Individual Cylinder AF Adjust, was: NTK wb-sensor price

[socrace at ameritech.net]

Yes, "same cylinder" variations happen alot less often than "cylinder to 
cylinder" variations, so it seems reasonable they would need a much slower 
loop response to average them out. This seems to track with what I've seen. 
When tuning a single cylinder (actually a pair of cylinders on a v8), I've 
haven't been able to do much better than about .2 percent mixture change 
per second max, with .1 being more realistic. Any faster and the loop 
starts oscillating. Is that about the timing you saw? And while your doing 
this, of course, the main loop can't be any faster either (I think this is 
right?) so things really bog down. Using this method, it takes nearly a 
full minute to move the mixture from the average level to individual level, 
while nothing else changes during that time.
Bob D

At 02:22 AM 2/6/2002 +0100, Axel Rietschin wrote:
>...probably, but I just ask myself, why would you want to do so? Apparently
>there is a lot of cylinder to cylinder variation and no two cycles are the
>same (at least Heywood says so, see Sec. 9.4.2). By trying to be super
>selective you may end up trying to correct for something that already
>happened and will most certainly not happen again in the immediate future,
>one single cylinder apparently being able to randomly jump over a few "AFRs"
>from one cycle to the very next all by itself (for various reasons well
>beyond ECU control, for example the mixture composition in the vicinity of
>the spark). I suggest that you may well end up making things worse by trying
>to adjust the fuelling this way (I actually made some tests, if you are too
>"nervous" in the control loop (lots of P-gain, trying to react as fast as
>possible) it never stabilizes. I got better results (as far as "mixture
>stability" goes) with gentle correction and some filtering to actually
>smooth thing out)
>
>Also knowing the transport time is useful for adjusting datalogged traces
>for example, but it won't help you a lot as far as closed-loop fuelling goes
>(except that the more of it, the more gentle you must be in the correction),
>of am I missing something?
>
>just my 0.02 ?
>Axel

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