Federal 4WD Models

On 4WD models with manual transmission, fresh air is supplied to the exhaust ports on the No. 2/No. 4 and No. 1/No. 3 cylinder sides by 2 air suction valves (ASV-III). Since ASV-III does not have a cut-off valve, it operates continuously.

On 4WD models with automatic transmission, fresh air is supplied to the exhaust ports of No. 1/No. 3 cylinder sides by ASV-I with cut-off valve. Fresh air is supplied to exhaust ports of No. 2/No. 4 cylinder sides by ASV-III without cut-off valve. See Fig 1 .

On automatic transmission models, the exhaust gas pulsation is transmitted to the ASV-I through the air suction pipe. When negative exhaust pressure (vacuum) is transferred to the ASV-I, the reeds of the air suction valve are opened and fresh air from the TAC is sucked into the exhaust passage. When positive pressure reaches the ASV-I, the reeds are closed to prevent reverse flow of exhaust gas.

The ASV-I fitted on the No. 1/No. 3 cylinder side is controlled by the revolution sensor and solenoid valve I. If engine speed is less than the set level, solenoid valve I is opened by revolution sensor and cut-off valve is opened by intake manifold vacuum, thus operating the ASV-I.

If engine speed exceeds the set level, solenoid valve I is closed by a signal sent from revolution sensor and cut-off valve is closed, deactivating ASV-I. Under low vacuum conditions (such as wide open throttle), the check valve II closes the vacuum circuit to hold cut-off valve open during this condition. See Fig 1 .