Old Sparky

Words By: Mark Yanochko

Ignition systems have benefited greatly from the use of electronics. The net result is a hotter, cleaner spark to ignite the air/fuel mixture. That not only results in better performance, but fewer emissions as well. Spark plugs last longer these days (often more than 100,000 miles), but the increased heat in the engine compartment can take a toll on the ignition wires and other components. Also, physical damage, such as cracks in the ceramic, can cause problems with spark plugs.

There are two different ignition systems being used on Chrysler vehicles: (1) the coil, wire and spark plug and (2) the coil-on-plug, which does not use a traditional spark plug wire. To keep your ignition system in tip-top shape, let’s review inspection and component replacement for both plugs and wires.

Coil, Wires and Plugs

The coil, wire, plug system uses an ignition coil and several plug wires (depending on the number of cylinders) that deliver the electrical charge to each spark plug. Figure 1 shows the coil, A, and two of the spark plug wires, B, on a 4-cylinder engine. The plug wire should be inspected for any cracks in the insulation (this is detailed in the Diagnostics on page 48).

Remove the spark plug wire by grabbing the boot, rotating it 1/2 turn and pulling straight back in a steady motion. Before you remove the spark plug, clean the area around the plug, preferably with compressed air, to remove any dirt that could fall into the plug hole. Using a quality socket with a foam insert and a ratchet, C, remove the spark plug (see Figure 2).

A clean burning plug, D, will have a light brown color. Figure 3 shows such a plug compared to a new one, E. Deposits of oil indicate a serious oil leak problem, perhaps past the piston rings. A compression test will verify this problem. Heavy carbon deposits can indicate an air/fuel mixture problem.

When replacing plug wires and plugs, be sure to route the wires correctly and secure the wires in the appropriate retainers. Failure to do so can cause radio ignition noise or short circuit the wires to ground.

Use a feeler gauge, F, to accurately set the electrode gap on the new plug, G, as shown in Figure 4, if it has a flat tip electrode. If the plug has a platinum electrode, use a tapered gauge. Avoid cross-threading the plug and do not over tighten. Fit the boot of the wire onto the spark plug. A click will be heard when the wire properly attaches to the plug.

Coil-on-Plug

Many vehicles use the coil-on-plug ignition system. With this design, each plug has its own ignition coil, H. A wire connector, J, is plugged into the side of the coil, and the coil is held in place with one or two retaining screws, K (see Figure 5). A rubber sleeve extends from the bottom side of the coil to the spark plug. Within this sleeve is a thin wire coil spring that transmits the current from the coil to the plug. Although the assembly can be taken apart, it is only serviceable as a complete unit.

On V-type engines, one bank of the vee will be exposed with coil and plug service being relatively easy. The coils and plugs on the opposite bank will probably be blocked by the intake manifold. This requires the removal of the intake manifold.

Removal of the coil assembly is straightforward. Remove the retaining screw(s), L, that secures the coil, M, in place (see Figure 6). Then, disconnect the electrical connector, N, as shown in Figure 7. Finally, pull the coil/sleeve assembly, O, from the spark plug hole (see Figure 8). Remove the plug with a socket and ratchet as shown in Figure 2.

Inspect the spark plug (see Figure 3). Also, inspect the connector for any damage. This is true, too, for the coil, which is exposed to extreme heat. This can lead to cracking and stress cracks.

Coil-on-plug ignition systems use platinum tip electrodes. Use a tapered gauge to set the electrode gap, not a feeler gauge. Follow the same installation tips for these plugs as described above. However, you should also apply anti-seize compound to the plug threads. Install the coil/sleeve assembly, connect the electrical connector and insert the retaining screw(s) to finish the job.