The Chrysler Corporation Lean Burn System, introduced in 1976 on the Cordoba, has been made available on a number of Aspen/Volare- models for 1978. This system is based on the principle that lower NO x emissions would occur if the air/fuel ratio inside the cylinder area was raised from its current point (15.5:1) to a much leaner point (18:1).
In order to make the engine workable, a solution to the problems of carburetion and timing had to be found since a lean running engine is not the most efficient in terms of driveability. Chrysler adapted a conventional carburetor to handle the added air coming in, but the real advance of the system is the Spark Control Computer mounted on the air cleaner.
Since a lean burning engine demands precise ignition timing, additional spark control was needed for the distributor. The computer supplies this control by providing an infinitely variable advance curve. Input data is fed instantaneously to the computer by a series of seven sensors located in the engine compartment which monitor timing, water temperature, air temperature, throttle position, idle/off-idle operation, and intake manifold vacuum. The program schedule module of the spark control computer receives the information from the sensors, processes it, and then directs the ignition control module to advance or retard the timing as necessary. This whole process is going on continuously as the engine is running, taking only a thousandth of a second to complete a circuit from sensor to distributor.
The components of the system are as follows: Modified carburetor; Spark Control Computer, consistent of two interacting modules: the Program Schedule Module which is responsible for translating input data, and the Ignition Control Module which transmits data to the distributor to advance or retard the timing; and the following sensors.
Start Pick-up Sensor, located inside the distributor, supplies a signal to the computer providing a fixed timing point which is only used for starting the car. It also has a back-up function of taking over engine timing in case the run pick-up fails. Since the timing in this pick-up is fixed at one point, the engine will be able to run, but not very well.
The Run Pick-up Sensor, also located in the distributor, provides timing data to the computer once the engine is running. It also monitors engine speed and helps the computer decide when the piston is reaching the top of its compression stroke.
Coolant Temperature Sensor, located on the water pump housing, informs the computer when the coolant temperature is below 150°.
Air Temperature Sensor, inside the computer itself, monitors the temperature of the air coming into the air cleaner.
Throttle Position Transducer, located on the carburetor, monitors the position and rate of change of the throttle plates. When the throttle plates start to open and as they continue to open toward full throttle, more and more spark advance is called for by the computer. If the throttle plates are opened quickly even more spark advance is given for about one second. The amount of maximum advance is determined by the temperature of the air coming into the air cleaner. Less advance under acceleration will be given if the air entering the air cleaner is hot, while more advance will be given if the air is cold.
Carburetor Switch Sensor, located on the end of the idle stop solenoid, tells the computer if the engine is at idle or off-idle.
Vacuum Transducer, located on the computer, monitors the amount of intake manifold vacuum present; the more vacuum, the more spark advance to the distributor. In order to obtain this spark advance in the distributor, the carburetor switch sensor has to remain open for a specified amount of time during which the advance will slowly build up to the amount indicated as necessary by the vacuum transducer. If the carburetor switch should close during that time, the advance to the distributor will be cancelled. From here the computer will start with an advance count-down. If the carburetor switch is reopened within a certain amount of time, the advance will continue from a point where the computer decides it should. If the switch is reopened after the computer has counted down to "no advance," the vacuum advance process must start over again.
When you turn the ignition key on, the start pick-up sends its signal to the computer which relays back information for more spark advance during cranking. As soon as the engine starts, the run pick-up takes over and receives more advance for about one minute. This advance is slowly eliminated during the one minute warm-up period. While the engine is cold (coolant temperature below 150° as monitored by the coolant temperature sensor), no more advance will be given to the distributor until the engine reaches normal operating temperature, at which time normal operation of the system will begin.
In normal operation, the basic timing information is relayed by the run pick-up to the computer along with input signals from all the other sensors. From this data the computer determines the maximum allowable advance or retard to be sent to the distributor for any situation.
If either the run pick-up or the computer should fail, the back-up system of the start pick-up takes over. This supplies a fixed timing signal to the distributor which allows the car to be driven until it can be repaired. In this mode, very poor fuel economy and performance will be experienced. If the start pick-up or the ignition control module section of the computer should fail, the engine will not start or run.
TESTING & SERVICE
Some of the procedures in this section refer to an adjustable timing light. This is also known as a spark advance tester, i.e., a device which will measure how much spark advance is present going from one point, a base figure, to another. Since precise timing is very important to the Lean Burn System, do not attempt to perform any engine tests calling for an adjustable timing light without the one. In places where a regular timing light can be used, it will be noted in the text.Troubleshooting
- Remove the coil wire and hold it about 1 / 4 in. away from an engine ground, then have someone crank the engine while you check for spark.
- If you have a good spark, slowly move the coil wire away from the engine and check for arcing at the coil while cranking.
- If you have good spark and it is not arcing at the coil, check the rest of the parts of the ignition system, if they are alright, the problem is not in the ignition system. Check for trouble-shooting the system.
- Check the battery specific gravity; it must be at least 1.220 to deliver the necessary voltage to fire the plugs.
- Remove the terminal connector from the coolant switch and put a piece of paper or plastic between the curb idle adjusting screw and the carburetor switch. This is unnecessary if the screw and switch are not touching.
- Connect the negative lead of a voltmeter to a good engine ground, turn the ignition switch to the RUN position and measure the voltage at the carburetor switch terminal. If you receive a reading of more than five volts, go on to Step 7; if not, proceed to the next step.
- Turn the ignition switch OFF and disconnect the double terminal connector from the bottom of the Spark Control Computer. Turn the ignition switch back to the RUN position and measure the voltage at terminal No. 2; if the voltage is not within 1 volt of the voltage you received in Step 3, check the wiring between terminal No. 2 and the ignition switch. If the voltage is correct, go on to the next step.
- Turn the ignition switch OFF and disconnect the single connector from the bottom of the Spark Control Computer. Using an ohmmeter, check for continuity between terminal No. 7 and the carburetor switch terminal. There should be continuity present, if not, check the wiring.
- Check for continuity between terminal No. 10 (double connector) and ground. If there is continuity, replace the Spark Control Computer; if not, check the wiring. If the engine still will not start, proceed to the next step.
- Turn the ignition switch to the RUN position and check for voltage at terminal No. 1 and ground of the double connector. If you received voltage within 1 volt of that recorded in Step 3, proceed to the next step. If you do not get the correct voltage, check the wiring between the connector and the ignition switch.
- Turn the ignition switch OFF and with an ohmmeter, measure resistance between terminals Nos. 5 and 9 of the dual connector. If you do not receive a reading of 150-900 ohms, disconnect the start pick-up leads at the distributor and measure the resistance going into the distributor. If you get a reading of 150-900 ohms here, the wiring between terminals Nos. 5 and 9 and the distributor is faulty. If you still do not get a reading between 150-900 ohms, replace the start pick-up. If you received the proper reading when you initially checked terminals Nos. 5 and 9, proceed to the next step.
- Connect one lead of an ohmmeter to a good engine ground and with the other lead, check the continuity of both start pick-up leads going into the distributor. If there is not continuity, go on to the next step. If you do get a reading, replace the start pick-up.
- Remove the distributor cap and check the air gap of the start pick-up coil. Adjust, if necessary, and proceed to the next step.
- Replace the distributor cap, and start the engine; if it still will not start, replace the Spark Control Computer. If the engine still does not work, put the old one back and retrace your steps, paying close attention to any wiring which may be shorted.
- Start the engine and let it run for a couple of minutes. Disconnect the start pick-up lead. If the engine still runs, leave this test and go on to the "Start Timer Advance" test. If the engine died, proceed to Step 2.
- Disconnect the run pick-up coil from the distributor. Use an ohmmeter to check for continuity at each of the leads going into the distributor. If there is continuity shown, replace the pick-up coil and repeat Step 1. If you do not get a reading of continuity, proceed to the next step.
- Remove the distributor cap, check the gap of the run pick-up and adjust it if necessary.
- Reinstall the distributor cap, check the wiring, and try to start the engine. If it does not start, replace the computer and try again. If it still does not start, repeat the test paying close attention to all wiring connections.
- Hook up an adjustable timing light to the engine.
- Have an assistant start the engine, place his foot firmly on the brake, then open and close the throttle, then place the transmission in Drive.
- Locate the timing signal immediately after the transmission is put in Drive. The meter on the timing light should show about 5-9° advance. This advance should slowly decrease to the basic timing signal after about one minute. If it did not increase the 5-9° or return after one minute, replace the spark control computer. If it did operate properly, proceed to the next test.
Before performing this test, the throttle position transducer must be adjusted. The adjustments are as follows:
- The air temperature sensor inside the spark control computer must be cool (below 135°). If the engine is at operating temperature, either turn it off and let it cool down or remove the top of the air cleaner and inject a spray coolant into the computer over the air temperature sensor for about 15 seconds. If Steps 2-5 take longer than 3-4 minutes, recool the sensor.
- Start the engine and wait about 90 seconds, then connect a jumper wire between the carburetor switch terminal and ground.
- Disconnect the electrical connector from the transducer and check the timing, adjusting if necessary. Reconnect the electrical connector to the transducer and recheck the timing.
- If the timing is more than specified on the tune-up decal, loosen the transducer locknut and turn the transducer clockwise until it comes within limits, then turn it an additional 1 / 2 turn clockwise and tighten the locknut.
- If the timing is at the specified limits, loosen the locknut and turn the transducer counterclockwise until the timing just begins to advance. At that point, turn the transducer 1 / 2 turn clockwise and tighten the locknut. After this step you are ready to begin the throttle advance test.
- Turn the ignition switch OFF and disconnect the single connector from the bottom of the spark control computer.
- With an ohmmeter, measure the resistance between terminals Nos. 8 and 9 of the single connector. The measured resistance should be between 60-90 ohms. If it is, go on to the next step, if not, remove the connector from the throttle position transducer and measure the resistance at the transducer terminals. If you now get a reading of 60-90 ohms, check the wiring between the computer terminals and the transducer terminal. If you do not get the 60-90 reading, replace the transducer and proceed to the next step.
- Reconnect the wiring and turn the switch to the RUN position without starting the engine. Hook up a voltmeter, negative lead to an engine ground, and touch the positive lead to one terminal of the transducer while opening and closing the throttle all the way. Do the same thing to the other terminal of the transducer. Both terminals should show a 2 volt change when opening and closing the throttle. If not proceed to the next step.
- Position the throttle linkage on the fast idle cam and ground the carb switch with a jumper wire. Disconnect the wiring connector from the transducer and connect it to a transducer that you know is good.
- Move the core of the transducer all the way in, start the engine, wait about 90 seconds, and then move the core out about an inch.
- Adjust the timing light so that it registers the basic timing signal. The timing light should show the additional amount of advance as given in the "Transducer Advance Specifications" chart in this section. If it is within the specifications, move the core back into the transducer, and the timing should go back to the original position. If the timing did advance and return, go on to the next step. If it did not advance and/or return, replace the spark control computer and try this test over again. If it still fails, replace the transducer.
- Reset the timing light meter, and have an assistant move the transducer core in and out 5-6 times quickly. The timing should advance 7-12° for about a second and then return to the base figure. If it did not, replace the spark control computer. If you did not get the 2 volt change in reading in Step 8, you should now replace the transducer since you have proved that the spark control computer is not causing it to check out faulty.
- Remove the test transducer (from Step 9), and reconnect all wiring.
- Hook up an adjustable timing light.
- Turn the ignition switch to the RUN position, but do not start the engine. Disconnect the idle stop solenoid wire and the wiring connector from the coolant switch. Push the solenoid plunger in all the way, and while holding the throttle linkage open, reconnect the solenoid wire. The solenoid plunger should pop out and when the throttle linkage is released, it should also hold the linkage in place. If it does not, replace the idle stop solenoid.
- Start the engine and let it warm up; make sure that the transmission is in Neutral and the parking brake is on.
- Place a small piece of plastic or paper between the carburetor switch and the curb idle adjusting screw; if the screw is not touching the switch, make sure that the fast idle cam is not on or binding; the linkage is not binding, or the throttle stop screw is not overadjusted. Adjust the timing light for the basic timing figure. The meter of the timing light should show 2-5° advance with a minimum of 16 in. of vacuum at the vacuum transducer (checked with a vacuum gauge). If this advance is not present, replace the spark control computer and try the test again. If the advance is present, let the engine run for about 6-9 minutes, then go on to the next step.
- After the 6-9 minute waiting period, adjust the timing light so that it registers the basic timing figure. The timing light meter should now register 32-35° of advance. If the advance is not shown, replace the spark control computer and repeat the test; if it is shown, proceed to Step 6.
- Remove the insulator (paper or plastic) which was installed in Step 4; the timing should return to its base setting. If it does not, make sure that the curb idle adjusting screw is not touching the carburetor switch. If that is alright, turn the engine off and check the wire between terminal No. 7 of the single connector (from the bottom of the spark control computer), and the carburetor switch terminal for a bad connection. If it turns out alright, and the timing still will not return to its base setting, replace the spark control computer.
- Connect one lead of the ohmmeter to a good engine ground, the other to the black wire with a tracer in it. Disregard the orange wire if there is one on the switch.
- If the engine is cold (below 150°), there should be continuity present in the switch. With the thermostat open, and the engine warmed up, there should be no continuity. If either of the conditions in this step are not met, replace the switch.
This procedure is to set the basic timing signal as shown on the engine tune-up decal in the engine compartment.
- Connect a jumper wire between the carburetor switch terminal and the ground. Connect a standard timing light to the No. 1 cylinder.
- Block the wheels and set the parking brake. If the car has an automatic release type parking brake, remove and plug the vacuum line which controls it from the fitting on the rear of the engine.
- Start and warm the engine up; raise engine speed above 1,500 rpm for a second, then drop the speed and let it idle for a minute or two.
- With the engine idling at the point specified on the tune-up decal with the transmission in Drive, adjust the timing to the figure given on the tune-up decal.
- Follow the first three steps under "Lean Burn Timing," then insert an exhaust gas analyzer into the tailpipe.
- Place the transmission in Drive, the air conditioning and headlights off. Adjust the idle speed to the specification shown on the tune-up decal by turning the idle solenoid speed screw.
- Adjust the carbon monoxide level to 0.1% with the mixture screws while trying to keep hydrocarbons to a minimum and the idle speed to specification. Turn the screws alternately over their range to coordinate all three factors.
- Place the transmission in Neutral; disconnect the wire at the idle stop solenoid and adjust the curb idle speed screw to obtain 650 rpm. Reconnect the wire.
- Remove the air cleaner cover and lift and support the air cleaner assembly high enough to gain access to the fast idle adjustment screw.
- Place the fast idle speed screw on the highest step of the cam and adjust the idle speed to the specification shown on the tune-up decal.
- Drop the idle back down to the curb idle position and turn the ignition switch off. Reconnect any hoses or electrical connections taken off in the procedure.
- If the procedure has to be performed a second time, make sure that you start from the beginning or the readings will be inaccurate.
REMOVAL & INSTALLATION
None of the components of the Lean Burn System (except the carburetor), are able to be disassembled and repaired. When one part is known to be defective, it is replaced.
The Spark Control Computer is secured by mounting screws inside the air cleaner. To remove the Throttle Position Transducer, loosen the locknut and unscrew it from the mounting bracket, then unsnap the core from the carburetor linkage.