Individual Cylinder AF Adjust

[bcroe at juno.com]

I would think individual cylinder control would be good
for optimizing a smooth idle.

Bruce Roe

On Wed, 6 Feb 2002 02:22:12 +0100 "Axel Rietschin"
<Axel_Rietschin at CompuServe.com> writes:
> ----- Original Message -----
> From: "Lasse Langwadt Christensen" <langwadt at ieee.org>
> To: <diy_efi at diy-efi.org>
> Sent: Tuesday, February 05, 2002 22:03
> Subject: Re: Individual Cylinder AF Adjust, was: NTK wb-sensor price
> 
> > maybe I'm missing something but wouldn't measuring the "gas 
> transport
> > time"
> > be as simple as running the engine, skip one injection event and 
> measure
> > how long it takes before the sensor shows lean?
> > repeat for different rpms, cylinder, etc.
> 
> ...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?
> Axel

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