1979 Honda Prelude Automatic TransFACTORY OEM SERVICE PROCEDURE

1976 Manual Transmission Equipped Models

  1. Turn ignition on and disconnect vacuum hose from distributor advance diaphragm (cold engine). Connect hand-held vacuum pump to hose. Apply at least 15 in. Hg of vacuum to diaphragm. Vacuum should not drop more than 0.8 in. Hg in 20 seconds. If it does, go to step  3).
  2. If vacuum holds, turn ignition off. Vacuum should drop to zero (0). If vacuum drops as indicated, start engine. Vacuum should appear on vacuum gauge at idle. If not, check vacuum port in carburetor for blockage. See Figure.
  3. Disconnect and plug vacuum hose at distributor side of delay valve. Turn ignition on and apply vacuum. If vacuum drops less than 0.8 in. Hg in 20 seconds, replace solenoid valve. If vacuum still drops, replace check valve. Reconnect hose to delay valve and repeat test.
  4. Warm engine to normal operating temperature. There should be no vacuum at idle. If no vacuum is present, go to next step. If vacuum is present, check thermo sensor continuity. If continuity exists, replace thermo sensor. If no continuity exists, replace ignition solenoid valve.
  5. Connect vacuum gauge to advance diaphragm hose. Raise engine speed to 3000 RPM. Vacuum gauge should indicate more than 2 in. Hg of vacuum after 30 seconds.
  6. If vacuum is less than 2 in. Hg, check vacuum at carburetor side of delay valve at 3000 RPM. If vacuum is present, replace delay valve. If no vacuum is present, clean vacuum port at carburetor.
  7. Remove delay valve from vehicle. Connect a hand-held vacuum pump to carburetor side of delay valve and apply vacuum to delay valve. On Black/Yellow delay valve, vacuum should decrease from 15 to 5 in. Hg in 3-10 seconds (4-13 seconds on Black/Blue delay valve). If delay time is incorrect, replace valve.
  8. Attach hand-held vacuum pump to distributor advance diaphragm and start engine. Apply 15 in. Hg to diaphragm. Ignition should advance. If no advance, replace distributor advance diaphragm.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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