Nominating a MAF sensor as the Inlet MAP sensor

[RGAClarke]

This might seem a bit weird but my application of an M130 is for a Subaru EJ253 in an aircraft and I will not be able to use the fourth (Ambient Pressure) axis to tune VE to minimum achievable ambient of around 50 kPa in advance.
Relatively small reductions in ambient of 96 to 88 kPa have seen increases in VE of about 7% at higher power so I expect to see substantial changes at normal operating levels around 8500' or 75 kPa.
It occurred to me that it might be possible to specify and calibrate my MAF sensor as the Inlet MAP sensor and this would provide an automatic method of establishing a proper position on the VE (fuel) table.
I attach an image of a log file which shows the close relationship between MAF and MAP although the former has a bit more resolution and is able to pick up on inlet cam adjustment problems. (see first WOT segment).
If anyone has any thoughts on the proposal I should be very grateful for them.
Rupert Clarke

[Calibrated_Dan]

Firstly what version of Firmware are you running?
What is your hardware setup? [i.e. M130 with LTC & E888]

Are you running an Ambient Air Pressure sensor on your setup?
The VE table has Ambient Air Pressure available as an Axis so there's no reason why you couldn't use any data logs you have available to build a suitable map rather than flying and tuning at the same time [which I'd guess would be against at least one aviation regulation ]

Inlet Mass Airflow is calculated within the GP package code based on Inlet Manifold Pressure, Engine Speed and a load of other variables, if you're running the MAF sensor you'd usually see that input setup as the Airbox Mass Flow sensor.

We've got some code that we've run on some BMWs that uses the factory MAF sensor as the main load input for the fuelling and ignition models, but it's not as simple as using an Airflow meter as a MAP input when you're using a VE based fuelling model.

Daniel @ Calibrated Performance

[RGAClarke]

Hi Daniel
Thanks for the reply.
I have an M130 with GPA licence and level 2 logging. Firmware version is 01.07.0003 with build version 1.4.0.148. LTC is LSU version with a single Bosch LSU wideband but I am thinking of adding a second wideband if I can get things worked out with the current ECU.
Thanks also for pointing out that the Inlet Manifold Flow is a calculated value and that I need to look to the airbox to see the real MAF sensor.
The Airbox MAF is not included in the default data logging but I think that I have worked out how to edit data logging channels so that it is, but still do not know how to save my preferences so that the list does not reset every time I turn off the computer. The Airbox MAF is set up as an analogue voltage input with the translation currently a straight line. The Denso 22680AA380 sensor is common to many Subarus including WRX and STi.
I have an ambient MAP sensor which I have been using in flight to generate values but enabling logging of the MAF sensor will be a great help as you suggest.
The reason I would like to go to MAF for load is that I am going to find it very difficult to tune MAP for higher altitudes in advance (up to 24,000' or around 50 kPa) because the engine will need to be functioning at its best to get there and I would also need go to outback Australia for that height to be legal.

[Calibrated_Dan]

With GPA the fuelling model should be able to handle your needs without needing to use the MAF. The MAF's translation will also vary dependant on the state of tune of your engine and if you loose the MAF signal through an air leak then you run the real risk of the engine cutting out or loosing a huge amount of power which would be catastrophic in an airplane. Feel free to datalog the Airbox Mass Flow sensor voltage and you could setup the linerisation against the calculated Inlet Mass Flow as long as you're not under transient conditions.

I'm also unsure about how the altitudes you're going to see will start to affect the Wideband Lambda readings as the pressure in the exhaust system does affect their accuracy [it can be accounted for, but something you need to be aware of]. I'd be inclined to run EGT on your engine to aid running at higher altitude, an E888 would be a great addition as you could run EGT per cylinder which would show up any different running you get across banks and allow you to trim the engine to suit.

I'd be inclined to setup your VE table at various altitudes, say in 15kPA intervals - you can then see if there's a trend curve at a set RPM+MAP that you can extend out to the next point. It will get you close enough that you could then take short flight to the next altitude and check how far you are away [using closed loop as best as you can]. It's how you'll find most calibrators will approach an engine they haven't worked with and have limited information on.

The thing you'll find with change in Ambient Pressure that often gets overlooked is that ignition timing will affected due to the pressure differential helping to scavenge the exhaust gases better at higher altitude [lower Ambient Pressure].

It's certainly an interesting project you've got going but in my opinion you should stick with the standard GPA fuelling model. If the MAP sensor fails and you've got the Warnings setup correctly the system will fall back onto the Estimated MAP signal table and you could at least land the plane, using a MAF if that signal goes then unless the package you move too has a safety backup then you'd be in big trouble.

Daniel @ Calibrated Performance

[RGAClarke]

Thanks again Daniel
The "Automatic" backup feature should the "Inlet Pressure" sensor trigger its diagnostic limitations IS something that I want to retain. I was hoping that by telling the ECU that the MAF sensor was the Inlet MAP, the facility would continue to function.
Other ideas were to fill the VE table boxes with 100s as the VE would be automatic from actual flow. I would need to curtail IAT values to prevent the ECU distorting the fuel too much and I understand that the ECU derives ambient pressure at ignition before cranking so would need to provide a translation which gives a sensible pressure at zero flow.
I actually have aircraft EGT sensors for each cylinder and a Motec EGT sensor via amplifier for cylinder #2.
However, when I sought to enable an alternative fuel aim table for EGT I got into trouble as the Motec sensor reads a bit higher than the aircraft ones (Electronics International) at around 1420 compared to 1330°F at high power settings and the ECU seemed to have trouble dealing with the EGT table impacting the main table. At least that is the impression I got from the oscillations in closed loop which are shown on the attached image of the log file.
I have since disabled all auxiliary fuel aim tables and closed loop is working well.