[Diy_efi] Air/Fuel meter now working! And L-jetronic
amdcpu at hot.ee
Thu Jun 16 20:20:00 CDT 2005
> > If we have 50cc exhaust gases in 500cc cylinder, the
> > intake air is 450cc.
> Assuming that none of the air got pushed back out by
> the exhaust gases, and also assuming they are at the
> same pressure (it's pretty much guaranteed they are
> not). Further, the amount of exhaust dilution will
> change the burn rate, which might dictate a change in
> fueling to accomodate it optimally.
If something is pushed back, it restricts also the flow.
> > At the exhaust valve, there is already A-F-mixture
> > not air, if some of the mixture goes to the exhaust,
> > the AFR won't change.
> That's assuming that A) all the fuel is delivered well
> before valve overlap occurs, and B) homogeneity of the
> imcoming mixture is perfect, and does not change based
> on valve opening, exhaust velocity and temperature,
> I can assure you, these things are all important in
> determining how much fuel should be delivered.
Most of todays systems doesn't measure these things.
With this theoretical system, we would also need 1 pot :D
Or just an bunch of oxygen sensors + EGT and ion-sensing :D
It's just simplier=cheaper to tune every model than use hi-tech systems.
I won't buy a car whose sensors cost 1000$/pc
> > Yeah, but i meant to leave the VAF into the
> > atmosphere.
> How could you determine how much air was entering the
> cylinder if you're measuring air entering the plenum?
> If air pressure in the plenum never changed, this
> MIGHT work, but if pressure in the plenum changes
> (especially if it changes quickly, which is common on
> turbo apps), it CAN'T work properly (unless you add a
> plenum air pressure reading somewhere, in which case
> why bother with a VAF?)
I agree, should just use MAP.
But in theory, if plenum pressure changes, it must pump in air if plenum
dimensions are not changing.
I don't know about turbos. Do they have extra plenum before TB too? NA's
have mostly plenum after TB.
Yeah, with turbos it is complicated, since they have "blow-off" too.
We need cylinder pressure sensor and direct injection.
> >>> Although analog ECU's didn't have ROMs, they had
> >>> maps. Mapped by resistors. ;)
> >> That's not a map.
> > And analog computer is not computer?
> > The point is, LE-Jetronic has soldered VE-Table in
> > it.
> It has a rough approximation of a fueling curve
> soldered into it. It's not a VE table, and it's not a
> map, which would imply discrete settings for
> load/speed points. If there was an array of resistors
> that was checked, like you'd find on a digital ECU's
> EPROM, THAT would constitute a map.
Havn't you looked inside l-jetronic, they have many arrays of resistors.
Resistor for "every" condition.
We can call map inside the EPROM also a "rough approximation of a fueling
OK, lets stop this :D
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