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Test 10 - Choke System Check

NOTE: The following tests must begin with the engine cold.
  1. Set accelerator linkage to the proper start position. Remove air cleaner. Check choke plate and fast idle cam position. Choke plate should be in fully closed position and fast idle screw should be on the highest step of the fast idle cam. If choke and cam position are okay, proceed to step 2). If choke is not fully closed or cam is not in position, check for choke plate sticking or binding. Repair choke and linkage as required.
  2. Remove air cleaner. Set fast idle speed screw on the highest step of the fast idle cam. Remove vacuum hose from choke diaphragm. Connect an auxiliary vacuum supply to choke diaphragm. Apply 15 in. Hg of vacuum. Measure clearance between top of choke plate and air horn wall.
  3. Vacuum should hold at applied setting and choke plate should be in proper position of vacuum kick specifications. If vacuum holds and choke vacuum kick is within specifications, proceed to step 4). If vacuum does not hold, replace choke vacuum kick diaphragm. If vacuum holds and choke vacuum kick is not within specifications, adjust as required.
  4. Disconnect air duct from air cleaner snorkel. Disconnect vacuum supply hose to heated air intake system air temperature sensor. Apply 15 in. Hg of vacuum.
  5. Vacuum should close heated air door when air temperature is below 76°F (25°C) and then slowly bleed down, opening the heated air door.
  6. If vacuum builds up, closes the heated air door and then bleeds down, proceed to step 7). If vacuum builds up but heated air door does not close, repair or replace door as necessary. If vacuum does not build up or does not bleed down, replace air temperature sensor. If vacuum builds up, bleeds down, but heated air door does not open, repair or replace door as required.
    Fig 1: Coolant Sensor Terminals
    G5758
  7. Disconnect coolant sensor. Connect an ohmmeter between terminals No. 1 and 3 of the coolant sensor. Ohmmeter should read as follows: below 150°F (66°C), 20-200 ohms; from 150 to 200°F (66 to 93°C), 100-1500 ohms; and above 200°F (93°C), 400-6000 ohms. If resistance is okay, proceed to step 8). If resistance is not okay, replace coolant sensor.
  8. With coolant sensor connector disconnected and ohmmeter connected between terminals No. 1 and 2 of the coolant sensor, ohmmeter should read as follows: from -40 to 20°F (-60 to -6.7°C), 22,000-382,000 ohms; from 50 to 100°F (10 to 38°C), 3300-36,000 ohms; and from 140 to 245°F (60 to 118°C), 176-3900 ohms. If resistance is okay, proceed to step 9). If resistance is not okay, replace coolant sensor.
  9. On all models, disconnect CVSCC valve at vacuum hose connector. Connect a vacuum pump to valve. Apply at least 10 in. Hg of vacuum. Vacuum should hold engine coolant temperature below 125°F (52°C). If vacuum is okay, proceed to step 10). If vacuum does not hold, replace CVSCC valve.
    Fig 2: CVSCC Valve
    G5755
  10. Remove air cleaner. Start engine. Observe position of choke plate. Choke plate should open partially from a fully closed position. If choke plate is in proper position, proceed to step 11). If choke plate is not in proper position, proceed to step 13).
  11. Connect a voltmeter to the choke connector and ground. Voltage reading should be within one volt of battery voltage. If voltage is okay, proceed to DRIVEABILITY TEST 16. If voltage is not okay, turn the ignition off. Remove connector from the oil pressure switch. Connect a voltmeter to the oil pressure switch terminal "C" and ground. Turn the ignition switch to the "RUN" position.
  12. Voltage reading should be within one volt of battery voltage. If voltage is not okay, check harness to the ignition switch for an open circuit. If voltage is okay, turn the ignition off. Connect an ohmmeter between the oil pressure switch connector terminal "A" and the choke connector. Ohmmeter reading should show continuity with zero resistance. If there is continuity, replace the oil pressure switch. If there is no continuity, repair harness for an open circuit.
    Fig 3: Engine Harness Connector
    G3990
  13. Disconnect the vacuum hose from the choke vacuum kick diaphragm. Connect a vacuum gauge to the hose. Start the engine. Vacuum gauge should read manifold vacuum. If vacuum reading is okay, repair choke linkage. If vacuum is not okay, check and repair vacuum source from the carburetor.
NOTE: Some engines use a thermo vacuum delay valve in this hose. If the ambient temperature is more than 45°F (7°C), a 10 second vacuum delay will occur. There is no vacuum delay at temperatures below 45°F (7°C). Also some engines may use a choke pull-off delay valve.
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