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Home >> Plymouth >> 1978 >> Sapporo 2.6L Eng VIN F, Automatic Trans >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Ignition Timing Control System >> Testing >> THERMO Valve >> 1977 Models
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1977 Models

  1. With engine cold, disconnect all vacuum hoses from thermo valve. With vacuum pump connected to valve fitting No. 1, no vacuum should be produced. If vacuum is produced, internal valve "C" is stuck in closed position or passage is clogged.
  2. With vacuum pump connected to valve fitting No. 3, no vacuum should be produced. If vacuum is produced, internal valve "B" is stuck in closed position or passage is clogged.
  3. Connect vacuum pump to valve fitting No. 4, operate valve, and raise vacuum to 8-11 in. Hg. If there is no vacuum drop or leak, thermo valve is working properly.
  4. Run engine at fast idle until coolant temperature rises to at least 140°F (60°C) and connect vacuum pump to valve fitting No. 1. If vacuum rises, thermo valve is working properly.
  5. Connect vacuum pump to valve fitting No. 3 and operate valve. If vacuum rises, thermo valve is working properly. If vacuum does not rise, valve is stuck open and should be replaced.
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