Except Premier and Monaco
See Figures 1 through 5
All vehicles equipped with a 3.0L engine, except for Premier and Monaco, have a 60° V6 engine. The ignition system on these 3.0L engines is regulated by the Powertrain Control Module (PCM), also named the Single Board Engine Controller (SBEC) on the TC by Maserati vehicles. The PCM supplies battery voltage to the ignition coil through the Auto Shutdown (ASD) relay. The PCM also controls the ground circuit for the ignition coil. By switching the ground path for the coil on and off, the PCM adjusts the ignition timing to meet changing engine operating conditions.
During the crank-start period, the PCM advances ignition timing a set amount. During engine operation, the amount of spark advance provided by the PCM is determined by these input factors:
The PCM also regulates the fuel injection system. Refer to Driveability & Emissions Controls for electronic engine controls and components.
The distributor pick-up provides two inputs to the PCM. From one input the PCM determines the engine speed (RPM). From the other input it derives the crankshaft position. The PCM regulates injector synchronization and adjusts the ignition timing and engine speed based on these inputs.
The distributor pick-up contains two signal generators. The pick-up unit consists of 2 light emitting diodes (LEDs), 2 photo diodes, and a separate timing disk. The timing disk contains two sets of slots. Each set of slots rotates between a light emitting diodes and photo diodes. The inner set contains 6 large slots, one for each cylinder. The outer set contains several smaller slots.
The outer set of slots on the rotating disk represents 2 degrees of crankshaft rotation. Up to 1,200 RPM, the PCM uses the input from the outer set of slots to increase ignition timing accuracy.
The outer set of slots contains a 10° flat spot. This area is not slotted. The flat spot tells the PCM that the next piston at Top Dead Center (TDC) will be number 6. Each piston's position is referenced by one of the six inner slots.
As each slot on the timing disk passes between the diodes, they interrupt the beam from the LED. This creates an alternating voltage in each photo diode which is converted into on-off pulses. The pulses are then input to the PCM.
During cranking, the PCM cannot determine which cylinder will be at TDC until the 10° flat spot on the outer set of slots rotates through the optical unit. Once the flat spot is detected, the PCM knows that piston number 6 will be the next piston at TDC.
Since the disk rotates at half crankshaft speed, it may take up to 2 engine revolutions during cranking before the PCM can determine the position of piston number 6.AUTO SHUTDOWN (ASD) RELAY
The PCM operates the Auto Shutdown (ASD) relay and fuel pump relay through one ground path. The PCM operates the relays by switching the ground path on and off. Both relays turn on and off at the same time.
The ASD relay connects the battery voltage to the fuel injector and ignition coil. The fuel pump relay connects the battery voltage to the fuel pump and oxygen sensor heating element.
The PCM turns the ground path off when the ignition switch is in the OFF position. Both relays are off. When the ignition switch is in the ON or crank position, the PCM monitors the distributor pick-up signal. From the pick-up signal, the PCM determines engine speed and ignition timing (coil dwell). If the PCM does not receive a distributor signal when the ignition switch is in the RUN position, it will de-energize both relays. When the relays are de-energized, battery voltage is not supplied to the fuel injector, ignition coil, fuel pump and oxygen sensor heating element.
On New Yorker, Dynasty, Daytona, LeBaron coupe or convertible, Imperial and Fifth Ave. models, the ASD relay and fuel pump relay are located in the Power Distribution Center. On LeBaron sedan, Spirit, Acclaim, Shadow and Sundance models, the ASD relay and fuel pump relay are mounted on the driver's side fender well, next to the strut tower.IGNITION COIL
The 3.0L engines use an epoxy type coil, which is not oil filled. The windings are embedded in a heat and vibration resistant epoxy compound.
The PCM operates the ignition coil through the ASD relay. When the relay is energized by the PCM, battery voltage is connected to the ignition coil positive terminal. The PCM will de-energize the ASD relay if it does not receive an input from the distributor pick-up. The coil is mounted on the rear of the intake manifold next to the air cleaner.Premier and Monaco
The 1991-92 Dodge Monaco and the Eagle Premier were equipped with either an electronic distributor ignition system or an electronic distributorless ignition system. If your vehicle is equipped with one coil and a distributor cap mounted on the front of the left-side (radiator side) engine cylinder head, it has the electronic distributor ignition system. For the distributorless system, refer to procedures described later in this section.CONVENTIONAL IGNITION SYSTEM
See Figures 6 through 10
The ignition system used on the Premier and Monaco's 3.0L engine with an electronic distributor ignition system consists of:
Ignition Control Module (ICM)
The Ignition Control Module (ICM) is mounted to the ignition coil. Based on control system inputs, the ECU triggers the ignition coil via the ICM. The ECU is able to advance or retard ignition timing by controlling the ignition coil through the ICM.
The ICM consists of a solid-state ignition circuit, an integrated ignition circuit and an integrated ignition coil that can be removed and serviced separately, if necessary.
The ECU provides an input signal to the ICM. The ICM has only two outputs:
The electrical feed to the ICM is through terminal A of connector No. 1 on the module. Electrical supply only occurs with the ignition switch in the START and RUN position. Terminal B of connector No. 1 is grounded at the engine oil dipstick bracket along with the ECU ground wire and oxygen (O 2 ) sensor ground.
The tachometer output signal wire of the ICM is connected to Pin No. 1 of the D1 diagnostic connector. The wire is routed to the diagnostic connector through a short section of the ECU harness, the engine and instrument panel harness. This type of routing eliminates any potential electrical interference in the various ECU circuitry.
Ignition firing signals from the ECU terminal 27 are transmitted through terminal B of connector No. 2 on the ICM. The ignition signal from the ECU is received by the ICM in the form of a 5 volt square wave. As the leading edge of the wave contacts the ignition circuitry in the ICM, the ICM charges the coil primary windings.
When coil saturation occurs, the module circuitry opens the primary windings to collapse the magnetic field in the windings. This induces the high voltage in the coil secondary windings, which is then transmitted to the spark plugs via the coil wire, distributor cap and rotor.ECU Inputs
The ECU receives input from four primary sources:
The speed sensor, attached to the torque converter drive plate housing, provides an input signal to the ECU relating to the crankshaft angle (position). The ECU converts the rate of change of crankshaft angle into engine RPM and the crankshaft angle to piston position. The speed sensor determines TDC, degrees Before TDC (BTDC) and engine speed by detecting the flywheel teeth as they pass during engine operation. The speed sensor is non-adjustable.
The drive plate pulse ring has three trigger notches, 120° apart. There are 20 small teeth (windows) between each trigger notch. Each large trigger notch is located 12 small teeth before each TDC position of the corresponding pistons.
When a tooth and notch pass the magnetic core of the speed sensor, a voltage spike is induced in the sensor pick-up coil winding. The voltage spikes allow the ECU to count the teeth as they pass the sensor. When a trigger notch passes the speed sensor, there is a longer than usual delay between voltage spikes. This longer delay tells the ECU that a piston will be at the TDC position 12 voltage spikes later. The ECU uses information from the speed sensor to control spark timing and fuel injection timing for each cylinder. The longer voltage spike indicates to the ECU that a piston will soon be at TDC position, 12 teeth later. The ignition timing for the particular cylinder is either advanced or retarded as necessary by the ECU according to sensor inputs.