 - SPARK PLUG

SPARK PLUG GAP

•  2.5L 4-Cylinder Engine Spark Plug Gap:.89 mm (.035 in).
•  4.0L 6-Cylinder Engine Spark Plug Gap:.89 mm (.035 in).

PLUG INSTALLATION

Always tighten spark plugs to the specified torque.

Over tightening can cause distortion. This may result in a change in the spark plug gap, or a cracked porcelain insulator.

When replacing the spark plug and ignition coil cables, route the cables correctly and secure them in the appropriate retainers. Failure to route the cables properly can cause the radio to reproduce ignition noise. It could cause cross ignition of the spark plugs, or short circuit the cables to ground.

(1) Start the spark plug into the cylinder head by hand to avoid cross threading.

(2) Tighten the spark plugs to 35-41 N·m (26-30 ft.

lbs.) torque.

(3) 2.5L 4-Cylinder Engine: Install spark plug cables over spark plugs.

(4) 4.0L 6-Cylinder Engine: Install coil rail. Refer to Ignition Coil-4.0L Engine Removal/Installation.

Spark plug cables

Spark plugs

Ignition coil-2.5L engine

Ignition coil-4.0L engine

Crankshaft position (CKP) sensor

Camshaft position sensor-2.5L engine

Camshaft position sensor-4.0L engine

Distributor-2.5L engine

Ignition switch and key cylinder

Shifter/ignition interlock