Jeep Engines - Oljeep

238 MOPAR PERFORMANCE PARTSINTRODUCTIONIgnitionNote: Some newer 4.0L Power Tech engines (modelspecific -check your service manual) use a distributor-lessignition system. For information on this system, refer toDistributorless Ignition System, later in this section.For any type of racing, a good electronic ignition system isa must. The Mopar Performance Parts Chrome Box IgnitionControl Module (P4120534) is perfect for those of youracing low to moderately high performance engines. Forextreme high performance, the Super Gold ICM(P4120600) is the preferred choice.The area of ignition systems and components has beenchanging rapidly in the last few years. Further developmentis expected to continue well into the future, providing Jeepracers with the best high performance ignition systemsavailable for their race vehicles.Older ignition systems, such as point-type, will not becovered because we no longer produce or recommend thesepieces for high performance race vehicles. We will try tocover all the new electrical modifications, systems andhardware that have been developed recently for racevehicle use.Ignition EnergyThe purpose of the ignition system on an internal combustionengine is to start the combustion of the fuel/air mixture. Itmust ignite a flame that will be self-sustaining and it mustignite it at the proper time so that combustion will becompleted at the proper time for best engine efficiency.One way of comparing ignition systems is by the amount ofenergy that they can deliver to the spark plug. There areseveral different types of energy “curves.” The two mostimportant characteristics are peak energy and duration(time). Capacitive-discharge systems tend to have very highpeak energy but very short duration. Multi-fire systemshave long durations and fire the plug several times perrevolution. Chrysler-Plymouth-Dodge-Jeep ignitionsystems, such as the Super Gold ICM (P4120600), featurehigh peak energy, long duration, and one of the highest totalenergies (area under the curve) delivered to the plugbecause they don’t go to zero during their duration in aneffort to fire the plug more than once. Race engines needhigh total energy systems to deliver maximum power,especially at high rpm.Variations in fuel composition, air-to-fuel ratio,distribution, internal turbulence in the cylinder, andcombustion chamber shape are a few of the factors that canmake the combustion process less than ideal. They all havethe common characteristic that poor fuel burning mayresult. The factors mentioned produce effects that, althoughSystemthey can’t be corrected by a more powerful ignition system,may be overcome by one. In other words, an ignitionsystem will not change these factors (aidfuel ratio,turbulence, etc.), but the proper system can cause ignitionof the mixture in spite of their presence. A productionsystem is called on to do this to some extent; however, asmore severe requirements are placed on the engine, theproduction system will quickly reach its limit.A general rule of thumb is that at least 30 millijoules ofenergy are required to ignite the typical mixture. Mostsystems exceed this amount (even production systems) inthe lower rpm ranges. However, this is for a typicalcondition. As more performance and higher speeds aredemanded of an engine, these conditions are no longer true.There are many indications that a stronger spark is needed.Many replacement systems are available that try to answersome of these requirements.With some of the less than ideal mixture conditionsmentioned, there will be times when the mixture is notignitable no matter how much energy is pumped into thespark plug. Multiple Spark Discharge is the answer to theproblem. It not only produces a very strong first spark, butit also repeats this spark. This is important because if thelack of ignition is caused by such things as turbulence ornon-uniform distribution of the mixture in the cylinder, theneventually an ignitable mixture will be available in theregion of the plug. One of the MSD repetitive sparks willignite the mixture.ELECTRONIC IGNITION SYSTEMThe 4.0L engine is a multi-point fuel injected engine. Theelectronic ignition system used consists of the followingcomponents:A solid-state Ignition Control Module (ICM) togenerate the voltage for spark plug firingAn Powertrain Control Module (PCM) to process inputinformation to fire the ICMAn engine speed sensor with flywheel trigger to inputcrankshaft position for the PCMA synchronization pulse (stator) for firing order inputto the PCMNote: Ignition timing (advancehetard) is controlled by thePClM and is not adjustable.