# Thread: This may be a stupid question.

1. ## This may be a stupid question.

I just got my copy of EFILive and started messing with it and my question is alot of the tables are RPM or Kpa vs. mm3 per stroke. Obviously I know what RPM & Kpa are but I don't understand where the mm3 per stroke is coming from. On the Main Injector Pulse table you are entering us of PW based upon Fuel Pressure Kpa vs. mm3 per stroke. How is fuel amount based on fuel amount? This also goes for the Timing tables. Am i missing something obvious here? I have alot of experience tuning gas motors specifically speed density. Your base fuel map is RPM vs. MAP and you enter desired VE which calculates fuel flow. I made some changes to my stock tune and whatever I did I caused a surging idle situation so I am trying to figure out what I changed to cause that so I can go in and edit it. Thanks in advance. This is a great product but does require a good amount of knowledge to what is going on in the engine.

2. I wonder the same thing

3. mm3 is the volume of fuel, commonly also known as cubic milimeters. On a diesel power is rather directly related to the volume of fuel injected on each stroke. For any goven power output and fuel pressure there needs to be a injection pulse of a defined length, the more power we want, the longer the pulse. In order to maximize power we need to make sure that the injection pulse starts at the optimal point. If you spend some time you'll probably find that timing is somewhat related to injection pulse length and RPM, at least when we're trying to make power. The rules for quiet idling, low emissions and pilot vs main timing are probably a bit less clear.

Ira

And it's possible that everything I've said is wrong, but I don't think so.

4. Ok, but how do we reference this to the actual operaton of the engine? Is the another table that has fuel pressure, TPS vs. RPM, or something similar? I am trying to figure out if one table references another and so on. Basically what my point is that if I want more fuel at 80-100% throttle from 1800-3200 RPM do I have to log fuel pressure than reference that to the main injection table? I am trying to figure out the correct procedure on how to tune these engines.

5. After I wrote that I sat down with EFILive and a couple of diesel tunes to compare and started asking the same question. If you look at what WaitForMe did on hes "easy 100 HP" tune, you'll find he used table B0720 as if the axis were actually RPM and Boost and the table contained Desired fuel. In my mind that would suddenly have it all make sense. I've sent a long letter to the authors so hopefully they'll have an answer for us.

Ira

6. O.K, here goes.........

B0727 - This table 'looks up' the desired mm3 for the entire throttle and RPM range. The value derived from here are then used as your mm3 reference.

So now that the ECM has got the mm3 value based on the current throttle position and RPM it then looks to table B0720 as an example.
B0720 then uses that previous mm3 value as one of it's axis references, and Fuel Pressure as well.
From here it determines the injector opening time.
So looking at the table in B0720 for say 60mm3 the injector open time at low fuel pressure (20MPa) is about 2500uS at high fuel pressure (160MPa) it is about 700uS, the result is for any fuel pressure it will deliver 60mm3 of fuel.

Think of B0727 as the table that determines the fuel amount (in mm3) and B0720 as the table that converts the mm3 value into actual injector open time.

Problem is the mm3 axis ends at around 100mm3 on the main pulse table, so going higher than that in B0727 seems pointless.
This is why you change the values in B0720 so that like our example above, instead of the ECM opening the injector for 700uS at 160MPa to deliver 60mm3, you could increase that number so the injector stays open for longer even though the ECM only thinks it is delivering 60mm3 of fuel, it might infact be 75mm3 (or higher).

Of course there is also the various multipliers etc but I hope that clears things up a little bit.

Cheers,
Ross

7. Thank you, that was what I was looking for. Also thanks for developing a great project. Now back to tuning.

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