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Help with building your Speeduino, installing it, getting it to run etc.
By cbuffhm
#52006
Hello all,

I have a 1994 1.8l turbo Miata that is running on a SpeedyEFI plug and play ecu. I have run into a weird issue regarding a difference in readings between MAP (kpa) and Boost PSI. My car had started running lean at peak boost and when taking some data logs I saw a weird difference between MAP and Boost where the Boost psi read much higher than the MAP (kpa) reading:
Psi vs MAP.PNG
Psi vs MAP.PNG (10.87 KiB) Viewed 770 times

As I understand it, 100kpa is roughly atmospheric pressure and anything above that is would be considered "Boost" pressure. So, according to this log I would have 74 kpa (174 kpa MAP - 100 kpa atmospheric pressure) of "Boost" pressure which is ~ 10.7 PSI when converted. I am more inclined to trust the MAP (the 10.7 PSI) reading since that is approximately what my wastegate is set at.

But, if somehow the Boost PSI reading is correct, that could explain the leaning out issue. The car could be making 15.5 PSI and if the MAP reading is low, then it would not be using the correct cell in the VE table. However, since both pressure readings come from the same source, I don't think this theory is correct.

Nothing has changed for me firmware wise, or hardware wise since I had a normal reading (MAP kpa reading = Boost PSI reading). Is this a Tuner Studio issue/setting? Or could something within my ECU have gone bad? The boost gauge I have on my tuner studio dashboard was showing the 15.5 PSI in boost as well. I am going to go over the line that runes from the intake manifold and the ecu itself but any input would be greatly appreciated. Data log and tune attached.
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#52008
moonie223 wrote:
Sat Jul 24, 2021 9:42 pm
Boost = MAP - BARO

Your Baro is 67kpa for the entire log. This is probably borked. You probably need to look into "use initial map" reading.

174kpa - 67kpa = 107kpa = 15.5psi
That makes a lot of sense and also lines up with the testing I just did.

I plugged in the ecu to my laptop, took the MAP line off the intake manifold so it was open to atmosphere and keyed the car to the "On" position. I put a gauge showing MAP kpa on my Tuner Studio dashboard and that read at 98 kpa while the boost gauge I have in Tuner Studio read at 4 PSI. I sucked on the MAP line and got the boost gauge to read 0 PSI and when it did, the MAP gauge read ~68 kpa.

This makes perfect sense with what you said! I did not notice the low Baro reading in the data log so your comment helped put me on track to perform this test and discover this.

Now, to find the solution. You mentioned the "use initial map" reading setting. Would that happen to be this setting called "Use Legacy MAP reading":
Use legacy MAP reading.PNG
Use legacy MAP reading.PNG (52.34 KiB) Viewed 753 times

Or is that something else entirely?
#52009
Are you bump starting the car or something? You shouldn't be seeing a 68kpa map reading before starting otherwise. I would have thought it grabbed the MAP value as BARO before it sees any RPM, but that doesn't seem to be the case. You should be seeing 98kpa as baro, the boost gauge should read zero just sitting not running.

I think speeduino always uses "initial map reading" as the static baro value when you have no external baro sensor. Doesn't appear to be a way to turn this off.
#52012
moonie223 wrote:
Sat Jul 24, 2021 10:37 pm
Are you bump starting the car or something? You shouldn't be seeing a 68kpa map reading before starting otherwise. I would have thought it grabbed the MAP value as BARO before it sees any RPM, but that doesn't seem to be the case. You should be seeing 98kpa as baro, the boost gauge should read zero just sitting not running.

I think speeduino always uses "initial map reading" as the static baro value when you have no external baro sensor. Doesn't appear to be a way to turn this off.
The car starts, runs, and drives just like normal, other than the leaning out at peak boost which I pretty much tuned away. I started the car and let it warm up for a little bit and and then shut it off and keyed it to the "On" position. These are the readings I got:
Dash with 98 kpa and weird barro.PNG
Dash with 98 kpa and weird barro.PNG (147.25 KiB) Viewed 741 times

You can see that the engine MAP is 98 kpa, Baro pressure is 67 kpa and Boost PSI is 4 PSI. So, from this we can discern that engine MAP is reading fine (98 kpa) and this is how and why the car is running pretty much just fine. The issue is, the barometric pressure reading is way off (67 kpa) thus when the Boost PSI is being calculated (Boost = MAP - Baro) it is doing: 174 kpa - 67 kpa = 107 kpa (15.5 psi) rather than 174 kpa - 100 kpa = 74 kpa (10.7 psi).

This issue doesn't seem to be hurting the cars performance, but could it be the reason for the leaning out in peak boost?
#52013
theonewithin wrote:
Sat Jul 24, 2021 11:29 pm
Correct. No way to disable the baro reading at KOEO.


I would try power cycling ECU but don't att not to start and see if baro works then.

If not do an EEPROM clear and load your tune back in.

I am not in front of the car right now but I will give that a shot later tonight. How might something like this happen? It seems like the baro reading froze somehow after receiving a bad reading.
#52014
You've got baro correction set to a flat 100%, so I don't think it affects anything other than the boost PSI readout. It should still be pulling from the "10 psi"/170kpa rows in your fuel/spark tables.

It seems there's a bug of some kind though, hardware or software, so it's hard to say what is actually going to happen.
#52015
Ah that is correct, I had not really messed with Baro correction in my tune since the elevation is pretty stable where I live.

It is something that I would like to fix however because who know what else could be affected by the possible bug or hardware issue. I don't really like the idea of not knowing what is going on or could happen when it comes to the health of my engine :?

I will update later tonight when I power cycle the ECU and clear the EEPROM.

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