The picture below of this paragraph shows the location of piston size and main journal size information on all Subaru engines. As the figure illustrates, it is possible to have more than one piston size in the same engine.
Subaru’s power steering system contains a pump, hydraulic line, and a gearbox (rack). The hydraulic pump is a vane-type pump driven by the engine. It provides pressurized fluid for the system.
Oil Pump Operation
The pump has two internal valves: a flow control valve and a relief valve. The flow control valve regulates the volume of power steering fluid delivered to the rack. During high engine rpm, the pressure in the pump overcomes the flow control valve spring. The control valve slides back to close off an oil passage to the rack and to open an oil return port to the pump inlet. This reduces the power assist to the rack during high speeds, improving the steering wheel feel and response.
The common causes for overboost or underboost: This is a basic guide on the possible causes and some solutions to those causes of a overboost or a underboost situation in a turbocharged subaru.
1.) Decat + High flow induction – Cure: Reduction of the solenoid duty cycle or alteration of restrictor size will help return boost output to its normal level.
2.) Split, poor fitting, or disconnected pipes – Cure: Replace or refit pipes, the pipes that will cause this issue are between the wastegate actuator, solenoid, and the turbo. Including up to the restrictor on the return pipe of the 3 port solenoid.
3.) Manual Boost Controller – Electronic Boost Controller set too high – Cure: Don’t be so greedy and back the boost duty/adjuster off to a safe level.
4.) Restrictor Pill not fitted / size incorrect – Cure: Ensure restrictor pill is fitted (3 port) if so on a 3 port reduce the restrictor size and on the 2 port increase the restrictor size to reduce the boost to a safe level.
5.) Clogged 3-port solenoid: It is possible that the flow of air through the 3-port solenoid could be restricted between the turbo outlet port and the wastegate actuator port if the solenoid is very dirty (usually oil vapor from the intake system), this allows the wastegate to remain clamped shut longer than it should be causing a potential overboost situation. Cure: Clean with carb or clutch/brake cleaner.
6.)Loss of solenoid funcation: Although this is not bverboost it shows itself with very simmilar symptoms, its an interesting scenario. It is possible for the solenoid to fail or even stick shut while under boost. This will result in a rapid reduction of boost pressure to wastegate pressure approx 0.5 BAR. So if you were running at full boost 1.0 BAR for example and the solenoid was to fail shut it would feel just like overboost as the wastegate rapidly opens due to the solenoid blocking off the spill from the wastegate. Cure: Either clean the solenoid with carb or clutch+brake cleaner or replace the solenoid.
Boost creep is a situation where your wastegate port is not large enough to allow the exhaust gas to bypass the turbo. What happens is the exhaust gas will choke the wastegate port preventing further gas flow through the port. Then, the exhaust gas has to take the path of least resistance which is through the turbine of the turbo. This will spool the turbo ‘uncontrolled’ beyond your normal controlled max boost level.
The turbo will be spooling past wastegate spring rate pressure even though the wastegate is fully open thus it is uncontrolled. The best way to check for boost creep is to connect the turbo outlet port directly to the wastegate actuator port and go for a drive. In 4th gear you should normally get a stable boost level of about 0.5 BAR, if you have boost creep the boost will hit 0.5 BAR and will continue to rise with rpm until you either back off or hit overboost fuel cut.
Boost creep should only be present on a turbo that has very little restriction. For example a fully de-catted and high flow induction. It’s been found that the fast spooling IHI VF35 is very prone to boost creep. The cure is to remove the turbo and enlarge the wastegate port. Then, fit a stronger actuator 0.75 BAR the reason for this is because you have made the wastegate port larger. The effective size of the wastegate plate acting against the exhaust gas flow is larger which allows the exhaust gas excert more force on the wastegate plate.
This in effect weakens the effectiveness of the actuator. Before the increase in size of your wastegate port the actuator would open at 0.5 BAR, after the increase the actuator would open earlier at 0.3–0.4 BAR. After these changes are made to the turbo either a boost controller or a remap (to adjust solenoid duty cycle) should be sought to control the boost to a safe level.
This guide covers most boost related issues including a short introduction on how your boost systems work. This information is based on the Classic Impreza’s, but will cover the newer WRX/STi cars to a certain extent.
Safe boost levels:
When modding your car without mapping (full de-cat and high flow induction etc) you increase the efficiency of your turbo which could result in engine damage due to lean running at high rpm / max boost. To prevent damage always try and keep your boost level as close to standard as possible until your car is mapped for the increase in boost pressure.
TLDR: Don’t screw with your boost levels until you get the car tuned by someone who knows what they are doing. Otherwise you’ll probably end up with a blown up Subaru.
To troubleshoot ABS systems, it’s best to follow a step-by-step procedure like the one on the 1992 Legacy ABS-2E Service Manual Supplement. Enter the flow diagram with the symptom reported on the repair order.
The diagram calls that Trouble Occurs. The first step in the procedure is “Basic Checks.” This calls for a visual inspection to look for obvious problems and includes the following items:
• improper battery voltage
• low brake fluid level
• brake fluid leaks
• brake drag
• condition of the brake pads and rotors
• size, type, and condition of the tires (Check the tires to confirm that they are the correct tires for the vehicle, that they are in good condition, and that they are inflated to the correct pressure).
If you find something wrong at this stage, correct it and see whether it eliminates the reported symptom. If not, continue to Step 3. Step 3 is Self-diagnosis. At this time, put the ECU into self-diagnostic mode, and monitor the ABS warning lamp for trouble codes.
An additional benefit of this arrangement is that the mechanical valve damps out some of the unwanted oscillation in the brake pedal as the ABS pump runs. Because of this, the F valve used on the ABS-2SL system is no longer needed and has been eliminated from the circuit.
ABS Operating Modes:
To illustrate the four operating modes of this ABS system, we’ll assume that the ECU is operating only the solenoid for the right rear brake circuit. Recall that this circuit also affects the left rear brake circuit through the mechanical valve.
• Driver depressing pedal
• ECU passive (monitoring)
• Zero current in solenoid valves
• Pump off
• Plunger piston full right, pressure port open
• Master cylinder pressure supplied to all wheel cylinders
• Pump pressure raising pedal
• ECU controlling solenoid valves and pump
• Full current in the right rear solenoid valve
• Pump running
• Plunger piston moves left, closes pressure port; system balances the two rear wheel cylinders.
• Pedal firm
• ECU controlling solenoid valves and pump
• Half current in the right rear solenoid valve
• Pump Off
• Pressure port closed
• Plunger piston is stationary, maintains reduced pressure in the right and left rear wheel circuits.
A variety of antilock brake system (ABS) have been installed in Subaru vehicles since the first systems were installed in the 1990 Legacy. In the sections that follow, we’ll give you a brief overview of each system and explain proper diagnostic techniques.
The original Subaru Legacy Antilock Brake System (ABS) was licensed by Bosch and manufactured by Nippon ABS, Ltd. The system electronically controls brake fluid pressure supplied to the brake system. This control helps to prevent “wheel lockup” during braking on slippery surfaces and emergency situations. The system includes a fail-safe feature, which indicates a malfunction by illuminating the warning lamp. The system is then returned to a conventional power brake system. The four channel system provides accurate individual wheelspeed control and improves the directional stability of the vehicle during braking.
A tone wheel is attached to each wheel hub and rotates at the same speed as the hub. The magnetic speed sensor is mounted in the axle housing. The notched tone wheel acts as a reluctor which modulates the magnetic field of the speed sensor. The tone wheels are individually replaceable.
The speed sensor provides an alternating voltage signal to the ECU. The alternating voltage and frequency corresponds to wheelspeed.