I'm running electronic boost control on Tephra V7 96530706 using a GM 3-port and a FP 25 psi WGA on my FP Green HTA 73 turbo. Supporting mods are in my sig. The WGA preload is set so waste gate spring pressure alone maintains boost at 21-22 psi with the WGDC set at 0%. My boost profile is 29 psi @ 4000 RPM with a gradual taper to 25 psi @ 7500 RPM.

If WGDC is between 68 - 98.5% I have smooth linear control of boost to maintain this profile. As soon as WGDC is raised to 99%, boost spikes 4-5 psi, and I lose control. See the data plot attached for exactly what happens.

I'm trying to flatten the boost profile and reduce taper at high RPM. What do I need to do to keep boost under control as WGDC reaches 99%?

 

Check your BCS "Re/De-Activation RPM" under Global Boost Control Settings. Make sure your "Deactivate On Deactivate Off" is set to your fuel cut rpm.

 

Post your wgdc table, before and after change.

 

Very odd, seems that the wastegate is shutting all at once and the turbo has much left in it.
Brainwash idea: I'd give it a little more preload to see if you could get the WGDC in a more "modulating" range i.e.: 70-80%.

 

It's set at 8000 RPM. It is not this because it spikes any time I raise WGDC from 98.5 to 99%. If I raise it to 99% at lower RPM it does the same out of control spike but higher

 

WGDC is in the graph artached to my original post. It's 98.5 before the change and 99% after.

 

I have preloaded WGA by 6mm already to achieve what you suggest. It is at the limit

 

Could this be boost creep? I don't know what it looks like and was hoping a more experienced ebc guru could help diagnose this one.

 

Jay @ Boosted tuning

 

Yes Jay if you see this I would like your opinion please.

 

Jay Or Jamie@Dynotech, English Racing, tscompusa, etc... and all the experienced tuners who often take time to help people on the forums.

PM them it's an interesting issue

 

Have you checked for boost leaks? I have a similar setup to you and it seems as your wgdc is very high for the boost your getting in the mid rpm's. At 5k rpm your at 95% and boost is only 27ish. I would be spiking over 35psi with that wgdc. I know our setups are slightly different but that seems like a big difference. I'm thinking you may have a boost leak and when you finally hit 99% and the wastegate completely closes you are overcoming the boost leak and spiking pressure. Just a thought.

 

And at 99%, because of the latency of BCS, it's not building pressure in the wastegate line and stays shut like it would be at 100%. So at 98%, if it's opening, the pressure created applies a force on the mac valve that make it stay opened longer than 2%. Like there is a minimum physical time the BCS can open (pressure delays the valve from closing). That's why the difference in wastegate efficiency is so big, so when the wastegate shuts, you either overcome a boost leak, or something else is happening in there. Don't know if i'm clear.

(When I say open or closed, see it as you will: it's a 3 way valve. )

 

My FP 25psi WGA does that too. I think it is boost creep from having it preloaded too much. I just always go with lower WGDC there to fix it.

Also, some of what Domyz is saying above is true. MRFRED once mentioned that the boost control system actually works on 2 WGDC steps. ie 96% is 96% but 97% with be 98%, 98% will be 98%, but 99% will be 100%. Its because ECUFlash has the incorrect scaling for WGDC according the MRFRED. Someone should fix that.

 

Yes - you have a point. I'll run a boost leak and GM 3-port check this weekend just to be doubly sure.