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Maverick and Comet Repair

Emission Controls

DUAL DIAPHRAGM DISTRIBUTOR ADVANCE AND RETARD MECHANISMS TEST

  1. Connect a timing light to the engine. Check the ignition timing.
    NOTE: Before proceeding with the tests, disconnect any spark control devices, distributor vacuum valves, etc. If these are left connected, inaccurate results may be obtained.
  2. Remove the retard hose from the distributor and plug it. Increase the engine speed. The timing should advance. If it fails to do so, then the vacuum unit is faulty and must be replaced.
  3. Check the timing with the engine at normal idle speed. Unplug the retard hose and connect it to the vacuum unit. The timing should instantly be retarded from 4-10°. If this does not occur, the retard diaphragm has a leak and the vacuum unit must be replaced.

 

PORTED VACUUM SWITCH (DISTRIBUTOR VACUUM CONTROL VALVE) TEST

  1. Check the routing and connection of all vacuum hoses.
  2. Attach a tachometer to the engine.
  3. Bring the engine up to the normal operating temperature. The engine must not be overheated.
  4. Note the engine rpm, with the transmission in Neutral, and the throttle in the curb idle position.
  5. Disconnect the vacuum hose from the intake manifold at the temperature-sensing valve. Plug or clamp the hose.
  6. Note the idle rpm with the hose disconnected. If there is no change in rpm, the valve is good. If there is a drop of 100 or more
    rpm, the valve should be replaced. Replace the vacuum line.
  7. Check to make sure that the all-season cooling mixture meets specifications, and that the correct radiator cap is in place and functioning.
  8. Block the radiator air flow to induce a higher-than-normal temperature condition.
  9. Continue to operate until the engine temperature or heat indicator shows above normal.

If engine speed by this time has increased 100 or more rpm, the temperature-sensing valve is satisfactory. If not, it should be replaced.

DECELERATION (DISTRIBUTOR VACUUM ADVANCE CONTROL) VALVE TEST

  1. Connect a tachometer to the engine and bring the engine to the normal operating temperature.
  2. Check the idle speed and set to specifications with the headlights on high beam if necessary.
  3. Turn off the headlights and note the idle rpm.
  4. Remove the plastic cover from the valve. Slowly turn the adjusting screw counterclockwise without pressing in. After five, and no more than six, turns, the idle speed should suddenly increase to about 1000 rpm. If the speed does not increase after six turns, push inward on the end of the valve spring retainer and release. Speed should now increase.
  5. Slowly turn the adjusting screw clockwise until the idle speed drops to the speed noted in Step 3. Make one more turn clockwise.
  6. Increase the engine speed to 2000 rpm, hold for five seconds and release the throttle. The engine should return to idle speed within four seconds. If idle is not resumed in four seconds, back off the dashpot adjustments and repeat the check. If the idle is not resumed in three seconds with the dashpot backed off, turn the deceleration valve adjustment screw an additional quarter turn clockwise and repeat the check. Repeat the quarter-turn adjustments and idle return checks until the engine returns to idle within the required time.
  7. If it takes more than one complete turn from Step 5 to meet the idle return time specification, replace the valve.

SPARK DELAY VALVE TEST
NOTE: If the distributor vacuum line contains a cut-off solenoid, it must be open during this test.

  1. Detach the vacuum line from the distributor at the spark delay valve end. Connect a vacuum gauge to the valve, in its place.
  2. Connect a tachometer to the engine. Start the engine and rapidly increase its speed to 2,000 rpm with the transmission in Neutral.
  3. As soon as the engine speed is increased, the vacuum gauge reading should drop to zero.
  4. Hold the engine speed at a steady 2,000 rpm. It should take longer than two seconds for the gauge to register 6 in. Hg. If it takes less than two seconds, the valve is defective and must be replaced.
  5. If it takes longer than the number of seconds specified in the application chart for the gauge to reach 6 in. Hg, disconnect the vacuum gauge from the spark delay valve. Disconnect the hose which runs from the spark delay valve to the carburetor at the valve end. Connect the vacuum gauge to this hose.
  6. Start the engine and increase its speed to 2,000 rpm. The gauge should indicate 10-16 in. Hg. If it does not, there is a blockage in the carburetor vacuum port or else the hose itself is plugged or broken. If the gauge reading is within specification, the valve is defective.
  7. Reconnect all vacuum lines and remove the tachometer, once testing is completed.

DISTRIBUTOR MODULATOR SYSTEM
System Test

  1. By-pass the control module by connecting the carburetor vacuum port and single vacuum hose (upstream of temperature-sensing vacuum control valve) to the distributor together at the rear of the engine.
  2. Check the distributor vacuum advance operation. If it is correct, the difficulty is probably in the modulator system.
  3. Return all connections to normal. Pull the hose from the carburetor vacuum port and connect a vacuum gauge in its place.
    Note the vacuum reading at 1500 rpm. Remove the gauge and replace the hose.
  4. By-pass the control module as in Step 1. Connect the vacuum gauge to the primary (outside) distributor vacuum connection. Note the vacuum reading at 1500 rpm.
  5. Remove the control module by-pass hose. Reconnect the module hoses. If the vacuum reading is zero or less than that in Step 3, check for blockage or leaks in the vacuum system. If the vacuum readings are about equal, proceed with Step 6.
  6. Leave the vacuum gauge connected as in Step 4. With the engine idling at normal operating temperature, raise the rear wheels. Disconnect the thermal switch from the pillar post. Hold it in your hand long enough to warm it above 68°F.
  7. Shift into Drive and slowly accelerate to 35 mph. Note the vacuum reading. If the gauge reads zero at all speeds, check the electrical connections, hose connections, and control module. If the vacuum cuts in between 20-30 mph, the system is operating correctly. If vacuum cuts in at the start of acceleration or before 20 mph, check the electrical connections, hose connections, control module, and speed sensor.

Speed Sensor Test

  1. Unplug the sensor. Using an ohmmeter, attach one lead to each speed sensor wire connection. The reading should be 40-60 ohms at room temperature.
  2. Attach one ohmmeter lead to the black wire on the speed sensor and the other to the sensor housing. The ohmmeter should read zero.
  3. If the readings are not correct, replace the sensor. It is not reparable.

Thermal Switch Test

  1. Unplug the switch. Connect one ohmmeter lead to the gray (or white) wire and the other to the black.
  2. Warm the switch in your hand. The ohmmeter should read zero with the switch at 58-68°F or higher.
  3. Chill the switch with cold water. There should be an ohmmeter reading at 58-SOT or lower.
  4. Replace the switch if the readings are not correct. It is not reparable.

Control Module Test

  1. Unplug the connector for the red and gray wires from the module. Reconnect the red wires with a jumper wire.
  2. Connect a vacuum gauge to the carburetor vacuum port. Run the engine at fast idle and note the vacuum reading. Reconnect the vacuum hose.
  3. Connect the vacuum gauge to the primary (outside) distributor vacuum connection.
  4. Ground the gray (or white) wire from the control module.
  5. Run the engine at fast idle and note the vacuum reading.
  6. Replace the control module if the vacuum reading in Step 5 is not the same or slightly less than that taken in Step 2. The module is not reparable.

ELECTRONIC SPARK CONTROL
System Test

  1. Raise the rear of the car until the rear wheels are clear of the ground by at least 4 in. Support the rear of the car with safety stands, and place blocks in front and back of the front wheels.
    CAUTION: The rear of the car must be firmly supported during this test. If one of the rear wheels should come in contact with the ground while it is turning, the car will move forward very rapidly and unexpectedly.
  2. Disconnect the vacuum hose from the distributor vacuum advance chamber. This is the outer hose on cars with a dual diaphragm.
  3. Connect the hose to a vacuum gauge.
  4. Pour hot water on the temperature-sensing switch to make sure that it is above 65°F. The temperature sensor is located on the right door pillar.
  5. Start the engine, apply the foot brake, and shift the transmission selector lever to Drive.
  6. Slowly release the foot brake and allow the transmission to shift into High (Third) gear.
  7. Have a friend observe die vacuum gauge while you raise the speed of the engine until the speedometer reads 37 mph.
  8. If the system is working properly, there should be no reading on the vacuum gauge until die speedometer reads 37 mph, at which time the vacuum gauge should show a reading.
  9. If the vacuum gauge shows a reading below 37 mph, a component in die electronic spark control system is defective. If the vacuum gauge does not show a reading, even above 37 mph, there is either a defective component in the electronic spark control system, or there is a broken or clogged vacuum passage between the carburetor and the distributor.

Vacuum Passages Check

  1. Disconnect die vacuum hose that runs from the carburetor to the distributor modulator vacuum valve at die vacuum valve. Connect the end of die hose that was just disconnected to a vacuum gauge. Start die engine and keep die transmission selector lever in either the Park or Neutral position. Raise the speed of the engine to about 1500 rpm and observe die reading on the vacuum gauge. If die vacuum gauge shows a reading, this section of the system is OK. If the vacuum gauge does not show a reading, either the vacuum port in die carburetor is plugged or die vacuum hose out of die carburetor is plugged or broken.
  2. Reconnect die vacuum hose that was disconnected in Step 1. Disconnect die vacuum hose coming out of the distributor modulator vacuum valve and connect it to a vacuum gauge. Disconnect die lead wires that run to die distributor modulator. Start the engine and raise die speed of the engine to about 1500 rpm. If die vacuum gauge does not show a reading, die distributor modulator vacuum valve is defective.
  3. On cars with air conditioning, reconnect die vacuum hose to die modulator valve but leave the wires to die valve disconnected. Disconnect the vacuum hose coming out of die second nipple on die distributor control valve. Start the engine and raise die speed of the engine to about 1500 rpm. If the vacuum gauge does not show a reading, the distributor control valve is defective or the hose leading to die valve is plugged or broken.
  4. Reconnect all vacuum lines but leave the lead wires to die distributor modulator vacuum valve disconnected. Disconnect the vacuum hose to the distributor vacuum advance chamber. Connect this hose to a vacuum hose. Start the engine and raise the speed of the engine to about 1500 rpm. Observe die reading on the vacuum gauge. If the gauge does not show a reading, the hose to the distributor vacuum advance chamber is plugged or broken.

Temperature Sensor Test

  1. Disconnect the two wires that run to the temperature sensor. Pour hot water on the sensor to ensure that its temperature is above 65°F. Connect the two leads of an ohmmeter to the two leads from the temperature sensor. At temperatures above 65°F, the ohmmeter should show a reading. Cool the temperature sensor with ice to bring its temperature below 65°F. At temperatures below 49°F, the ohmmeter should not show a reading. If the temperature sensor does not react this way, it is defective.
  2. With the ignition switch turned on, connect the ground wire on a test light to a good metal ground and insert the probe of the light into the connector of the red and yellow wire running to the temperature sensor connector. If the test light does not light, either the wire is defective or the ignition switch is defective.

Speed Sensor Test

  1. Disconnect the wires running from the speed sensor connector. Connect the two leads on an ohmmeter to the two wires running to the speed sensor. At room temperature the ohmmeter should show a reading of about 40-60 ohms.
  2. Disconnect the speed sensor from the speedometer cable. Connect one lead on a ohmmeter to the inside core of the speed sensor and the other to the body of the speed sensor. The ohmmeter should not show a reading.
  3. If the speed sensor does not give these readings, it is defective.

Distributor Modulator Vacuum Valve And Amplifier Test
If the system operation check showed that the electronic spark control system was not operating properly, and if the vacuum passages check OK, and the temperature and speed sensors checked out OK, then the trouble is either in the modulator valve or the amplifier.

  1. Pour hot water on the temperature sensor to ensure that its temperature is above 65°F.
  2. Disconnect the lead wires to the modulator valve at the quick-disconnect connector.
  3. Turn the ignition switch on.
  4. Connect the ground wire on a test light to a good ground and insert the probe end into the two wires leading to the connector to which the wires from the distributor modulator vacuum valve connect. If connecting to one of these wires lights the test light, and the electronic spark control system is not working correctly, the distributor modulator vacuum valve is defective. If connecting to one of these wires does not light the test light, the amplifier is defective.

TRANSMISSION REGULATED SPARK SYSTEM
System Test
MANUAL TRANSMISSION
NOTE: When performing the following tests, be sure that the temperature switch is kept above 65°F, except as noted. On models equipped with a spark delay valve, the spark delay valve must be removed for this test to be valid.

  1. Connect a vacuum gauge between the distributor and the distributor modulator valve, using a T-connector.
  2. Start the engine. With the transmission in Neutral, the vacuum gauge should read zero.
  3. Increase engine speed to between 1,000-1,500 rpm with the clutch pedal depressed. The vacuum reading should remain at zero.
  4. With the clutch still depressed, place the transmission in High gear. Increase engine speed, as before. The vacuum gauge should now read at least 6 in. Hg. If it does not, proceed further with testing. Remember to shift into Neutral or stop the engine before engaging the clutch.
  5. Unfasten the transmission switch lead from the distributor modulator terminal. Connect the lead in series with a low amperage test lamp and the positive side of the battery.
  6. Move the gear shift lever through all of the gears. The test lamp should remain on until High gear is entered.
  7. If the lamp stays on when the transmission is in High, either the switch is defective or the circuit is grounded. If it fails to come on at all, the switch is defective or the circuit has a loose wire.
  8. If the transmission switch is functioning properly but the system check indicates that temperature switch test under "Electronic Spark Control Temperature Sensor Test."