[Diy_efi] About MAP sensing and it's jitter

[Tomas Sokorai Sch.]

Right now in my test code, one sample is taken for every cylinder, as my 
timing marks on the crankshaft are 4, 90 deg. apart. That makes 8 signals 
every engine cycle (2 crankshaft rotations). Is it a good idea to still 
lowpass filter them?
It's output now looks almost good to me, considering that my valvetrain has 
some wear.
BTW, I converted the datalog images on my site from PNG to JPEG as it could be 
the problem that prevented you from seeing them.
Can you please explain the part of the "more inter-cycle oscillations when WOT 
or at high RPM" ? Wouldn't the higher air speed flatten the oscilations at 
high RPM?

On Wednesday 14 January 2004 11:15, Alexei Pavlov wrote:
> Hi,
>
> I did not succeed to see you signal images. Even if you got better
> signals afterwards I'd like to see the following:
> The question is: do you want to see real pressure or do you
> want to use average cycle pressure to manage the engine ?
> Probably the second. In this case you need a correct sampling
> of intake pressure oscillations. You must sample at a frequency
> you've choosen and low-pass filter higher frequencies.
> Then the CPU will compute the average pressure of 1 engine cycle.
>
> If you use higher frequency sampling you'll always get unstable
> signal, as cylinders are all different and intake system has its
> proper frequencies.
>
> From my experience with rather high overlap and very low overlap engines
> I'd say you'll get more inter-cycle oscillations when WOT or at high
> RPM.

-- 
Tomas J. Sokorai Sch.
Socio director, Gerente Proyectos Especiales
Xperts Ltda. F: 63 244591, Valdivia, Chile
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