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Speed Control Vacuum Supply Test

  1. Disconnect Speed Control (S/C) servo vacuum hose. Connect vacuum gauge to disconnected vacuum hose. Start engine and observe vacuum gauge reading.
  2. If vacuum gauge indicates less than 10 in. Hg., check for leaks in vacuum line from intake manifold. Repair or replace as necessary. Also check that engine vacuum at manifold is not less than 10 in. Hg. If engine vacuum is less than 10 in. Hg., repair engine performance problem.
  3. If vacuum hose to engine from servo is not leaking, check for leaking vacuum reservoir. Disconnect vacuum hose at vacuum reservoir. Connect a hand vacuum pump to reservoir nipple. Apply vacuum to reservoir and ensure vacuum does not leak. If vacuum leaks, replace reservoir.
  4. Check for faulty one-way check valve located between vacuum reservoir and intake manifold. Remove one-way check valve, and connect hand vacuum pump to reservoir end of valve. Apply vacuum to valve. Vacuum should hold. If vacuum leaks down, replace one-way check valve.
  5. Connect hand vacuum pump to intake manifold end of valve. Apply vacuum to valve. Vacuum should not be able to be applied to valve. If vacuum holds, replace one-way check valve.
  6. With hand vacuum pump connected to intake manifold end of valve, plug opposite end and apply vacuum to valve. Vacuum should hold. If vacuum leaks down, replace one-way check valve.
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