Ignition System - Mitsubishi Electronic Dodge Caravan I

DESCRIPTION

The Electronic Ignition System used with the 2.6L engine consists of a battery, ignition switch, ignition coil, IC igniter (electronic control unit), spark plugs and wiring. (Scheme 5) The IC (integrated circuit) igniter is built into distributor.

The distributor consists of a power distributing section, a signal generator (reluctor and pick-up coil assembly), an IC igniter, centrifugal and vacuum advance mechanisms and drive gear.

Scheme 5

OPERATION

As the distributor shaft turns, a reluctor rotates inside the pick-up coil assembly. As reluctor teeth pass the pick-up coil, a signal is generated similar to that produced by a small magneto generator. The signal is produced in synchronization with distributor shaft rotation, 4 times per rotation and at equally spaced intervals.

The signal generated is sent to the IC igniter. The igniter switches current on or off in the ignition coil primary circuit. As current is shut off, the magnetic field in the coil primary circuit collapses. This results in a voltage surge in the secondary circuit, firing the appropriate spark plug.

The centrifugal advance mechanism is located under the rotor. As engine speed increases, the weights move outward, causing the reluctor to rotate ahead of the distributor shaft, advancing timing.

The vacuum advance has a spring-loaded diaphragm connected to the breaker assembly. As engine vacuum increases, the diaphragm pivots the movable breaker assembly in a direction opposite to shaft rotation, advancing ignition timing.

ADJUSTMENTS

The only adjustments that can be made to this system are basic ignition timing (distributor position) and spark plug gap.

Scheme 6

1. Remove secondary wire from distributor center tower. Hold end of wire about 3/8" from a good engine ground. Crank engine and check for spark. (Scheme 6) (Scheme 6): Testing Ignition System for Spark Hold end of wire approximately 3/8" from ground. Courtesy of Chrysler Motors.
2. If no spark is present, proceed to step 4). If spark is present, slowly move secondary wire away from ground, while continuing to crank engine. Check for arcing at coil tower. If arcing occurs at coil tower, replace ignition coil.
3. If spark was okay and there was no arcing at coil tower, secondary voltage is adequate. Inspect distributor rotor, cap, ignition wires and spark plugs. If all components are okay, inspect fuel system. Ensure that no mechanical damage has occurred to engine components.
4. If in step 2) spark was weak, inconsistent, or there was no spark, turn ignition on. Connect positive voltmeter lead to negative terminal of ignition coil. Connect negative lead to a good ground. Voltage reading should be battery voltage.
5. If battery voltage is present, proceed to step 6). If reading is 3 volts or less, IC igniter is defective. If there is no voltage, check for open circuit in ignition coil or wiring harness.
6. If battery voltage is indicated in step 4), hold coil secondary wire about 1/4" from a good ground. Using a special jumper wire, momentarily touch ignition coil negative terminal to ground. (Scheme 7) A spark should result.
7. If adequate spark is present, but engine will not start, proceed to step 9). If no spark is present, check for voltage at positive terminal of ignition coil with ignition on (voltmeter positive lead to positive terminal, negative lead to ground).
8. Reading should be at least 12 volts. If voltage is as specified, ignition coil is defective and must be replaced. If voltage is not to specification, check wiring and connections.
9. If in step 6) a spark was produced, but vehicle will not start, replace IC igniter.

IC IGNITER

1. To check IC igniter, connect one lead of 12-volt test light to output side of IC igniter. Attach battery positive terminal to IC igniter battery terminal and negative terminal to IC igniter base. Other test light lead should be attached to positive battery wire. (Scheme 8)
2. Using a dry battery or ohmmeter, apply voltage to signal input terminals of IC igniter. Test light should illuminate when signal voltage is applied and go out when it is removed. If not, replace IC igniter.
3. If light does not operate as stated, IC igniter is defective. If light does operate properly, IC igniter still could be faulty. Part substitution is recommended as a final test in such cases.

Scheme 7

Testing IC Igniter Operation Polarity of ohmmeter or dry battery may be reversed. Courtesy of Chrysler Motors. Scheme 8

PICK-UP COIL RESISTANCE

Turn ignition off. Connect ohmmeter to pick-up coil. (Scheme 9) Resistance should be 920-1120 ohms. If resistance is not to specification, replace pick-up coil assembly.

Scheme 9

IGNITION COIL RESISTANCE

1. Connect ohmmeter leads to positive and negative terminals of ignition coil. Ignition should be off and wire should be removed from positive terminal of ignition coil to isolate it from system. Primary resistance should be .70-.85 ohm.
2. With ignition off, connect ohmmeter leads to coil negative terminal and coil tower terminal. Secondary resistance should read 9000-11,000 ohms. If either reading exceeds specifications, replace ignition coil.

SECONDARY WIRE RESISTANCE

To check coil-to-distributor wire and spark plug wire resistance, connect ohmmeter leads to each end of wire. Resistance should be less than 22,000 ohms per wire. If specification is exceeded, replace ignition wires.

CENTRIFUGAL ADVANCE MECHANISM

Run engine at idle speed. Remove vacuum hose (non-striped) from vacuum controller. Slowly increase engine speed and check for advance. If advance is excessive, check for deteriorated governor spring. A broken spring will result in abrupt advance. If advance is insufficient, check governor weights and cam for faulty operation.

VACUUM ADVANCE MECHANISM

1. Set engine speed at 2500 RPM. Check for advance by disconnecting and connecting distributor vacuum hose. If available, connect a vacuum pump after removing distributor vacuum hose. Run engine at idle and slowly apply vacuum to check for advance.
2. If advance is excessive, check for deteriorated or sagging vacuum controller. If advance is insufficient or there is no advance, breaker plate is not operating properly or vacuum diaphragm is damaged.

REMOVAL

Disconnect negative battery cable. Mark distributor position for reassembly reference. Disconnect wiring harness from distributor. Remove distributor cap and plug wires. Remove rotor. Disconnect vacuum advance hose from distributor. Remove distributor mounting nut and distributor assembly.

Scheme 10

1. Remove centrifugal advance components as an assembly by removing bolt in top of shaft. Due to extreme tension on bolt, a socket or box wrench should be used for this purpose.
2. If governor assembly is further disassembled, ensure 2 different springs are properly identified for correct reassembly. Remove wire clamp screw. Remove clamp. Remove 2 pick-up coil and IC igniter mounting screws. Remove pick-up coil and IC igniter as an assembly.
3. Remove 2 vacuum advance diaphragm mounting screws. Disengage vacuum diaphragm from breaker assembly. Remove 2 screws retaining breaker assembly. Lift assembly from distributor housing. Place breaker assembly on clean shop towel.
4. Remove 2 screws from bearing retainer plate. Lift out plate. Mark location of drive gear on distributor shaft for reassembly reference. Drive out roll pin. Remove drive gear. Lift distributor shaft and bearing assembly from housing. Remove housing seal.

REASSEMBLY

To reassemble, reverse disassembly procedure. Inspect distributor cap for cracks, flashover, damage to carbon brush and worn terminals. Remove light scaling from terminals. Ensure grease on back side of IC igniter is not removed, it is necessary for heat dissipation. Apply grease to all sliding surfaces.

INSTALLATION

To install, reverse removal procedure.