Ignition System Chrysler Fifth Avenue II

DESCRIPTION

The Electronic Spark Control (ESC) system consists of a Spark Control Computer, various engine sensors, a specially-calibrated carburetor and a dual pick-up distributor. The ESC system is designed to burn a lean air/fuel mixture with a minimum of emissions.

SPARK CONTROL COMPUTER

The Spark Control Computer (SCC) is located on the air cleaner assembly. It gives the system the capability of igniting a lean air/fuel mixture according to different modes of engine operation by delivering an infinitely variable advance curve. The computer determines optimum ignition advance.

The SCC signals the ignition coil to produce the voltage required for ignition purposes. The voltage produced is based on the demands of air/fuel ratio, air and coolant temperature, load and RPM. The computer consists of one electronic printed circuit board which receives signals from all the sensors and computes the appropriate ignition advance. Computer reaction time is measured in milliseconds.

SENSORS

The electronic spark control computer, mounted on the air cleaner, uses up to 7 engine sensors to determine when to fire the spark plugs. (Scheme 1) These include the distributor pick-up coils, vacuum transducer, coolant temperature sensor, carburetor switch, detonation sensor, oxygen sensor, and charge temperature switch (if equipped).

Electronic Spark Control Sensor Locations. Scheme 1

Magnetic Pick-Up Assembly

The pick-up coil assembly is located in the distributor. The start pick-up coil supplies a signal to the computer, which causes the spark plugs to fire at a fixed amount of advance during cranking only. Once the engine begins to run, the run pick-up coil takes over, supplying advance information to the computer.

The computer then modifies spark advance based on information from remaining sensors. The start pick-up coil can be identified by its 2-prong male connector. The run pick-up coil can be identified by its connector having one male prong and one female prong.

Coolant Sensor

On 2-Bbl.federal models the coolant sensor is mounted in the charge temperature area of the intake manifold. It is located in the intake manifold on all other models. The coolant sensor informs the computer of the engine temperature. This prevents the changing of the air/fuel ratio until the engine reaches normal operating temperature. It also controls the amount of spark advance when engine is cold.

Vacuum Transducer

The vacuum transducer, located on the spark control computer, signals the computer to inform it of engine operating vacuum. Vacuum is one of the factors used to determine whether the computer will advance or retard ignition timing or change the air/fuel ratio.

Carburetor Switch

The carburetor switch (if equipped) is located on the carburetor and signals the computer when engine is at idle. The computer cancels spark advance at idle, and controls idle air/fuel ratio.

Detonation Sensor

The detonation sensor is located in the No. 2 intake manifold port. It senses detonation or "knocking". The computer will retards ignition timing a maximum of 20° when detonation is detected by the sensor. Timing is returned to its original advance when detonation is no longer detected.

Oxygen Sensor

The oxygen sensor is located in the exhaust manifold. It informs the computer the amount of oxygen in the exhaust gases. The computer then adjusts the air/fuel ratio to maintain maximum operating efficiency.

Charge Temperature Switch

The charge temperature switch is located in the No. 8 intake port, on the intake manifold. When intake airflow temperature is less than 60°F (15°C), the charge temperature switch is closed. This prevents the EGR timer and the EGR valve from operating. It also switches the air injection to upstream into the exhaust manifold.

Distance Sensor

The distance sensor is located in series with the speedometer cable and transmission. This sensor is a reed switch type sensor. It produces a specific number of switch closures per input shaft rotation. The number of switch closures is calculated by the SCC to determine vehicle speed.

SYSTEM OPERATION

The 2 functional modes of the Spark Control Computer are "Start" and "Run". The "Start" mode operates while cranking and starting only. The "Run" mode operates after the engine has started and during normal engine operation. The 2 modes never operate at the same time.

During cranking and starting the pick-up coil sends a signal to the computer which is in the "Start" mode. The "Run" mode is by-passed. During this time a fixed ignition advance is used. Advance is determined by distributor position (base timing).

The pick-up coil continues to send a signal to the computer after the engine starts. The computer is now in the "Run" mode and "Start" mode is by-passed. The amount of timing advance in the "Run" mode is controlled by the computer, based upon information received from the engine sensors.

Engine RPM and vacuum are the 2 factors determining ignition advance. When the ignition event occurs, depends upon computer programming. Advance from vacuum will be provided when the carburetor switch is open. The amount of advance is programmed into the computer and is proportional to the amount of vacuum and engine RPM.

Advance from an increase in RPM will be given by the computer when the carburetor switch is open and the computer is programmed to engine RPM. If there is a failure of the "Run" mode of the computer, the "Limp-In" mode will come into service and allow the vehicle to be driven in for repair. Performance and economy will be greatly reduced because of fixed and therefore retarded timing. If the "Start" mode or both pick-up coils fail, the vehicle will not start or run.

PICK-UP COIL AIR GAP

Align one reluctor tooth with start pick-up coil. Loosen pick-up coil hold-down screw. Insert a.006" (.15 mm) non-magnetic feeler gauge between reluctor tooth and start pick-up coil. Adjust air gap so that contact is made between reluctor tooth, feeler gauge, and pick-up coil. Tighten hold down-screw. (Scheme 2)

Checking Distributor Pick-Up Coil Air Gap. Scheme 2

1. Remove feeler gauge. No force should be required to remove feeler gauge. Check air gap with a .008" (.20 mm) feeler gauge. The .008" (.20 mm) feeler gauge should not fit into gap. DO NOT force feeler gauge into gap. If .008" (.20 mm) feeler gauge does fit into gap, repeat adjustment procedure.
2. The run pick-up coil air gap can be adjusted using the same procedure as for the start pick-up coil. Adjust the run pick-up coil air gap using a .012" (.30 mm) non-magnetic feeler gauge and check gap with a .014" (.35 mm) feeler gauge. The .014" (.35 mm) feeler gauge should not fit into gap.

COMPUTER CONTROLLED SPARK ADVANCE TEST

1. Warm vehicle engine to normal operating temperature. Place a thin piece of insulating material between curb idle adjusting screw and carb switch (ensure no contact is being made).
2. Remove and plug vacuum line at vacuum transducer. Connect auxiliary vacuum supply to vacuum transducer and set vacuum at 16 in. Hg. Increase engine speed to 2000 RPM, wait one minute and compare timing advance against specifications. If correct advance cannot be obtained, replace SCC computer.

CARBURETOR SWITCH TEST

Note. Grounding the carburetor switch eliminates all spark advance on most systems.

1. With key off, disconnect 10-way connector from SCC computer. With throttle completely closed, check for continuity between pin No. 7 and ground. If no continuity is present, check wire and carburetor switch for an open or short. Recheck basic timing.
2. With throttle open, check for continuity between pin No. 7 and ground. There should be no continuity.

CHARGE TEMPERATURE SENSOR

With key off, disconnect wire connector from charge temperature sensor. Connect ohmmeter between terminals of charge temperature sensor. Temperature sensor should have approximately 2500 ohms at room temperature (70°F) and more than 6000 ohms at normal operating temperature (200°F).

1. Connect an adjustable timing light or magnetic timing light to the engine. Start engine and run it to at least 1200 RPM. Connect an auxiliary vacuum supply to vacuum transducer and apply 16 in. Hg. Tap lightly on intake manifold near detonation sensor with a small metal object.
2. Using a timing light look for a decrease in spark advance. The decrease in timing should directly respond to the strength of the tapping. The maximum decrease in timing is 20 degrees. Shut off engine and disconnect timing light.

ELECTRONIC EXHAUST GAS RECIRCULATION

Note. The engine temperature sensors must be working properly before performing this test.

1. With engine cold and ignition switch in the "OFF" position, connect a voltmeter between Gray wire of EGR solenoid and ground. Start engine. The voltmeter should read less than one volt.
2. It should remain at less than one volt until engine reaches normal operating temperature and the electronic EGR schedule has timed out. The solenoid should then de-energize and voltmeter should read charging system voltage. If not, replace solenoid and repeat this step. NOTE: Federal 318 CID, 2-barrel engines have no thermal delay below 60°F (15°C). They will follow the EGR time delay schedule only.
3. If the voltmeter reads charging system voltage before EGR timer has timed out, replace computer or the externally mounted EGR timer. If the engine is started hot, the EGR solenoid will only be energized for the length of the time delay schedule, it will then de-energize.

ELECTRONIC THROTTLE CONTROL SYSTEM

Note. The spark control system is integral with the electronic throttle system. A solenoid mounted on the carburetor is energized whenever the A/C compressor, Electronic Backlite (EBL) or electronic timers are activated. The electronic timers used in the ignition system operate when the throttle is closed (plus a time delay of 2 seconds) or after an engine start condition.

1. Connect a tachometer to engine. Start engine and run until normal operating temperature is reached. Depress accelerator and let up. A higher than curb idle speed should be seen for the length of the EGR timer.
2. On vehicles equipped with A/C, turn on A/C and EBL. Depress accelerator pedal momentarily. This should cause a higher than normal curb idle speed. Turning the A/C and EBL off, should cause a normal curb idle speed.
3. If speed increases do not occur, disconnect 3-way connector at carburetor. Check the solenoid with an ohmmeter by measuring the resistance from Black wire terminal to ground. If resistance is not between 15-35 ohms, replace the solenoid.
4. Start vehicle and measure the voltage of the Black wire of 3-way connector before the delay times out. The voltmeter should read charging voltage. If not, replace SCC computer.
5. Turning on the A/C or EBL should also produce a charging system voltage on the Black wire of the 3-way connector after the delay has timed out. If not, check the wiring to the instrument panel for an open.

SYSTEM STARTING TEST

1. Turn ignition on. Disconnect coil wire from distributor cap. Hold end of coil wire approximately 1.4" (6 mm) away from a good engine ground. Intermittently ground coil negative terminal, using a jumper wire. Look for a good bright Blue spark.
2. If spark is acceptable, intermittently ground negative coil terminal while slowly moving coil wire away from ground. Look for arcing at the coil tower. If arcing occurs, replace coil. If spark is weak or no spark is produced, perform failure to start test. See FAILURE TO START test in this article. If spark is acceptable and there is no arcing at coil, check ignition system secondary circuit.

Scheme 3

1. If system fails to start, perform SYSTEM STARTING TEST. If there is spark, go to step 4). If there was no spark, turn ignition off. Disconnect 10-way connector from spark control computer. Turn ignition on. Hold coil wire approximately 1/4" from engine ground. Using a jumper wire, intermittently ground negative coil terminal.
2. If there is spark, replace spark control computer. If there is no spark, check voltage at coil positive terminal, using a voltmeter. Voltage should be within 1 volt of battery voltage. If voltage is correct, go to step 3). If voltage is incorrect, check for continuity between coil positive terminal and ignition switch. If there is no continuity, repair wire.
3. Using a voltmeter, check voltage at coil negative terminal. Voltage should be within one volt of battery voltage. If voltage is incorrect, replace coil. If voltage is correct, but there is no spark when grounding coil negative terminal, replace coil.
4. Turn ignition switch to "RUN" position. Use a voltmeter to check voltage at terminal No. 1 of disconnected 10-way connector. (Scheme 3) Check wire between coil negative terminal and terminal No. 1 of 10-way connector. Voltage must be within one volt of battery voltage. (Scheme 3): 10-Way Connector Testing Terminals
5. If voltage is within 1 volt of battery voltage, place a piece of paper between carb idle adjusting screw and carburetor switch. With ignition switch in "RUN" position, check voltage at carburetor switch connector, using a voltmeter. If voltage is not within 1 volt of battery voltage, turn ignition off.
6. Disconnect 10-way connector. Turn ignition switch to "RUN" position. Check voltage at terminal No. 2 of 10-way connector, using a voltmeter. If voltage is not within 1 volt of battery voltage, check wiring between terminal No. 2 of 10-way connector and ignition switch.
7. If voltage is within 1 volt of battery voltage, check for continuity between terminal No. 7 and carburetor switch terminal, using an ohmmeter. If there is no continuity, check wiring between carburetor switch and terminal No. 7. If there is continuity, check for continuity between terminal No. 10 and engine ground.
8. If there is continuity, replace spark control computer. If there is no continuity, check wiring between terminal No. 10 and engine ground. If engine still fails to start, turn ignition off. Check resistance between terminals No. 5 and 9, and No. 3 and No. 9, using an ohmmeter. Resistance should be 150-900 ohms.
9. If resistance is okay, go to step 10). If resistance is not okay, disconnect pick-up leads and check resistance between start pick-up leads. Resistance should be 150-900 ohms. Check resistance between run pick-up leads. Resistance should be 150-900 ohms. If resistance is okay, repair wiring from pick-up to 10-way connector. If resistance is not okay, replace bad pick-up.
10. Check for continuity between each pick-up coil lead and ground. If there is continuity, replace bad pick-up. If there is no continuity, reconnect pick-up leads and check air gap. Reconnect all connections and start vehicle. If vehicle fails to start, replace spark control computer.

IGNITION COIL RESISTANCE

1. Turn ignition off. Disconnect ignition coil wiring. Connect ohmmeter leads to positive and negative ignition coil primary terminals. Primary resistance should read 1.34-1.55 ohms for Prestolite, Echlin, and Essex coils.
2. Connect ohmmeter leads to ignition coil negative terminal and ignition coil tower. Secondary resistance should be 9400-11,700 ohms for Prestolite coils and 9000-12,200 ohms for Echlin and Essex coils. If ignition coil is not to specification, replace coil.

DISASSEMBLY

1. Remove distributor cap. Using 2 screwdrivers, pry off rotor from shaft. Remove reluctor by prying up from bottom of reluctor using 2 pry bars or screwdrivers with a maximum width of 7/16". Be careful not to distort or damage reluctor teeth.
2. Remove 2 screws and lock washers attaching plate to housing. Lift out plate and pick-up coils as an assembly. Do not attempt to remove distributor cap clamps.
3. If distributor has more than .006" (.15 mm) shaft side play, replace housing shaft and reluctor sleeve by removing shaft retaining pin and sliding retainer off end of shaft.
4. Use a file to clean burrs from around pin hole in shaft and remove lower thrust washer. Push shaft up and remove shaft through top of distributor housing.

REASSEMBLY

1. Inspect all bearing surfaces and pivot pins for roughness, binding, or looseness. Lubricate and install upper thrust washer on shaft and slide shaft into distributor housing.
2. Install distributor shaft retainer and pin. Install lower plate, upper plate, and pick-up coils as an assembly.
3. Position reluctor keeper pin into place on reluctor sleeve and firmly press reluctor into place. Make sure keeper pin is in place. Lubricate felt pad in top of reluctor sleeve and install rotor and cap.

Exploded View of V8 ESC Distributor. Scheme 4