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Battery voltage compensation.

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My current setup is a N/A small block ford. Single butterfly/plenum type manifold, ID 725 injectors, MAP based tune with the FPR referenced to the manifold. Motec M800. I have the battery compensation as a 2D table since the delta P across the injector is constant.

Moving to an ITB manifold so then the tune will be TPS based with baro compensation and the FPR referenced to baro.

My question is, how do I set up the battery comp since there will not be a constant delta P across the injector and no usable MAP value to build a 3D table from?

Can you post a screenshot of your current compensation table?

The current compensation table is 2D using data that came with the injectors. Since the FPR is currently referenced to the manifold, the delta P is constant so using the data plicable to the base fuel pressure. When switching to an ITB manifold and using TPS as load axis with baro compensation, could I build a 3D table using a calculated channel based off TPS and baro? If so......guidance.

Can you post a screenshot of your current compensation table?

I'd say that if the data isn't available from the injector manufacturer for battery compensation at the different pressures across the injector you're going to have to generate this data yourself. You could have the injectors characterised at the different pressures to get this? Running alpha-N on ITB's typically gives a pretty hard to use MAP signal into the ECU at idle, so if this was one of the axis on your compensation table, it'll be jumping all over the place.

Last Alpha-N ITB setup I did also had the injector pressure referenced to atmosphere. I used a 2D battery voltage compensation table, and the varying fuel pressures, and thus flow was integrated into the fuel map. Not ideal, and means any future changes to the fuel system would require a re-tune, but it still gave a great result.

That's exactly my question. I have the characterisation data for the injector, but how to I measure or calculate the delta p across the injector without a usable MAP signal?

Well, you only have half the data you need, so without a MAP signal, you're not going to be able to get a good reference of the pressure across your injector.

Once the engine it up at revs, the MAP signal will smooth out considerably, you could tee all of your runners into a small plenum and take a map signal from there.

Hey Nigel, you can build a balance tube with a connection to each ITB (as Zac alludes to above) to provide a MAP signal to the ECU and from that you can determine the pressure delta across the injector, even if you are using TPS for fuel/ignition scheduling. I actually prefer to still use this on an ITB application to still allow use of the background fuel comp for MAP to take place. I find this evens out the small fluctuations you often see in an ITB application when you're at a certain throttle setting and go up or down a slight rise in the road.

The reality is that most tuners don't bother with a 3D battery comp table and will just use a fixed pressure delta for their values. The tricky bit is that most take MAP to be atmospheric which is fine when you're above about 30-50% throttle, but at idle the vacuum increases the pressure delta and hence the battery comp is incorrect - Right at the point the dead time has the greatest effect.

.....or mount the injectors in the air box upstream of the throttles. Now we begin a whole delta tau fueling discussion for off idle tuning.....:)

There are millions of cars on the road with returnless fuel systems (no vacuum reference for fuel pressure) and just a simple dead time calculation based on battery voltage. They have algorithms that calculate MAP based on throttle position and use that.

Raymond, I think the relevant issue here is that Nigel is using an M800 which isn't able to model the MAP value, hence his line of questioning.

I have not done this myself, but it should work.

If you have a aux output to spare(output will not be connected to anything) you can set up a aux table. Tp / rpm and then set the output value 0-100% to reprecent the manifold pressure. Would require a map sensor connected when setting up.

Then use that aux output% as a axis in the dead time table.

100%= 100kpa map = dead time at base fuel pressure

0%= 0kpa map = dead time for 100kpa higher fuel pressure.

Thanks Andre and Marius. The ITB manifold does have a 'MAP' manifold setup. This is primarily for brake booster/PCV. Let's see if I'm getting this. The FPR would still be referenced to atmosphere, fueling and spark scheduling by TPS/RPM, and data log TPS/RPM vs MAP to build a calculated channel for 3D compensation. PCV would be removed while logging the data to be accurate. Once the data is analysed, build the table, reconnect the PCV.

Fpr to atmosphere.

And I would use a dyno when populating the aux table. It should not take too much time to Work through the cells and fill inn the recorded MAP for that TPS/RPM.

If you start with all the values in in the aux table at 100% for starting and then get the idle and no load cells corrected you should be able to interpolate a good starting point. Before you go to the dyno.

Please keep in mind that there is a logarithmic relationship between MAP and throttle, but the shape varies a little bit with rpm. See example attached, filtered for 2000rpm. Note that this is for an engine with a conventional intake plenum and intake variable valve timing.

Attached Files

The aux table will acount for that. The aux table will work simular to the manifold pressure estimate table in the m1. And will have to be set in the same manner. Driving throug the cells and setting the "pressure" for how ever many setpoints as is needed. TPS and RPM.

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