Map and Baro Compensation

[Ipe]

MoTeC,

I’m going to use a M84 to control an ITB NA engine. I’m going to tune the engine based on TP but with a MAP comp and connect the MAP sensor to the manifold to have a good map reading for idle control. But this car will be used with a good variation of altitude, over 3,000ft. Is there a way with the M84 to setup a second MAP sensor to make barometric reading and make a table using this input to compensate for altitude variation as Ross from MoTeC suggested on an old post (viewtopic.php?f=39&t=1277 ) with a setup similar to mine.

Ross quote:
“You can tune a NA engine based on TP but with a MAP comp and connect the MAP sensor to the manifold. This normally works well but there are exceptions where a stable MAP reading is difficult to obtain, for example on a multi throttle setup or an engine with a lot of cam overlap (or in the case of a Rotary a lot of "port overlap"). The advantage of tuning this way is that the ECU will respond better to load changes at low or closed throttle and/or if an idle control valve is being used. I would still trigger the accel enrichment from TP but you will find that you do not need as much. This setup will also do a reasonable job of compensating for changes in altitude. You can have a separate baro compensation though if you find that there are changes in mixture that the MAP compensation is not correcting.”

“A separate Baro sensor can be used and is a good idea if the engine is operating at different altitudes. Normally Baro compensation is the standard "double the air double the fuel" formula but if it is used in conjunction with a MAP sensor it can be used to compensate for changes in VE as a function of ambient air pressure. For example if you run an engine at altitude with 80 KPA this will have an effect on the exhaust back pressure which can change the VE even on a turbo engine. In other words if you have a turbo engine running with 1 Bar of boost at sea level the fueling requirements will be different if you run the same engine at 1 Bar of boost at the top of a mountain where the air pressure is lower. The pressure in the intake manifold is the same but the exhaust pressure is not and this affects the efficiency of the engine. On an NA engine this also changes, partly because of the lower air pressure in the intake but it also effectively changes the "tuned length" of your manifolds. A normal MAP sensor can be used for Baro comp. It just needs to be mounted where it is exposed to ambient pressure.”

[Rude Engineering]

You can do this with the M84.

First of all if you are going to use a MAP sensor with an ITB setup you will need to port the MAP sensor to all cylinders so that you get a stable MAP reading. The Input Setup will allow you to change the filter value for the sensor if there is a lot of fluctuations in the reading.

For your Barometric Pressure Sensor you will need to connect this to AV8 and set up the sensor on User 1 (Sensor Setup/Input Setup/Other).

For the Comp Table you will need to enable the Y Axis for Fuel Comp 1. The Y Axis is "User 1". You will need to assign pressure values to the axis.

As you will already have a MAP Sensor the Barometric Pressure Compensation Table will need to be tuned because you are already making part of the compensation with the MAP sensor.

Hope this helps...

Ross