Purpose, Function
By lengthening the exhaust passage, the transmission of exhaust pressure waves to other cylinders can be delayed, and the amount of gas exhausted from a cylinder and forced back inside the combustion chamber is reduced By reducing the residual gas, the temperature inside the combustion chamber is reduced and the occurrence of knocking even at a high compression ratio is inhibited.
Construction
The exhaust manifold is installed to the rear of the engine. In addition, the catalytic converter (WU-TWC) is integrated (WU-TWC).

When the No.1 cylinder is at the intake stroke, the No.3 cylinder is at the exhaust stroke. By inducing the high temperature gas exhausted from the No.3 cylinder into the No.1 cylinder, the high temperature gas in the No.1 cylinder remains. If the amount of residual gas is high, the temperature in the combustion chamber rises and knocking can easily occur. With the 4-2-1 exhaust system, the transmission of exhaust pressure waves between each cylinder is delayed by the long exhaust pipes.

Exhaust System Removal/InstallationFuel Injector Relay
Purpose, Function
Supplies power to the PCM for the fuel injector and spill valve control solenoid
valve operation.
Construction
The fuel injector relay is installed in the relay and fuse block.
Operation
When the ignition is switched ON, the battery voltage ...
On/Off Solenoid Removal/Installation [Fw6 A EL, Fw6 Ax EL]
WARNING:
A hot transaxle and ATF can cause severe burns. Turn off the engine and wait
until they are cool.
Always wear protective eye wear when using the air compressor. If the air
compressor is used, any particles of dirt or soiling could spatter and get into
the eyes.
...
Pressure Sensor Removal/Installation [Two Step Deployment Control System]
WARNING:
Handling the pressure sensor improperly can accidentally operate (deploy)
the air bag module, which may seriously injure you. Read the air bag system
service warnings and cautions before handling the pressure sensor..
1. Switch the ignition to off.
2. Disconnect the ne ...