Open Loop Boost Control (oscillation problem)
 

Figure I create a post, rather than keep sending emails to Cludwig every time I have a question or problem :lol: Chris is awesome to deal with, just don't want to abuse him with so many questions so often; besides, this post might help others at some point.

I am experiencing boost oscillation when using a 4 port mac solenoid on a PS1000 on open loop boost control. There's no boost oscillation if I turn off the open loop boost control map (I do so by setting everything to 0).

The setup consists of two Tial 38mm wastegates with 9 psi springs, and both gates dumping to atmosphere. Boost cut on the haltech is set at 14psi, boost restore at 13psi, with a cut time of 400ms. The haltech open loop boost map is set to achieve 12psi, or at least that's what I am trying to accomplish.

Here's a pic of the oscillation as logged by the haltech:
https://www.rx7club.com/attachment.p...1&d=1394414632


Here's a pic of the open boost map on the haltech:
https://www.rx7club.com/attachment.p...1&d=1394414632


And here's a pic of how I installed the 4 port solenoid:
https://www.rx7club.com/attachment.p...1&d=1394414632


Has anybody experienced anything similar when using open loop boost control on the haltech? I read somewhere, somebody stating that the duty cycle on the 4 port mac solenoid valve is very sensitive, could that be the issue here? The duty cycle changes on the map are very sublte and linear, which leads me to believe that that's not the problem here.

Also, as I was taking snapshots, and writing this post, I had an "eureka moment" Could it be that because the 13psi cell is set to 0, the map is interpolating from 30hz to 0hz when manifold pressure reaches 13.X psi?

I am lost, have been trying to figure this out for a couple of weeks, without much success.

What frequency is the output set at? The 4-port runs a little lower frequency usually. 25 hz is a good start.

Send me your map. You have it running right between 12 and 13 psi which have values of 25-30 and 0 respectively. So it's going to oscillate between those two. Probably need to drop the 12 psi row a bit and raise the 13 a bit.

absolutely

Still got you on the hook, I feel like I should pay you for your support. You have gone above and beyond!!! :icon_tup::icon_tup:

From memory, I think the hz are set at 35, I will send you the map tonight. If I set the the close loop boost map to 25, I get about 10psi. Anything above 25 up to 5000rpms, and I get boost spikes; thats why I raised it up to 30 right at 5000rpms.

Awesome, thanks for the input :icon_tup:

KNONFS i had a very similar issue when setting up my open loop boost control (ps1000)

i am running an EFR internal wastegate turbo (EFR 8374) with the "medium boost" actuator and a 3" exhaust, etc.

anyway, i think the issue is that your haltech is trying to interpolate between your 12psi column and your 13psi column, and the variance between the two columns is too large. raise the 13psi column as ludwig said and lower the 12 column. mine took a little tinkering to get right, but it is now perfect.

your post is from a month ago, so i'm assuming you fixed this, but you can just datalog and do the playback and watch the blue circle or "trace." i bet it will show the blue dot doing a similar motion to what you're seeing on that datalog graph. the boost shoots to 13psi, then sees zero duty and drops down to where it hits the 12psi column where it sees 25% duty, then back up to 13psi, then down, etc. and it can never stabilize because of that big variance.

i'm curious. please post the results!

Thats exactly what it was, I have to check the map, but I believe the key colum was the 13psi, raising it did the trick :icon_tup:

Sorry i didnt respond sooner, I just saw your post :blush:

great. thanks for the update!

Here's a snapshot of the finished open boost map, and a snapshot of the log file. Hope this helps somebody at some point.

https://www.rx7club.com/attachment.p...1&d=1400035532

https://www.rx7club.com/attachment.p...1&d=1400035532

KNONFS, you know you could keep your wastegate at zero a little longer, which should help your boost response. it helped quite a bit on my car.

for example, take the RPM at which your turbo is capable of making "full" (desired) boost with no wastegate intervention, then just set your boost control duty to start happening shortly before that. if it spikes before it settles, lower the RPM start point a little bit.

I have to put more time on it, my primary goal was to have a stable boost, and then move on to closed loop. I sort of did what you are suggesting, CLudwig recommended the same thing when I initially set the controller.

I can't find the log file for it, but basically, I was getting initial boost spike, and after shifting gears. As the map sits, I still get a boost spike after shifting gears (not as bad as if I was to increase the posted duty %), not sure of that's unavoidable or not.

Snapshot of the log showing the boost spike after a WOT gear shift, and a screenshot of the open loop boost map.

https://www.rx7club.com/attachment.p...1&d=1400387587

https://www.rx7club.com/attachment.p...1&d=1400387587

My next troubleshooting step will be to set the -10 column to 0 instead of 100. The car feels much more responsive at part throttle with this map, but the spikes are killing me!

Closed Loop is super easy to set up. A lot less of a hassle than Open Loop. Good Luck.