Sensitive Boost Control

What are some options to dealing with extremely sensitive boost control? I've got a mac 3 port valve running at 30hz. On 0% DC, the car holds a steady 28psi dropping to 27psi by redline. On 15% I hit a perfect 30psi across. 24% holds 34PSI to redline. 25% holds 36PSI, but the moment I go to 27%, the boost goes over 44psi. It becomes uncontrollable in open loop control. This is a 2% increase in duty cycle bringing the boost up over 10psi. Twin 44mm gates, plumbed like the image attached. Stiffest springs, so around 25 psi of springs are inside. Turbo is a next gen 7275 on a 4b11t controlled by AEM Infinity. I wanted to try to do decimals in the boost duty cycle table, but it looks like they get rounded to the nearest 1.

I'm retesting this with a lower pound spring. I'm hoping to still be able to hit ~50psi since the duty cycle was so low with the heavy spring. Will update when I can.

Is the reference pressure to the WG Sol Manifold Pressure or Boost/compressor outlet pressure?

Hi Robert, the reference pressure is coming from the compressor cover.

This is a bit odd as there are not a lot of practical reasons this would happen. If it were the oppsite, you could explain it with too much exhaust back pressure, too light of a spring, not enough WG reference pressure,...

Also, boost creep is where the WG is too small not allowing enough exhaust energy to bypass the turbine resulting in too much boost. In this case you are able to make and maintain a lower steady MAP without requiring significant manipulation to the WG control.

I would start with a general confirmation of the rest of the engine function, especially the VVT system. Since cam timing can cause significant changes in MAP, I would just confirm that you have nothing extra happening here. If that is ok, I would continue with general visual checks of all of the boost related components. Go back through the claibration and check if there are other things happening once you get to a MAP of +40-44psi. Post a complete PC log of both runs if possible.

This 4b11t has both of it's Mivec cams deleted and replaced with fixed ones, so there's no VVT. This car strictly runs on e85, so I'm using the primary lambda and primary timing tables for everything. I'm attaching both maps and both logs. Maybe I have the ignition timing too retarded at high boost levels so the unburned fuel is feeding the turbo too much energy?

And then the boost cut files here:

Can I have the log for the higher boost run? The Boost target stuff is a little weird. Im assuming you were making changes during this log that is not saved in the log. With 4 target tables, one being zero, two having high negative values and it looks like you are only using one table. Now this on its own wont cause the problem you are having. You will be able to clearly see through the map target and WG output, what is actually hapening. If there were issues there, you would see them straight away.

I'm going to fix the boost target tables this weekend. One of them is set to 0 (incorrectly) instead of -14.5, so the target is 14.5 higher than what's in the second table. I use the second table for the main target. Also, the log for the higher boost run is in the above post labeled: 5-2-26-rev3-27DC.itlog. First time doing this after completing the EFI tuning course and practical tuning course, so I'm learning as I go.

Looking through both logs, The first as a Boost base duty table of 26%, Actual duty of 24.9% and an MAP of 35psi.

Second log has Boost base duty table of 27%, actual duty of 30.7% and a MAP of a climbing 44.1psi.

Looking at your notes from the original post, you were seeing pretty significant gains in MAP with small changes in WG duty. The change in duty from 35psi to the 44psi, was almost 7% not the 2% that the table showed. I cant say that I would expect a 9psi change from only 7% in duty but is it possible, Yes.

Ah yes you're right. Ok to add even more clarity. My original map I had set 40psi to 30% duty cycle. That would have been a 5% increase from 35PSI and I was hoping to see 40psi, but boost cut at 44. Then, I had lowered the boost duty cycle to 27% in the revised map, that's why the log isn't matching the numbers in the table. I'm attaching the log at 27% duty cycle here. Sorry about the confusion!

That log only shows a 27% final duty and the MAP going over 44psi. No other pulls. This shows the same issue before just at a lower duty cycle.

Are you able to show this back to back in the same log? One pull, add duty, another pull, see if it cuts. if it does, lower the duty and see what happens. Without seeing this stuff back to back with an A, B, A test, its hard to confirm the problem. If something changed as a whole and you are now not able to make steady boost, just saying it is a duty sensitivity issue is difficult to diagnosis. With problems like this you will want to confirm the condititons that these issues repeat.

Most likely the issue is something mechanical. Additional testing will confirm the problem and what it takes to replicate. From there I will be able to suggest what to check next.

Sounds good. I will update you tomorrow with new data and the A/B/A testing requested.

Hey, sorry for the late response but I have some good news. I dropped the wastegate spring to a 17 pound spring instead of the ~24 pound spring we had inside and have had a much better time controlling the boost. 30% duty cycle is able to hold a perfect 45 PSI across the entire rev range and I will be doing some more tuning this weekend to see if I can dial it in in all gears. I'm hoping since the duty cycle is so low I'll be able to crank it up to 50-55 on kill, but for longevity 45psi is such a great spot! I'll attach the map and log if you or anybody else is interested to take a look!