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

[Marc Reibel]

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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Hi,

thank you guys for your thoughts on measuring exhaust transport times. 
I asked this question, because I've got a setup of two DCOE 
double-barrel weber-carbs on my car. Jetting this little beasts is 
not an easy task, especially without the ability to measure AF-
ratio for EACH cylinder. 
Lasse mentioned the way suitable for injected cars.
On my carburetors, I am only able to change AF-ratio per cylinder by 
changing the jets (not a good idea while the engine is running :),
by adjusting the idle-mixture-screw (not my favourite option)
or to apply some propane into to one cylinders intake port, I'm 
interested in. 
Now comes your point Axel, measuring cylinder individual AF-ratio
for closed loop fuelling is far too complex.
Also, with the mentioned Bandwidth of approx 50 Hz we only have the 
following options to measure cylinder-individual AF ratios :
- 1500 RPM with one wb-sensor measuring all 4 cylinders 
- 3000 RPM with two sensors, each measuring one cylinder-pair with 
  180 degrees between both TDCs
- full RPM range with 4 sensors, one for each cylinder
(all values calculated for an inline 4 engine)

Option #1 would be enought for idle-testing.
Option #2 wouldn't give me far more results than option 1 but
at twice the price :(
Option #3 is the best one. Full range readings, but at astronomical
costs.

So I'll take option #1.

Thanx a lot,

Marc  
 
-- 
Marc Reibel                    
Email   : marc at reibel-web.de, reibel at rhrk.uni-kl.de
ICQ-UIN : 42168505                Nick        : HMX

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