I have a new Garrett stock turbo installed with stock tuning, at idle it goes to 85% and around 30% full throttle, is this acceptable? I have read several articles that say it should never go to 85%

 

Mine gets up to near 80% at idle but 15% or 85% are the numbers I think means the vanes are sticking. If I blip the throttle at idle it settles to around 70 ish. I am sure I have some sticking. I do exercise it regularly and most of my runs are at highway speed and 20 miles long. It may need to be thrashed a bit after you get it up to operating temps.

 

Don't think it is sticking cause it's brand new. Also updated oil feed and drain tubes.

 

This was copied from another post, are the following statements accurate?
Since it's counter-intuitive, here's a little explanation here of how the VGT% works; it's a number that represents the duty cycle of the VGT solenoid. 85% duty cycle equates to the solenoid being fully extended, which closes down the vanes to their tightest configuration. Conversely, 15% duty cycle on the solenoid opens the vanes fully, allowing maximum gas flow towards the turbine wheel.

Keeping the vanes closed (or nearly so) at idle and low engine speeds mimics a tiny turbo that spools quickly and provides little lag. Opening the vanes as engine speed and load rises allows the turbo to act as a larger unit, which is able to produce larger boost flow as the engine requirements increase, without overspeeding a smaller unit, which would result in both overboost and turbine explosive failure over time.

 

Edit - found documentation (below) on VGT operation.

Just remember that the VGT% is a command, not an actual valve position. If the unison ring sticks (or if there is a leak), then the commanded VGT% will change in order to attempt to move the vanes where the PCM wants them.


Also - failed solenoid defaults to the open position, making it difficult to build boost.

 

From Ford -

6.0L Diesel Variable Geometry Turbocharger (VGT)

The variable geometry turbocharger (VGT) allows the PCM to control boost at low and high speeds for improved
response. The vanes inside the turbine side of the turbocharger are electronically controlled and hydraulically
actuated to control the level of boost and the amount of exhaust backpressure.

In the past, most turbochargers could deliver boost only at higher engine speeds and there was a lag time between
pressing the accelerator and turbocharger boost.

The variable geometry turbocharger (VGT), however, allows the PCM to also control boost at low speeds. The
VGT improves the response of the 6.0L diesel engine by reducing turbo lag. This is possible because the vanes
inside the turbine side of the turbocharger are electronically controlled.

• The variable vane design allows the VGT to operate as efficiently as a small turbocharger at low engine speeds
and during engine warmup. It also provides the high boost capability of a large turbocharger at high engine
speeds.
• During engine operation at low engine speeds and load, little energy is available from the exhaust to generate
boost. To maximize the use of available energy, the vanes are closed. In doing so, the exhaust gas is accelerated
between the vanes and across the turbine wheel increasing turbocharger wheel speed and boost. In general, this
allows the turbocharger to behave as a smaller turbocharger.

During engine operation at high engine speeds and load, there is a great deal of energy available in the exhaust.
Excessive boost under high-speed, high-load conditions can negatively affect component durability. The vanes,
therefore, are commanded open to prevent turbocharger overspeed. This, essentially, allows the turbocharger to
act as a large turbocharger, not creating excessive backpressure.

• During engine warmup, the vanes in the turbine side are closed. When the vanes of the turbocharger are closed,
the engine has a higher exhaust backpressure. This creates more heat and quickly warms the engine to its
normal operating temperature.
• During engine operation at moderate engine speeds and load, the vanes are commanded partially open. With the
vanes set to this intermediate position, the VGT can supply the correct amount of boost to the engine for
optimal combustion as well as provide the necessary backpressure for EGR operation.

 

VGT Control Valve

The VGT control valve controls the position of the variable vanes in the turbocharger by metering engine oil to either side of the control valve piston.

The VGT control valve is actuated by the PCM, based on engine speed and load. The function of the VGT control
valve is to open and close the variable vanes inside the VGT.

• The VGT control valve is a variable-position duty-cycle controlled valve and a proportional hydraulic spool
valve.
– The variable geometry turbocharger control valve (VGTCV) is located on top of the turbocharger and can be
serviced separately from the VGT. The control valve allows oil to flow to one side of the piston or the other
side of the piston depending on which way the PCM wants the vanes to move.
– When one side of the piston is pressurized, the opposite side is vented to drain.
– Spring force moves the spool valve to the center closed position.
– When ON signal time increases, the exhaust manifold pressure increases.
• Once the desired turbocharger vane position is obtained, the VGTCV goes to a parked position. Both ports of
the spool valve are blocked and the VGTCV piston remains in the last position.
• The command can be viewed on WDS as VGTDC# and is described in percent closed. A low percent means
the vanes are commanded to an open state. A high percent means the vanes are commanded to a closed state.
– The WDS view shows zero and allows you to command zero, but it is not zero.
– The actual range is approximately 15 to 85 percent.

A cam follower at the end allows the valve to return to a neutral position when the PCM is not using the valve to
move the vanes.

NOTE: If it is disconnected, the valve will default to the vanes open position.
The valve position is controlled by switching the current source inside the PCM. If the valve is disconnected, the
turbocharger vanes remain in an open state.

 

Very informative, thank you very much. Based on your information, at idle the vanes are closed and VGT% should be around 85%. So why do some say it should NEVER read 85% ? This is what I don't understand.

 

Ford states that at low idle the commanded VGT % should be around 73% (for a hot engine). 85% or so would be fine w/ a cold idle.

 

Could this be the problem? Up-pipe

 

Doesn't look like a big leak, but then again your numbers aren't off by much IMO. Good to find and correct any leak though!

 

The gap doesn't look like much but I do have a slight smell of diesel in cab after putting in new turbo. Is it possible to remove the up pipe clamp without removing turbo? The flange where bolt tightens is slightly spread open maybe not allowing enough to tighten. In this photo the gap is slightly bigger at top.

 

Decided to go back and try to better align the up-pipe, loosened the 2 up-pipe bolts and re-clamped the connecting clamp. While doing this installed the blue spring update, fuel pressure went from 50 to 65 psi. Hopefully this will help my VGT reading of 85% at idle.

 

my VGT% at idle in park is 82-83. When i put into drive it drops to 75-78%. on flat ground at WOT best i could get was 34%.

 

After reading lots of old posts, I think the EBP sensor might be part of the problem, going to remove and clean the tube, is there any way to check the sensor?