Initial Map Reading for Baro Correction implementation.

[lagos]

I have a DIYPNP unit with a standard map sensor and no separate barometer, and I am using the typical Initial Map Reading option for barometric correction.
From what I understand, the ecu looks at the map reading at initial power on, and sets that as the new zero value that is stored until the next power cycle.

This is a great idea, but what about situations where the engine is restarted after being a full operating temperature, but the ecu is NOT power cycled? Since pressure and temperature are related, and the correction is only checked on power on (and a cold engine), wouldn't restarting the hot engine without a power cycle throw that reading off?

I believe I experienced something like this. The other day I puled into a gas station and turned off the hot engine but did not power cycle the ecu. After restarting the engine, my afr was extremely rich. I drove like this for about a mile until I decided to pull over to capture a log. As you can see in the log, there is a lot of barometric correction going on. I then power cycled the ecu, and you can see the barometric correction and the AFR was back to normal.

So what I'm asking is, shouldn't the firmware set the initial map reading to zero every time there is no rpm, and not just on initial start up to avoid issues like this?

Here is a log of the difference in barometric correction and afr before/after the power cycle.

GairProblem.msl

[jsmcortina]

Surely your ECU is turned off when you turn off the engine?

Barometer is impacted by the weather and altitude, not ambient temperature.

James

[lagos]

Surely your ECU is turned off when you turn off the engine?

Not exactly... I tend to turn the key off, and back on fairly quickly when I want the engine turned off but my accessories to stay on. The ecu doesn't see this type of behavior as a power cycle. I'm sure I'm not the only person who does this.

Barometer is impacted by the weather and altitude, not ambient temperature.

But the initial map reading is not measuring a barometer, its measuring a pressure sensor. My pressure sensor does not have a barometer. Turning off the engine in the manner I mentioned sometimes shows a pressure reading for +2 psi with the engine off due to the increase in temperature.

[kjones6039]

I tend to turn the key off, and back on fairly quickly when I want the engine turned off but my accessories to stay on.

Just guessing here mind you..... but I'm guessing that you have a big electrolytic cap somewhere in the power supply circuit..... maybe for noise suppression.... Am I close?

Ken

[Sam280Z]

A baraometer is just a pressure sensor. The only way for temperature to affect a pressure reading is if the volume is fixed, i.e sealed. Your engine is not sealed. You are seeing something else affecting the fueling.

[lagos]

A baraometer is just a pressure sensor. The only way for temperature to affect a pressure reading is if the volume is fixed, i.e sealed. Your engine is not sealed. You are seeing something else affecting the fueling.

Take a look at the log. At first baro correction is at 104 throwing off the fuel mixture from its target, and right after a power cycle its at 100 and the fueling is correct.

[lagos]

I tend to turn the key off, and back on fairly quickly when I want the engine turned off but my accessories to stay on.

Just guessing here mind you..... but I'm guessing that you have a big electrolytic cap somewhere in the power supply circuit..... Am I close?

Ken

Not at all. I just turn the key off and back on. Tunerstudio stays connected and doesn't show a power cycle. Nothing aftermarket is being used.

[kjones6039]

Not at all. I just turn the key off and back on. Tunerstudio stays connected and doesn't show a power cycle. Nothing aftermarket is being used.

d*** you're quick! You'd make a good card dealer down in Vegas!

Seriously, I'm wondering exactly how you are powering the MS. This is not typical (IMO) no matter how quickly you cut and restore the power. Are MS, injectors and ignition all powered from the same source (relay)?

Ken

EDIT: Just curious..... Why is keeping the accessories powered on that quickly, a priority?

[lagos]

Not at all. I just turn the key off and back on. Tunerstudio stays connected and doesn't show a power cycle. Nothing aftermarket is being used.

d*** you're quick! You'd make a good card dealer down in Vegas!

Seriously, I'm wondering exactly how you are powering the MS. This is not typical (IMO) no matter how quickly you cut and restore the power. Are MS, injectors and ignition all powered from the same source (relay)?

Ken

EDIT: Just curious..... Why is keeping the accessories powered on that quickly, a priority?

Its all powered from the factory toyota efi circuit. Im really not doing anything special here, and im sure if you tried it, you'd notice that you tuner studio will stay connected as well.

Anyway, this is all kind of irrelevant. Whats important is that there is a use case here where just capturing the map sensor on start up might not be sufficient. The log shows a baro correction factor that is not correct, that is then corrected with a full power cycle. I believe this could be fixed with an if statement that sets the inital baro reading to zero when the engine rpm is also zero, and not just at first start up.

[Sam280Z]

How are you getting a baro correction of 104% in the first place? Your MAP just prior to the retsart is right at 100 kPa. Did you start your trip at a higher elevation? To get the 4% additional fuel with the default baro curve you would have had to start the trip at around 80 kPa. Is your baro correction curve tuned? Aren't you having problems with the battery voltage reading too? Could this be related? Can you post your msq?

[lagos]

How are you getting a baro correction of 104% in the first place? Your MAP just prior to the retsart is right at 100 kPa. Did you start your trip at a higher elevation? To get the 4% additional fuel with the default baro curve you would have had to start the trip at around 80 kPa. Is your baro correction curve tuned? Aren't you having problems with the battery voltage reading too? Could this be related? Can you post your msq?

All good questions.
There was no elevation change. This was all local driving on flat roads for a distance of just a few miles. AFR was perfect, then I pulled into a gas station, turned the engine off but not the ecu, turned the car back on and noticed the gair was much higher than it should have been.

As for the battery voltage issue, I'm hoping the bad transistor that I removed was the cause of the problem. So far as you can tell in the log, the battery voltage has been fine.

Baro correction is all set at zero.

Here is the msq...

3sgteDIYPNP.msq

[Jdmfreak]

That's odd I have a turbo timer and when I turn the key off my ecu showes a power cycle even though my engine doesn't die
Because power wasn't cut long enough to kill the engine

[Manu]

@James :

I know some OEM that read baro at power on AND each time WOT is reached. This for naturally aspired motor and speed/density algorithm.

Best regards,
Manu