Boost Pressure graphing looks strange...

Discussion of tuning specific to MAZDASPEED6/MAZDASPEED Atenza/Mazda 6 MPS vehicles
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Lolmooses
Posts: 43
Joined: June 16th, 2020, 1:53 pm

Boost Pressure graphing looks strange...

Post by Lolmooses »

Hello there, I've started getting very close to stock MAP sensor limits, sometimes hitting boost cut and know I notice my boost pressure looks like digital waveforms instead of a nice smooth climb and descent like it used to be. It no longer exactly tracks absolute pressure. Anyone ever seen this before? I have a CS 3.5 MAP sensor ordered, but curious to see what others have to say (and by others I mean Mituc since you're the only person I see post around here usually hahaha).

Also had an instance today where absolute pressure was reading properly but boost pressure was at -11 from 4000-4700 or so and then it started tracking absolute. AFR plummeted to the 8's and 9's during the -11 boost reading as well, big loss of power resulting.

https://ibb.co/qdBGgrB <- Weird Reading
https://ibb.co/7QY3gCQ <- Normal Reading
2006 MS6: CS HPFP internals, stage 2 CS intake, CP-E TMIC, CS catback with racepipe, GFB hybrid BOV, CS EBCS
mituc
VersaTuner guru
Posts: 1323
Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: Boost Pressure graphing looks strange...

Post by mituc »

Both links you posted are broken.
However what you're describing sounds somehow familiar. The boost graph will look like a wave rather than a curve/line when corrections are applied. These corrections are applied to maintain the load around the target or because limits are hit.
Also, once you approach the boost limit of the factory MAP sensor (255kPa/36.98PSI) sometimes the readings may not that accurate any more, especially around or above 248-250kPa, but you can still rely on the limit there if you set it to a value above 250kPa but not higher than like 254kPa (which I don't recommend).

I usually don't monitor boost because that is MAP-BARO so it depends on the barometric pressure in your area. Because all the limits in the calibration tables are for absolute pressure boost is just something to compare when you speak with people tuning for just boost on other platforms, or just to make a statement easier to digest, like it's easier to understand something like "my boost limit is at 19PSI" instead of "my MAP limit is at 34PSI).

As for the happening you were talking about, it sounds like a cut. Post a log with that one (in .csv format) if you logged that event.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
Lolmooses
Posts: 43
Joined: June 16th, 2020, 1:53 pm

Re: Boost Pressure graphing looks strange...

Post by Lolmooses »

Hmmm I see what you're saying, but the strange thing is my boost PID graphing looks like a wave all the time now regardless of whether I'm doing WOT pulls or just cruising around. I posted some pictures and a CSV of that pull.

Image <- Cruising
Image<- WOT Pull
Image<- Normal before this started happening
Attachments
Weird Pull.csv
(1.84 KiB) Downloaded 189 times
2006 MS6: CS HPFP internals, stage 2 CS intake, CP-E TMIC, CS catback with racepipe, GFB hybrid BOV, CS EBCS
mituc
VersaTuner guru
Posts: 1323
Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: Boost Pressure graphing looks strange...

Post by mituc »

You're not logging a lot of useful stuff in this log but most likely if you logged the injector duty cycle you'd have seen a few more things. I'm not sure if you lost traction there or if you hit a load/boost lilmit, because it can be either judging by the WGDC.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
Lolmooses
Posts: 43
Joined: June 16th, 2020, 1:53 pm

Re: Boost Pressure graphing looks strange...

Post by Lolmooses »

Let me add some detail that may or may not be useful. That pull consisted of downshifting from 5th to 3rd and flooring it immediately after since I had someone trying to mess with me on my way to work. I had BCS values adjusted too aggressively on that tune hence the overload. I'm targetting 2.25 at 4500 and in that log it went above 2.3 which is why the wastegate DC spiked down and back up like that I'm assuming. My wastegate DC curves typically looked like the one in the log until I found better values to use through trial and error and adjusted the BCS Correction tables, but even with the wastegate curve looking like that in the past, boost pressure and AFR never did this before. Checking all my limit tables aside from gear load limits, I'm not seeing it hit any limit values in that pull though. I've done several more pulls since then, but have not been able to reproduce what happened.

It's hard to tell about loss of traction being this is a 6, but I can't imagine I'm making enough power to spin the front tires on a straight road before the AWD kicks in. We're talking milliseconds here though, so I could very well be wrong.

Since the ECU works strictly off absolute pressure, is boost pressure just a calculation of (MAP - 14.7) done by VersaTuner for logging purposes? If so, it's really strange that Boost Pressure and MAP don't track each other correctly at all for part of that pull.
2006 MS6: CS HPFP internals, stage 2 CS intake, CP-E TMIC, CS catback with racepipe, GFB hybrid BOV, CS EBCS
Lolmooses
Posts: 43
Joined: June 16th, 2020, 1:53 pm

Re: Boost Pressure graphing looks strange...

Post by Lolmooses »

After some more thinking, I think I figured it out. I use an OBX Bluetooth logger so I'm not driving around with a cable next to my legs. I think the bluetooth latency is causing lag in the log because the -11 psi would make sense when I let off for a split second to blip the throttle to go into third, but it doesn't show that blip in the log. I may just say screw it and buy the VersaTuner logging cable, because this isn't the first time where I felt like the data being logged looks delayed between the different PIDs.

Also looking at logs from last year when the car was basically stock, boost pressure still looks like a wave, so this whole thing is ultimately a non issue that I hadn't noticed before as I was using a tactrix at that point with VersaTuner free, so interface has nothing to do with it looking like a wave.
2006 MS6: CS HPFP internals, stage 2 CS intake, CP-E TMIC, CS catback with racepipe, GFB hybrid BOV, CS EBCS
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