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Ej20, ej20G, EJ257, exhaust, gc8, Intake, Intercooler, JDM, STi, Subaru, TMIC, Tuning, Turbo, UK, USDM, WRX

Wastegate and Boost Creep FAQ

Wastegate and Boost Creep FAQ

What is Boost Creep?

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.

Wastegate and Boost Creep FAQ: A stock Subaru turbo with the internal wastegate and stock actuator.
Wastegate and Boost Creep FAQ: A stock Subaru turbo.

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.

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Ej20, ej20G, EJ25, EJ257, gc8, Intake, Intercooler, JDM, STi, Subaru, TMIC, Turbo, UK, USDM, WRX

Boost control systems on a Turbo Subaru:

Boost control system on a Turbo Subaru:

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.

Boost Issues:

Is the boost control system connected correctly:

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2.5RS, AWD, Drivetrain, forester, Impreza, Legacy, STi, Subaru, Suspension, Transmission, UK, USDM, WRX

Axle general maintenance:

Axle general maintenance:

Front stub axle seal replacements require special precautions. The seals are pressed into a side bearing retainer, which must be removed to replace a leaking seal. The side bearing retainers also control front differential side bearing preload, as well as ring and pinion backlash.

When replacing a stub axle seal, mark the position of the side bearing retainer before un-threading the retainer. Remove only one side bearing retainer at a time, or you’ll risk disturbing the differential adjustments. If you’ve marked the position before removal, the correctly installed position of the side bearing retainer will be obvious, as you will be unable to turn the retainer another complete turn.

2008-Subaru-Impreza-WRX-Hatchback-Front-Axle-Parts-Assembly
Axle general maintenance: A driveaxle for a 2008 Subaru Impreza WRX.

The driveaxles on some Subaru vehicles are pressed into the wheel hub with a light press fit. Blasting the axle out of the hub with an air chisel, center punch or other implement of destruction invites damage to the wheel bearings. All of the force brought to bear by these methods finds its way to the wheel bearings, possibly damaging their races or balls. Special tools are available for removing and installing  press-fit driveaxles. Ignoring these cautions invites a comeback for noisy wheel bearings shortly after your CV axle repair work.

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2.5RS, AWD, Ej20, ej20G, forester, gc8, Impreza, JDM, Legacy, UK, WRX

ABS for Early Subaru Part 4:

ABS Brake System for Early Subaru Part 4:

Troubleshooting Process:

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.

ABS Brake System for Early Subaru Part 4: The Subaru Legacy RS was known for using this ABS System.
ABS Brake System for Early Subaru Part 4: The Subaru Legacy RS was known for using this ABS System.

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.

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2.5RS, forester, gc8, Impreza, JDM, Legacy, STi, UK, USDM, WRX

Headlight aiming basics for Subarus:

Headlight aiming basics for Subarus:

Subaru models equipped with aerodynamic headlights require no special fixtures for headlight alignment. Each headlight is equipped with a built-in headlight aiming mechanism. The following sequence demonstrates the correct technique for adjusting the headlights on a Subaru Legacy equipped with aerodynamic headlights.

Headlight aiming basics for Subarus: Some basic headlight adjusting techniques for Subaru cars.
Headlight aiming basics for Subarus: Some basic headlight adjusting techniques for Subaru cars.

1.) Turn off the headlight before adjusting headlight aiming. If the light is necessary to check aiming, do not turn on the headlights for more than two minutes.

2.) Inspect the area around the headlight for any damage. If the vehicle has been involved in an accident, it may not be possible to properly adjust the headlights until the damage has been professionally repaired.

3.)The vehicle must be parked on level ground and all four tires must be properly inflated.

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AWD, forester, gc8, Impreza, STi, Subaru, Suspension, UK, USDM, WRX

Maintenance: Subaru Periodic Maintenance Part 4:

Maintenance: Subaru Periodic Maintenance Part 4:

Steering and Suspension:

Steering and suspension parts are a lot like the brake system components. Their proper operation is vitally important to the safety of the driver and his passengers, but it is very difficult to determine how long it will be before any of these components will require attention. That’s why an inspection of all steering and suspension components is required at 15 month/15,000 mile intervals. Changes to these systems may be too gradual for the driver to even notice, leaving it to you to ferret out and correct any wear or damage that has taken place.

Maintenance:Subaru Periodic Maintenance Part 4: Regular checks of the steering and suspension is important.
Maintenance:Subaru Periodic Maintenance Part 4: Regular checks of the steering and suspension is important.

We won’t cover all of the steering and suspension checks here. There’s too much variation between different Subaru models to do an adequate job. What you’re looking for is anything that reduces the original precision of the steering and suspension systems. Perhaps the steering has a little too much play in it or the shocks and struts don’t handle the bumps in the road as well as they did when new. Specific tests for the Subaru model you’re working on can be found in the service manual.

Check the power steering system for dampness or other signs of fluid leakage. The power steering pump reservoir is a good place to start. If the reservoir is low, the fluid has probably leaked out, as it has no place else to go. Approved fluids for the power steering system include Dexron II, IIE or III.


GENUINE OEM SUBARU ATF-HP P/S FLUID QUART BOTTLE

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AWD, Drivetrain, EJ257, Impreza, STi, Subaru, Suspension, UK, USDM, WRX

Rear strut brace install on Subaru WRX/STi 08+:

Rear strut brace install on Subaru WRX/STi 08+:

This is a step by step guide on how to install a rear strut brace in a 2008+ Subaru WRX/STi. Installing a rear strut brace on a 2008+ WRX/STi is more much more involved than installing a front brace. The chassis is significantly different than the new-age 02-07 Subaru Impreza. The need to cut clearances into the floor for the left and right brackets increases the difficulty for this install.

1.) Only work on one strut tower at a time. Only loosen one set of nuts at a time, and do not put the car up on lifts, jacks, or anything else that lifts the tires off the ground. All of these precautions are to minimize changes to the alignment while working on the installation.

2.) Loosen the left and right hinges on the rear strut brace using the 17mm socket and the 8mm allen head wrench. You want to be able to move the brace around as you attach each side bracket to the car’s strut towers.

3.) Remove the hatch floor and set it aside.

Rear strut brace install on Subaru WRX/STi 08+: Remove the rear floor.
Rear strut brace install on Subaru WRX/STi 08+: Remove the rear floor.

4.) Remove the left and right panels from the wheel covering so that you’ll have access to the tops of the strut towers. Working your finger tips under the edge of the panel and carefully working my way around the edges while pulling away from the wheel cover worked best without requiring any special tools. It also helped avoid scratching the plastic.

Rear strut brace install on Subaru WRX/STi 08+: Remove these panels both both sides with your hands. If you can't do that gently use a screwdriver to remove.
Rear strut brace install on Subaru WRX/STi 08+: Remove these panels both both sides with your hands. If you can’t do that gently use a screwdriver to remove.
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AWD, Ej20, ej20G, forester, gc8, Impreza, Legacy, Subaru, UK, USDM, wrc, WRX

Antilock Brake System for Early Subaru Part 3:

Antilock Brake System for Early Subaru Part 3:

Damping Oscillations:

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.

Antilock Brake System for Early Subaru Part 3: The Legacy RS rally car benefited greatly from having a superior ABS unit.
Antilock Brake System for Early Subaru Part 3: The Legacy RS rally car benefited greatly from having a superior ABS unit.

 

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.

Normal Braking:

• 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

Pressure-Reduce:

• 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.

Pressure-Hold:

• 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.

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