Jeep Engines - Oljeep

T - T l328 MOPAR PERFORMANCE PARTSThe Micro-Computer Unit (MCU) controls ignition coiloperation through the ignition module. The MCU processesthe ignition signals it receives and then sends a signal to theignition module. The ignition module then interrupts theprimary circuit to the ignition coil causing spark to occur.Dwell is adjusted automatically.Note: When disconnecting SSI system connectors, pullthem apart with a firm, straight pull. DO NOT attempt to prythem apart with a screwdriver. When connecting them, presstogether firmly to overcome hydraulic pressure caused bythe silicone dielectric compound. If the connector lockingtabs weaken or break off, DO NOT replace the associatedcomponent. Bind the connectors together with tape or aharness tie strap to assure good electrical connection.Ignition CoilThe ignition coil is mounted to the engine block next to thedistributor. Coil operation is dictated by the ignition modulewhich is controlled by the MCU maintaining the terminalsand connectors.When an ignition coil is suspected of malfunctioning, test iton the vehicle. A coil may “break down” after the enginehas heated it to a high temperature. It is important that thecoil be at operating temperature when tested. Perform thetest according to the test equipment manufacturer’sinstructions.Ignition Coil ConnectorThe ignition coil terminals and connector are of uniquedesign. The connector is removed from the coil by graspingboth sides and pulling away from the coil.When a tachometer is required for engine testing or tuneup,connect it using an alligator jaw type connector.Resistance WireA wire with 1.35 ohms resistance is provided in the ignitionwiring to supply less than full battery voltage to the ignitioncoil after the starter motor solenoid is de-energized. Duringengine starting, the resistance wire is bypassed and fullbattery voltage is applied to the ignition coil. The bypass isaccomplished at the I-terminal on the starter motor solenoid.DistributorThe distributor used with the 4.2L engine is equipped withcentrifugal and vacuum assisted advances. Ignition timing iscontrolled through the engine Micro-Computer Unit (MCU).The distributor consists of three groups of components:pickup coil and trigger wheel, ignition advancemechanisms, cap and rotor. The distributor drive gear isinstalled in the distributor shaft and meshes with a spiral cutgear on the camshaft. The end of the distributor shaft isflattened and fits into a slot in the top of the oil pump andprovides the force to drive the oil pump.Pickup Coil and Trigger WheelThe ignition coil primary circuit is opened and closedelectronically by the ignition module. The distributorpickup coil and trigger wheel provide the input signal forthe MCU.The trigger wheel, which is installed on the distributor shaft,has one tooth for each engine cylinder. The wheel is mountedso that the teeth rotate past the pickup coil one at a time.Thle pickup coil has a magnetic field that is intensified bythe presence of ferrous metal (contains iron-can be pickedup with an ordinary magnet). The pickup coil reacts to thetrigger wheel teeth as they pass. As a trigger wheel toothapproaches and passes the pole piece of the pickup coil, itreduces the reluctance (compared to air) to the magneticfield and increases field strength. Field strength decreasesas the tooth moves away from the pole piece. This increaseand decrease of field strength induces an alternating current(pulse) into the pickup coil, which triggers the MCU, whichin turn signals the ignition module. The control unit opensand closes the coil primary circuit according to the positionof the trigger wheel teeth.There aren’t any contacting surfaces between the triggerwheel and pickup coil assembly. The dwell angle isdetermined electronically by the control unit and is notadjustable. When the ignition coil primary circuit isswitched open, the MCU sends a signal to the ignitionmodule that starts an electronic timer in the ignition modulewhich keeps the coil primary only long enough for theelectromagnetic field within the coil to collapse and thevoltage to discharge. The ignition module thenautomatically closes the coil primary circuit. The period oftime the circuit is closed is referred to as dwell.Carp and RotorThe central tower on the distributor cap is connecteddirectly to the high voltage at the coil. The current flowsthrough the spring-loaded contact on the rotor to the carbonbutton in the cap. The rotor tip aligns with a contact in thecap that corresponds to the cylinder to be ignited just as theignition coil output high voltage is applied to the rotor. Inthis way, each spark plug is “fired’ in turn.A unique feature of the SSI is the silicone applied to therotor blade during the manufacture. Radio interference isgreatly reduced by the presence of a small quantity ofsilicone dielectric compound on the rotor blade. After a fewthousand miles, this compound becomes charred by the highvoltage current flowing through the rotor. This condition isnormal. DO NOT scrape residue from the rotor blade.When installing a replacement rotor, apply a thin coat0.75-3.0 mm (0.03-0.12”) of silicone dielectric compoundto the tip of the rotor blade.