Turn off ignition, disconnect battery, detach wiring harness from ignition coil. Check terminals for dirt, corrosion, damage. Use ohmmeter to measure resistance between terminals: 2.3L engines B+ to Coil 1, B+ to Coil 2 or 3, B+ to Coil 4. 4.DL engines B+ to Coil 1, 2, 3. Resistance should be 0.3-1.0 ohms. If not, replace coil. Measure resistance between coil terminals and spark plug wire towers. If 6,500-11,500 ohms, coils are OK. If not, replace coil pack. On 2.3L engines, if one pack is bad, other doesn't need replacing. 4.0L engine has one pack with three coils. Disconnect battery, unplug harness from coil pack. Remove spark plug wires, screws, and coil pack. Install new pack, tighten screws. Apply dielectric compound to spark plug boots. Attach wires and battery.