MAP compensation

[64hardtop]

I have set up an M8 with load axis set to MAP/EMAP. This is a N/A application with fuel reg connected to the manifold and the EMAP to atmosphere.

Is the default MAP compensation still applicable for this configuration or should this be zeroed out?

[DarrenR]

When you set the ECU up this way the Fuel MAP Comp table can be your barometric pressure comp which also has the advantage of flatening your main table giving better tuning resolution. In this case the EMAP comp should be set to all 0.
The other option is to use the EMAP comp as the barometric pressure comp and set the MAP comp to 0, but you lose the advantage gained by using MAP comp for baro.

That might be a little confusing, so if you need more detail let me know.

Regards,

[64hardtop]

Thanks Darren. OK, so lets see if I've got this correct. Using MAP only for load/efficiency with no EMAP configured and having MAP comp set to default, I still have effective BARO compensation? It's just that I've read on another forum where there's a different take on it. The other school of thought is that effective BARO comp can only be achieved by sensing it independent of MAP. My thoughts were that the overall fuel map would be based on MAP with the EMAP (to atmosphere) compensation being a modifier for BARO. Meaning that the MAP comp should be zeroed out otherwise BARO would be getting compensated for twice, if you get what I mean. Thoughts?

[DarrenR]

One thing that can confuse things is if you are using a 'gauge' type sensor that references to atmosphere. This type of sensor will read the same if you are at sea level or high in the mountains. The reading is a pressure, but it is offset by atmospheric pressure. In this case you need a sensor to measure atmospheric pressure and do a compensation based on it since it is not measured otherwise.

Normal MAP sensors are sealed meaning the pressure they measure is referenced to an internal pressure so read a atmospheric pressure change. Using MAP only as the Efficiency point means the atmospheric comp is effectively done in the tuning of the fuel table. The engine doesn't know if the atmos pressure is 70kpa and throttle is wide open, or atmos is 100kpa and the throttle is at 70%, with a manifold pressure of 70kpa for example. Not exactly the same fuelling is required for both but close, the difference being the exhaust back pressure and the amount of difference will depend on the exhaust system.
In this case the if the fuel table is tuned with default the MAP comp in place, it is there only to flatten your main fuel table which effectively increases the resolution of the table. Do you understand how that works?

Where you have a setup like you have with the efficiency point calculated from MAP/EMAP and EMAP is atmos pressure, the efficiency point is effectively a percentage of atmospheric pressure. Now if you don't have any comp for atoms pressure you will have the same fuelling at full throttle for 100kpa or 70kpa atmos pressure and that's not correct.
Having a MAP comp still works since at full throttle the MAP pressure is 70kpa meaning the MAP comp takes out 30% fuel, even tho the main table is still at 100. This can be more accurate than using just MAP since it takes into account the atoms pressure on the exhaust. The air pumping efficiency of the engine will affect what this needs to be.
Using an EMAP comp instead of MAP comp does the same thing, except you don't get the fuel table flattening effect. You could use normal MAP comp and just small values in the EMAP comp to tune the affects of atmospheric pressure change, since trimming the MAP comp will also affect you tune when at a constant atmos pressure.

It is a fairly complicated topic, and is why most people don’t bother using it since it only has a small effect...

Hope that makes sense?

[64hardtop]

I think I have my head around it after reading your response a few times and letting it sink in. MAP comp and having the fuel reg referenced to the manifold looks after the BARO compensation on the intake side of things. How would I go about quantifying the settings in the EMAP table in order to compensate for the BARO effect on the exhaust side of the engine. Measure and log exhaust system pressure against atmo as seen by the EMAP sensor? In order to measure exhaust system pressure, do you have a sensor type/model recommendation and install method? I may be splitting hairs here but since the ecu has the capability, I'd like to evolve the 'perfect tune'.

[DarrenR]

Just to clear something else up, connecting The fuel pressure reg to the manifold isn't there for baro comp. Fuel flow change is not linear to fuel pressure change, where injector opening time is linear, so it is better to change time than pressure.
The manifold pressure comp on the reg is to keep the fuel pressure across the injector the same at all times. If you have 50kPa in the manifold and didn't compensate the fuel pressure, you would have 50kPa more pressure drop across the injector (force making the fuel flow) than with 100kPa manifold pressure. Connecting the fuel reg to compensate for manifold pressure actually removes any baro comp effect.

The only way to tune atmospheric pressure comp correctly is to tune with varying atmos pressures. Not too hard if you can lower the pressure of your dyno cell, otherwise you are left to go for a drive in the mountains and post tuning using the logging. You need to be careful of this, since the air temp is usually a lot cooler in the mountains and if your air temp comp is not already well tuned then you can't be sure if you need to adjust air temp comp or baro comp...
I can't say exactly how accurate our standard comp is, but i have never had a need to adjust it, but my experience with such things is limited.
If you have a fairly free flowing exhaust, the EMAP as atmos pressure would be close enough. For turbo engines this is obviously no good, so the normal thing to do is tap a 1/4" steel line fitting into the collector and coil it around into a normal MAP sensor. While there is no flow, pulsation of the exhaust make the hot gas travel a long way, so the length of the tube it a trade off between removing heat and sensor response. You will need about 1 to 2 meters of tube, sensor response is not as important as removing the heat.
You still don't need to set anything in the EMAP comp, since extra exhaust pressure is compensated for in the main table where MAP/EMAP = Efficiency Point so a higher EMAP = a lower EP and almost always less fuel and if tuned right should be the right amount less?

I am a firm believer of the ‘KISS’ approach, so while we put these features in, using more complicated functions can often turn out worse?

[mr2andy]

I'm sort of asking the same questions on another post and hope you guys don't mind me hijacking this one

Say we are using MAP/EMAP as the fuel map load point. This will basically create percentage 100kPa/100kPa * 100% = 100%.

Scenario 1 (MAP = 120kPa, EMAP = 100kPa <-- atmospheric, RPM = 2500)
Load point will be 120/100 * 100% = 120%
FUEL = X amount

Scenario 2 (MAP = 108kPa, EMAP = 90kPa <-- higher altitude, RPM = 2500)
Load point will be 108/90 * 100% = 120%
FUEL = Y amount

Scenario 3 (MAP = 120kPa, EMAP = 90kPa <-- higher altitude, RPM = 2500)
Load point will be 108/90 * 100% = 133%
FUEL = Z amount

Question 1: I would assume the fuel needed for X is different than the fuel needed for Y that's why the need of MAP compensation?

Question 2: Why would using the MAP compensation table better than using the EMAP Compensation table? What's the calculation different between this two tables? Also, what do you mean by flatening the fuel table and higher resolution when using map comp table.

Question 3: Assuming the map comp table is using the straight "double the pressure, double the fuel" logic.. The fuel needed for Y is less than X?

Scenario 3 besically illustrate that at different altitude with the same map reading, the fuel needed at the same RPM is different.

[DarrenR]

Hi mr2andy,

1. Yes that is correct, MAP is lower and even tho EMAP is also lower by a similar amount, MAP has a much larger affect on the efficiency of the engine than EMAP. It's like with a turbo engine, with 100kPa MAP and 100kPa EMAP (no boost) makes far less power than 200kPa MAP and 200kPa EMAP.

2. Ok so there is no difference in the actual compensation calculation between MAP and EMAP. The reason we prefer MAP comp is only because of the table flattening affect.
Say you have EMAP comp and no MAP comp and the engine is idling at 40kPa MAP, 100kPa EMAP and i need 2mS of fuel for lambda 1.00, so my table is set to 20% (IJPU of 10mS).
Fuel calc is 10mS (IJPU) * 20% (Base fuel) * 100% (EMAP Comp 0% trim) = 2mS

Now switch that around so we use MAP Comp and no EMAP Comp with the same situation the base fuel is 50% -
Fuel calc is 10mS (IJPU) * 50% (base fuel) * 40% (MAP comp -60% trim) = 2mS

Now you may say there is no difference except the table is flatter with higher numbers in the low MAP pressure areas, but the resolution of the base table is 0.1%. If you want to increase the amount of fuel at this point, with EMAP comp you would change the table to 20.1% and the fuel pulse width changes to 2.01mS, a change of 10uS.
Now if you have MAP comp and you add fuel to 50.1% the fuel pulse width changes to 2.004mS, a change of 4uS.
Do you see how MAP comp over EMAP comp has effectively increased the resolution of the table?? This has a much larger effect if you are using numbers in the table around 2 or 3%, sometimes 2.1% is not enough and 2.2% is too much!

3. Yes, same as the answer for Q 1. To elaborate, let’s say for scenario 1 you need a fuel pulse width of 12mS, with MAP comp the base table would be 100%, that’s 10 (IJPU) * 100% (Base Table) * 120% (MAP Comp 20% Trim) = 12mS.
With EMAP Comp it would be 120%, 10 (IJPU) * 120 (Base table) * 100% (EMAP Comp 0% trim) = 12mS

Now scenario 2 with the same load point, with MAP comp the fuel pulse width would be 10.8mS, 10(IJPU) * 100% (base table) * 108% (MAP Comp 8% trim) = 10.8mS.
With EMAP Comp the fuel pumps width is still 10.8mS, 10(IJPU) * 120% (Base Table) * 90% (EMAP Comp -10% trim) = 10.8mS

So it makes no difference to the end result if you use MAP or EMAP comp, just the values in the base table differ.

Cheers,

[mr2andy]

Say you have EMAP comp and no MAP comp and the engine is idling at 40kPa MAP, 100kPa EMAP and i need 2mS of fuel for lambda 1.00, so my table is set to 20% (IJPU of 10mS).
Fuel calc is 10mS (IJPU) * 20% (Base fuel) * 100% (EMAP Comp 0% trim) = 2mS

Now switch that around so we use MAP Comp and no EMAP Comp with the same situation the base fuel is 50% -
Fuel calc is 10mS (IJPU) * 50% (base fuel) * 40% (MAP comp -60% trim) = 2mS

Base on Darren's example above, the result calculation between map comp and emap comp will always be the same, but the way it was calculated between these two methods are different which resulted in the different base fuel map.

Let me try understanding the calculation for map comp again. How did you get the 40%(Map comp - 60% trim)? Is it because the Map reading is 40kPa? A normal Map Comp table is double the air double the fuel setup. In the map comp table.. 100kPa = 100%, 200kPa = 200%. In the above example, 40kPa meaning we only need 40% of the fuel, correct?

I need some suggestion on my current setup. It's a 3SGTE turbo with a 3 bar Map sensor + a 1 bar map sensor which work as a barometric sensor. What is the best fuel table load site selection?

1) Map only as fuel site load point + map comp + emap(which reference the 1 barometric map sensor) comp?
2) Map/Emap(which reference the 1 barometric map sensor) % + Map Comp?

In the v35 software, the Map/Emap % (barometric only) <------------ why is that? I thought Emap were originally meant for Exhaust Map sensor.

Cheers
Andy

[Wolf_Tm250]

Let me try understanding the calculation for map comp again. How did you get the 40%(Map comp - 60% trim)? Is it because the Map reading is 40kPa?

Yes, it is because Map is 40 kPa and Fuel comp is 40 kPa = 40%

A normal Map Comp table is double the air double the fuel setup. In the map comp table.. 100kPa = 100%, 200kPa = 200%. In the above example, 40kPa meaning we only need 40% of the fuel, correct?

It's not because at 40 kPa you'll EXACTLY need 40% of the fuel, but it's always to get a more flatten (and "centered" I understand...) base table and a better resolution.

I need some suggestion on my current setup. It's a 3SGTE turbo with a 3 bar Map sensor + a 1 bar map sensor which work as a barometric sensor. What is the best fuel table load site selection?

1) Map only as fuel site load point + map comp + emap(which reference the 1 barometric map sensor) comp?
2) Map/Emap(which reference the 1 barometric map sensor) % + Map Comp?

Personally:
3) Map only and trash the baro sensor...