HOW IT WORK

The way a VGT turbocharger works is that it adjusts the gas cross section at the inlet of the turbine wheel in order to optimize turbine power with the required load.

At low engine speed and small gas flow, the VGT turbocharger reduces the cross section, increasing turbine power and boost pressure.

At full engine speed/load and high gas flow, the VGT turbocharger increases cross section, avoiding turbocharger overspeed and keeping the boost pressure level required by engine

The cross section modulation can be controlled directly by the compressor pressure through the use of a pressure actuator, or by the engine management system using a vacuum actuator.

To modify the cross section, the VGT turbocharger use a mobile multivane system composed of a number of vanes which pivot on their axis.

The VGT uses a set of adjustable vanes, or nozzles, to direct flow into the turbocharger turbine.

When the vanes are closed, flow is directed tangentially into the turbine wheel.

This imparts maximum energy into the turbine, causing the turbocharger to spin faster.

Closing down the vanes allows for excellent transient response and can also help provide boost at low engine RPM, increasing engine torque backup.

Conversely, when the vanes are opened, they direct flow into the turbine in a more radial direction.

This reduces the angular momentum of the flow going into the wheel, producing less turbine work and ultimately slowing down the turbocharger.

Therefore, at high engine speeds, the vanes can be opened to control boost pressure without wastegating.

This provides excellent fuel economy at high engine speeds.

By closing down the vanes, the turbocharger spins faster, boost pressure increases, and air fuel ratio goes up.

Engine backpressure also increases.

Air fuel ratio and backpressure can therefore be traded off in such a way as to produce maximum fuel economy at all operating points.

Normally, the boost pressure is approx.1000 mbar (760 mmHg)with the operation of VGT actuator and throttle actuator.

However, the boost pressure goes up to 2500 mbar (1875 mmHg) when the turbocharger is at the maximum operation.

BASIC INSPECTION

Before performing the inspection of VGT sol. valve, make sure that the follwing items :

① Incorrect installation position and/or loose vacuum hose

② Check for leakage, breakage, or clogging in vaccum hose to VGT actuator and solenoid valve

③ Pull off the vacuum hose from the VGT sol.valve and check for vacuum from the alternator.

④ Check the mounting direction of MAF sensor and for the leakage of the intake system

CHECK PROCEDURE

1.

The vaccum pressure of VGT sol. valve from the alternator

1)

Test condition :

Keep the engine at 1500 rpm for more than 20 seconds and then perform the measure as it is

2)

Specification : Above 650 mmHg

(1)

Check the VGT actuator diaphragm with the vacuum pump

1)

Replace the VGT actuator If the VGT actuator does not move upward and downward normally.

(2)

Inspect the VGT actuator sticking and lift if the VGT actuator sticks in the closed position or C 029 occurs, the engine or A/T symptoms will occur as follows :

① Engine performance reduction with the black smoke

② Gear shifting failure

1)

Replace the VGT actuator

2.

Throttle solenoid valve

(1)

Disconnect the VGT sol. valve

(2)

Connect the ohmmeter probes to the terminal 1 and the terminal 2 and measure the resistance.

1)

Specification : 14 ~ 17 Ω at 20℃(68℉)

(3)

There will be an audible "click" when the power is connected to the terminal 2 and the ground are connected to the terminal 1.

3.

Atmosphere port filter of VGT sol. valve

If the atmosphere port filter is clogged at the idle condition, the engine runs idles rough with the black smoke.

1)

Clean foreign material from passage inside the VGT sol. valve with cleanser.