Vacuum Piston Control System
- Remove control box cover. Disconnect lower vacuum hose from vacuum piston control solenoid at 3-way joint. Connect vacuum pump. Disconnect upper vacuum hose at manifold vacuum port. Connect a vacuum gauge.
- Start engine and warm to operating temperature (cooling fan comes on). Apply vacuum to solenoid. If vacuum is indicated on gauge, go to step 5). If vacuum is not indicated on gauge, turn ignition off. Disconnect 8-wire connector at control box.
- Start engine. Measure voltage between Yellow (pos.) and Black (neg.) terminals of wire harness. If battery voltage is present, replace solenoid valve. If battery voltage is not present, measure voltage between ground and Yellow wire terminal. If battery voltage is present, repair open in Black wire between control box connector and ground.
- If battery voltage is not present, check warning light on dash and self-diagnosis LED on ECU. If okay, check for open in Yellow wire between control box connector harness and ECU terminal B14.
- If vacuum was indicated on gauge in step 1), quickly increase engine speed to 3000 RPM. Close throttle suddenly. If vacuum indication on gauge briefly decrease, vacuum piston solenoid valve is operating properly. If vacuum does not briefly decrease, turn ignition off.
- Disconnect 8-wire connector at control box. Start engine. While measuring voltage at Yellow (pos.) and Black (neg.) terminals of control box harness, increase engine speed to 3000 RPM and close throttle suddenly. If battery voltage does not decrease momentarily, replace solenoid valve.
- If battery voltage does decrease momentarily, check warning light on dash and self-diagnosis LED on ECU. If okay, substitute a known good ECU. If condition is rectified, replace original ECU.