Question on Interpolation

[v8zcar]

This is similar to one of my other questions...but why does the ECU interpolate if there are identical values in a given area at a certain range of time?

What I mean is, in watching my datalog of my idle. I'm getting rich and lean spikes. When I focused my attention on RPM, MAP, Target AF, and Actual AF, I saw that the MAP values in the datalog were fluctuating.

But in the VE table at the exact same range/time (confirmed with overlay), the VE values are all the same in a 6 x 6 cell area. I would expect to see the MAP values for this range/time to be a flat-liner.

The same is seen in my Target AF table, identical values but datalog shows the Target value fluctuating.

Thanks,
Owen

 

[Craig Smith]

The ECU ALWAYS interpolates between cells. If the values of the cells it is reading from are all the same, the interpolation simply has no effect. But, if you were moving from a cell with a value of 50 into a cell with a value of 60, the ECU would "transition" the VE value from 50 to 60 in 16 increments from the center of the first cell to the center of the second one. If both cells were 50, the final VE number would be 50 throughout the transition.

The MAP reading is an input from the MAP sensor, not a calulated value. It will vary depending on what the engine is doing.

If the target a/f value is changing, the ECU is reading from cells of varying values in the target a/f ratio table. No ifs, ands, or buts about it. Nothing other than the value of the cells you are operating in affects the target a/f ratio.

 

[v8zcar]

Ahhh, now I get it!
I love EFI

Owen

 

[Craig Smith]

I find it to be a fun way to work on a car. I hope you do too.

Feel free to post any other questions here should they arise. I'll be happy to do my best to answer them for you.

 

[carbuff]

Hi Craig,

Just to clear it up for me what you said above, let's see if I have this right:

There are 16 distinct interpolation points between adjacent cells on the VE table. Is this in both x (rpm) and y (MAP) directions? Is the interpolation purely linear?

And it's really not quite that simple since you have to do a 2-dimensional interpolation, right? There are many ways to do that...

Thanx!
Bryan