Strange boost problem - 3SGTE

[Wildcard]

I have a boost issue now that my gen3 3SGTE is back in my car - in third gear the boost curve looks like this:

1bar is normal but the flattening out in the middle is not.

Facts at hand:
* Turbo is a blitz K1-380V, boost curve when motor previously installed was fine
* Fuel pump was changed to Walbro 250LPH model while engine was out
* No boost controller installed, turbo VSV is disabled
* No obvious boost leaks
* Wastegate actuator is not obviously bent - first idea was that it might have got knocked at some stage so the wastegate is slightly open when it should be sealed - however it doesn't visually appear to be moved/damged
* With the actuator disconnected 1.3bar is easily obtained quickly and early in the rev range [this is when I took my foot off]
* Car boosts smoothly - no obvious bucking indicating ignition problems

Lastly, I'm going to try to pressure test the actuator tomorrow to make sure its not opening too early....

Any ideas greatly appreciated as this really has us stumped.....

[fivebob]

Very strange behaviour, but your setup also sounds a bit suspect in the plumbing, or maybe I'm misunderstanding your post

The 0.6bar is usually a sign of the wastgate being connected directly to the turbo as that's about the wastegate actuation pressure, but I'm at a loss to explain why it would then rise past that point. Sticking wategate flap perhaps, but even that doesn't tie in with your description.

* No boost controller installed, turbo VSV is disabled

So you have no boost control at all? I'm reliably informed that the Gen III uses the T-VSV as a boost controller by cycling it at 10Hz, so disabling it without substituting some other form of boost control is not advisable.

Is the T-VSV plumbed into the system or not?

Have you bypassed it and routed the wastegate actuator back to the intake, or is it blocked off?

If it's blocked off, is there a bleed to atmosphere to allow the wastegate to close?

Are you using your PowerFC? I've had issues with mine not working properly and keeping the T-VSV shut and limiting boost, fitting an EBC fixed the problem.

Can't think of anything else to try, you've done all the usual steps to indentify the cause of the problem, but the results just don't seem to make sense

[Wildcard]

Thanks for the response -

Last time I had the engine in, I had a boost controller, but had it turned off because the car would make 1bar without any bleeding by the controller. The actuator on my turbo must therefore not open till higher than the stock ~0.6bar.

So when I put the engine back in, I plumbed in the solenoid as before but with no electronic controller plugged into it [still on the shelf...]. As a last resort I took this completely out, so the plumbing is as follows:



Again, the equivalent of this config [with boost controller installed but off] was working fine previously so I can't spot the problem. Is the way this is blocked off not ideal?

PowerFC is still in cupboard too, using stock ECU atm.

Thanks

[fivebob]

Thanks for the response -

Last time I had the engine in, I had a boost controller, but had it turned off because the car would make 1bar without any bleeding by the controller. The actuator on my turbo must therefore not open till higher than the stock ~0.6bar.

I've heard of this happening before, and the owner having problems getting the boost below 18psi. I suspect there may be something wrong in the actuator, as the K1-380v in my Caldina exhibited the same characteristics as the stock turbo. ie 0.6 bar with the boost controller turned off.

So when I put the engine back in, I plumbed in the solenoid as before but with no electronic controller plugged into it [still on the shelf...]. As a last resort I took this completely out, so the plumbing is as follows:



Again, the equivalent of this config [with boost controller installed but off] was working fine previously so I can't spot the problem. Is the way this is blocked off not ideal?

No not really ideal, there is no bleed to the wastegate to allow the actuator to close, usually this bleed is provided by the shuttle valve, but as you've had the shuttle (solenoid) valve in there in the past and it behaved the same, then maybe it isn't required.

Just to eliminate any possibility of the plumbing being the problem I'd suggest reverting back to the stock setup, ie T-VSV plumbed in and connected. If it works in this configuration, or even replicates your other experiments with the wastegate disconnected, then that would indicate a problem with your actuator or less likely wastegate, so perhaps another actuator could be tried. I have a spare one I can lend you from my K1-380v which was working when I removed the engine, let me know ASAP if you want to borrow it as I'm returning to Aus. this weekend.

[Wildcard]

Cheers Fivebob - So I did what you suggested and re-enabled the factory T/VSV so its plumbed back in like normal.
Now the car will boost without flattening but above about 0.7bar the boost is reasonably rough, fluctuating up/down as it travels to sit at 1bar without too many problems.

Now, I pressure tested the actuator and observed approx how far the wastegate rod moved -

0.4bar 1mm
0.6bar 1mm
0.7bar 4mm
0.8bar 7mm
0.9-1bar 10mm

The fact its moving 1mm at 0.4bar seems to indicate to me there is something wrong and as GT4mike pointed out to me - with exhaust gas pressing on the flapper its going to move more than this...

So:
#1 Actuator rod seems to be moving too early
#2 With T/VSV bleeding off some of the boost early on the 'flat spotting' is now gone
This seems to back up the idea that the actuator arm is somehow bent and is trying to open too early.

As you suggest it does seem strange your bascially identical turbo wouldn't make anywhere near 1bar in these conditions, however another friend of mine with a Gen3 one does - maybe its a restriction issue?

If you agree with the new hypothesis some photos of the actuators position on your turbo would be extremely helpful before you go.....

Thanks a lot

[fivebob]

Cheers Fivebob - So I did what you suggested and re-enabled the factory T/VSV so its plumbed back in like normal.
Now the car will boost without flattening but above about 0.7bar the boost is reasonably rough, fluctuating up/down as it travels to sit at 1bar without too many problems.

Possibly due to the low frequency of the T-VSV, @10Hz it's probably on too long and allowing the wastegate to open too far. If you had a slow acting wastegate that may also contribute.

Now, I pressure tested the actuator and observed approx how far the wastegate rod moved -

0.4bar 1mm
0.6bar 1mm
0.7bar 4mm
0.8bar 7mm
0.9-1bar 10mm

The fact its moving 1mm at 0.4bar seems to indicate to me there is something wrong and as GT4mike pointed out to me - with exhaust gas pressing on the flapper its going to move more than this...

So:
#1 Actuator rod seems to be moving too early

No I'd say it's opening too late, to limit your boost to the factory setting of 0.6bar the wastegate should be fully open at that point, even allowing 2psi drop through the I/C it should be fully open by 0.75bar.

#2 With T/VSV bleeding off some of the boost early on the 'flat spotting' is now gone
This seems to back up the idea that the actuator arm is somehow bent and is trying to open too early.

As you suggest it does seem strange your bascially identical turbo wouldn't make anywhere near 1bar in these conditions, however another friend of mine with a Gen3 one does - maybe its a restriction issue?

If you agree with the new hypothesis some photos of the actuators position on your turbo would be extremely helpful before you go....

As noted above I think it's the opposite of what you theorise, my opinion is that it's probably opening later due to a sticking wastgate or one that has too much resistance. However I will take some photos tomorrow just in case I'm wrong.

One of the reasons for my theory is that it would explain the plateau in your previous setup. Wastgate opens sufficiently to bleed of enough exhaust gas, but as the volume of gas increases the opening in insufficient to control the boost, so it rises accordingly and then your wastgate opens fully keeping the boost at 1Bar.