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Home >> Ford >> 1984 >> Ranger 2.0 C >> Repair and Diagnosis >> Engine Performance >> System >> 2.0/2.3L MCU Testing >> Testing >> Test 5 - Code 44 >> Thermactor System
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Thermactor System

Components controlled by the MCU system in this test are the thermactor air by-pass (TAB), thermactor air diverter (TAD), thermactor air valve, oxygen sensor, carburetor, and MCU module. Components which are not controlled by the MCU system, but could cause code fault are: faulty carburetor (high float level or no power to choke plate), misfiring spark plugs (coil or distributor), restricted air cleaner, restricted PVS and/or faulty air pump (belt or pulley). Anything which adds fuel, restricts air, or inhibits thermactor system from switching air "upstream" to exhaust manifold should be investigated as possible cause.

  1. Remove vacuum hose from TAB valve and connect gauge to hose. Start engine and increase speed to above 2500 RPM to activate "Functional Test". Observe vacuum gauge during initial pulses. If vacuum pulses are above and below or remain above 5 in. Hg, proceed to next step. If pulses are always below 5 in. Hg, proceed to step 7 .
  2. Reconnect hose to TAB valve. Disconnect hose at TAD valve and connect vacuum gauge to hose. Start engine and raise speed above 2500 RPM to start "Functional Test". Observe vacuum readings. If vacuum pulses are above and below or remain above 5 in. Hg, go to next step. If pulses are always below 5 in. Hg, go to step  11 .
  3. Reconnect hose to TAD valve. Remove upstream air hose at TAD valve. Start engine and raise speed above 2500 RPM to activate "Functional Test". Check for air at TAD nipple 20 seconds after initialization (air will last for about 6 seconds). If air is present, thermactor system is operating properly, go to next step. If air is not present at TAD outlet, check thermactor air system.
  4. Turn engine off and reconnect air hose. Disconnect harness from oxygen sensor and jumper harness (circuit 94) to ground. Start engine, increase RPM to initiate self-test (2 or 3 pulses on VOM connected to diagnostic connector). Maintain RPM until diagnostic codes are received (ignore any pulses longer than 1 second). If code 41 is read on voltmeter, check choke system, then go to next step. If code 44 is received, replace MCU and retest.
  5. With oxygen sensor harness disconnected, place DVOM selector in lowest voltage position and connect it between sensor and ground. Start engine and run at 2000 RPM for 1 minute to warm up sensor. Turn engine off and immediately check DVOM. If voltage is less than 0.4 volts, check carburetor (too rich). If voltage is 0.4 volts or more, go to next step.
  6. Immediately purge exhaust system. Disconnect coil "horseshoe" connector and crank engine for 10 seconds with throttle wide open. Observe DVOM immediately after cranking. If voltage is 0.4 volts or more, replace oxygen sensor and retest. If voltage is less than 0.4 volts, MCU system is operating properly, check non-controlled components.
  7. Check vacuum hose between TAD and TAB solenoid, then between vacuum source and TAB solenoid. Repair as necessary and retest. If hoses are okay, go to next step.
  8. Check temperature vacuum switch (TVS) and retard delay valve (RDV) for proper installation and operation. Check vacuum schematic for usage and location. Service valves if necessary, otherwise go to next step.
  9. Check at TAB solenoid output to be sure vacuum is present when the solenoid is energized (12 volts applied). If vacuum is not present, replace TAB solenoid. If vacuum is present, go to next step.
  10. Disconnect MCU connector, then connectors at TAD and TAB solenoids. Check continuity between MCU connector pin 20 and TAD solenoid, then between pin 9 and TAB solenoid. If resistance is 5 ohms or less, replace MCU and retest. If greater than 5 ohms resistance is measured, repair wiring and retest.
  11. Check vacuum hoses between TAD valve and TAD solenoid, then between TAD solenoid and vacuum source. Repair if necessary and retest. If vacuum source and hoses are okay, go to next step.
  12. Check retard delay valve (RDV) for proper installation and operation. Check temperature vacuum switch (TVS) for proper installation and operation (if used). Replace if necessary and retest. If okay, go to next step.
  13. Measure resistance of TAD solenoid. If not between 50-110 ohms, replace solenoid and retest. If resistance is okay, go to next step.
  14. Check at TAD solenoid output to be sure vacuum is present when solenoid is energized (12 volts applied). If vacuum is not present, replace solenoid and retest. If vacuum is present, go to next step.
  15. Disconnect wiring at TAD solenoid and MCU. Measure between MCU pin 20 and TAD solenoid, then between pin 10 and solenoid. If resistance is greater than 5 ohms, repair wiring and retest. If 5 ohms or less, replace MCU module and retest.
Fig 1: Code 44 Wiring Diagram
G9127
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