Forum » EFI Tuning Fundamentals » confused in calculating fuel table

confused in calculating fuel table

EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals

Page 1

hey in the course engine management system tables the third one table resolutin i didn't understand from where the numbers of fuel tables  did we get them usually we use lambda to 1.0 anf afr 14.7 but in the fuel table the numbers 50-60-100 etc i didn't knew how we did calculate them or how to use a specific number any help

Which ECU are you looking at? Different brands have different ways for representing the data.

With the MoTeC M1, the values in the Engine Efficiency table are Volumetric Efficiency based, this means that they are showing how much of the cylinder is filled in comparison to your reference pressure. So if you have a number of 80, and it is ambient pressure referenced, then this means that the cylinder has 80% of the ambient pressure in it. i.e. ambient of 101.325kPa * 0.80 = 81.06kPa in the cylinder. The M1 then calculates the mass of the air in the cylinder based off of this, and then injects the required mass of fuel to meet the lambda aim.

With the Mx00 family of ECU's, these use a millisecond based fuelling table, where the number in the table is a percentage of the injector pulse width that is configured when you setup the Mx00. So if you have a PW of 10ms, and a value of 80 in the table, then the Mx00 is going to inject 10 * 0.80 = 8ms worth of fuel into the cylinder.

There are other compensations going on in the background for injector dead times, temperatures and pressures as well, but this is the basic premise.

thanks a lot can i do it with this way if the number is 80 in a cell and the lambda is 1.07 and the lambda target is 1.0 so the number will be 87 can i use this method ?


No, there is not always a direct relationship between the number in the fuel table and the lambda value., it may be a smaller number needed due to the flow characteristics of the injector used, the manifold pressure and fuel film and other variables.

if the table is ve and the lambda target is for exemple 1.05 for a cell that have a number of 85 and the lambda target is 1.0 i will put 5% so the number is 90 to adjust the lambda to our stochiometric target isn't this the method that i can use because now im totally confused

Regardless of whether the ECU uses a VE based fuel table or an injection time based fuel table, you can apply a simple correction to your fuel table if the measured lambda/AFR isn't your target.

Let's take your example where you have a value of 85 in your fuel table, the measured lambda is 1.05, and you actually want a lambda of 1.00. We can correct this using the equation taught in the body of the course - Correction factor = Measured Lambda / Desired Lambda. In this case the correction factor would be 1.05/1.00 = 1.05 which means we need to multiply the current value in the fuel table by 1.05.

1.05 x 85 = 89.25. This will correct your error and achieve your lambda target of 1.00.