Help needed with boost control

[swifty]

I have been trying to figure out how to go about resolving a boost oscillating issue with my car. At part throttle accelerating from around 3000rpm to at least 4000rpm the car surges and the boost gauge shows the boost oscillating. The car is a JDM STI 2001 with a standard map and a full decat exhaust. Fuel is either 99 ron straight from the pump or 98 ron plus some octane booster so at least 99.

I have logged stuff like timing, wastegate duty, map etc. and found the target boost is being exceeded at times. Everything else seems ok as far as I can tell.

I have read the tuning boost thread here:
http://forums.openecu.org/viewtopic.php?t=449

Going by the explanation given by CrazyMikie I believe I need to reduce the wastegate duty cycles to prevent it exceeding the target boost and causing the ecu to apply some correction.

My rom http://forums.openecu.org/viewtopic.php?t=456 has a Max Wastegate Duty Cycle map but does not have an Initial Wastegate Duty Map. Therefore, I can only conclude it doesn't have a fixed starting duty (other than zero) so applies the maximum duty for the given rpm and throttle % until it reaches the desired boost then is adjusted some by Turbo Dynamics. Please can someone confirm this or tell me how it works if this is incorrect, thanks.

Also, it has a Turbo Dynamics Proportional Burst and a Turbo Dynamics Proportional Continuous map, but doesn't have Positive or Negative Integral tables.

I would like to be able to understand the relationship between the Max Wastegate Duty Cycle and the Turbo Dynamics maps. My interpretation of this based on what I have read in the other thread is as follows:

Max Wastegate Duty map controls % of time the wastegate allows exhaust gases through the turbo to create boost. Increasing the value means the gases will go through the turbo and create boost for more time so potentially boost will be higher or target boost achieved sooner. Too high a value can cause overboost, ie exceeding the target. Reducing the value means the gases are going through the turbo and creating boost for less time so boost will be lower or target boost will be achieved later, perhaps not at all if reduced too much.

The actual wastegate duty applied for any given rpm/load/target boost will be based on the current boost and wastegate duty. The Turbo Dynamics Proportional Burst map will define how quickly the Wastegate Duty Cycle changes based on these inputs. Please can someone confirm how these changes are made based on the values in the Proportional Burst map. For my car they are:
-0.2bar -9.41%
-0.12bar -1.88%
-0.05bar -0.79%
-0.02bar -0.39%
0.00bar 0.00%
0.00bar 0.00%
0.02bar 0.39%
0.05bar 0.79%
0.12bar 1.88%
0.2bar 9.41%

Does this mean that if I see my car overboosting by +0.2bar then a positive adjustment of +9.41% is applied to the wastegate duty cycle ? Would this not have the effect of increasing boost even further ? I am slightly confused if this is the case.
Perhaps this is completely wrong, and it means to add 0.2bar of boost in an underboosting situation then an adjustment of 9.41% is needed in the duty cycle.

When the target wastegate duty cycle has been reached the Turbo Dynamics Proportional Continuous map is used to check if the Desired Boost has been reached or exceeded and the ecu will modify the wastegate duty cycle to bring the boost back on target. In my case the target is being exceed so it must apply a reduction in the duty cycle. The values are similar to those for the Proportional Burst with the exception of the upper and lower which are only a third of the corresponding values in the Proportional Burst table:

-0.2bar -3.14%
-0.12bar -1.79%
-0.05bar -0.79%
-0.02bar -0.39%
0.00bar 0.00%
0.02bar 0.39%
0.05bar 0.79%
0.12bar 1.79%
0.2bar 3.14%

This would suggest that when the ecu is attempting to reach target boost initially it will make bigger adjustments so as to get to target quicker than when it is trying to maintain a target, it makes smaller adjustments.

So, when I accelerate and the boost gauge shows the boost climb then fall and climb again with a constant throttle opening this is likely to be caused firstly by the Proportional Burst then once target is reached by the Proportional Continuous values. The amount of fluctuation I see is based on these values so if I change the values it will change amount of fluctuation.

The underlying problem is that my Max Wastegate Duty Cycle is causing the target to be exceeded by more than the amount needed to cause the turbo dynamics to intervene to reduce it. Therefore, if I can get the Max Wastegate Duty Cycle to be more accurately matched to the target it will be less likely to exceed the target, or will exceed it by less, requiring less adjustment by Turbo Dynamics so the end result should be smoother acceleration.

Please can someone who has more experience in tuning boost than me comment on this and let me know if it is correct.

Many thanks

[RICK SCHU]

Therefore, if I can get the Max Wastegate Duty Cycle to be more accurately matched to the target it will be less likely to exceed the target, or will exceed it by less, requiring less adjustment by Turbo Dynamics so the end result should be smoother acceleration.

Exactly. You should log rpm, TPS%, boost, WDC% and then try several runs with different throttle positions where you would normally see the spiking. Then lower the WDC% in that TPS column. Start out a lot lower so you can get to a point where you have no spiking at all (spool will be slower). Then ramp it up until you get a spike and then back off a bit.

[swifty]

Thanks

I've lowered most of the higher values by around 20% and smoothed the graph a bit so will see how it goes from there. I have a bit of time this week to do some logging and further adjustment.