[Diy_efi] Fixed frequency PWM batch mode FI

[Bruce]

Even with port it's a dribble deal at idle.
4 Cyl, at 600 RPM.  100 msec/rev.
12.5 msec interval firing strategy.
8 pulses per crank rev.
4 msec ***standard PW***
.5 PW at idle and 8 msec at 6K RPM

Slower injector firing rate, or staged injectors would make this alot
easier.   The .5 PW at idle is hard to do.   Or just use 2 injectors.
bruce




----- Original Message -----
From: "Les Dittert" <lesd at earthlink.net>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, August 21, 2002 3:13 PM
Subject: RE: [Diy_efi] Fixed frequency PWM batch mode FI


> Bruce, I'm using four injectors fairly close to the ports.
> That's why I'm more concerned about fuel starvation in cylinders,
> as opposed to a throttle body setup and where things have a chance to
> even out.
> I keep thinking of the General Motors in batch fire system where
> everything fires at the same time.
> But they're firing upon close valves open valves and valve somewhere in
> between.
> So I'm thinking, doesn't really matter when it fires, if the valves are
> in random positions?
> I'm keeping in mind that this is a crude air cooled Volkswagen engine.
> I just want something better than the hard to synchronize carburetors,
> and something that
> allows me finer mixture control and adjustment ability without changing
> jets!
> Carburetors when using blow through Turbo are really pathetic situation,
> because carburetors don't know how-to richen and under boost when blow
> through happens,
> i.e. they don't understand pressurized air.
> -- Les
>
>
> -----Original Message-----
> From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org] On
> Behalf Of Bruce
> Sent: Monday, August 21, 1995 12:06 PM
> To: diy_efi at diy-efi.org
> Subject: Re: [Diy_efi] Fixed frequency PWM batch mode FI
>
>
>
> Are you going to use 1-2-4 injectors?.
> If more then one, where exactly do you want to place them?. Bruce
>
>
> ----- Original Message -----
> From: "Les Dittert" <lesd at earthlink.net>
> > Mine is also air cooled  Volkswagen, turbocharged.
> > My only concern is having a beat frequency between the engine RPM and
> > the pulse rate.  In thinking about it more I just need to guarantee
> > the pulse rate is higher than the RPM. I want to use a small
> > microcontroller for this engine.  While it is possible to control the
> > rate of the PWM, it would then
> > perhaps require a crank sensor which is added complexity.
> > I figured since some General Motors engines do batch fire of all
> > injectors
> > simultaneously, they would run into the same problems of uneven fuel
> > distribution
> > if I'm not mistaken.  The other limitation might be getting low enough
> > fuel rate
> > for idle, because of multiple injections happening with very short
> pulse
> > width.
> > I want to keep the system very simple, so I am using a mass airflow
> > sensor to
> > avoid having fancy multidimensional lookups. A couple of lookup tables
> > should do it.
> > I'm not delegating a mission to this either. I'm using a crane hi 6
> with
> > boost retard
> > and that should work fine for this simple engine. Anything is better
> > than the two carburetors that are on there now!
> >
> > -Les
> > -----Original Message-----
> > From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org] On
> > Behalf Of Bruce
> > Sent: Sunday, August 20, 1995 5:26 AM
> > To: diy_efi at diy-efi.org
> > Subject: Re: [Diy_efi] Fixed frequency PWM batch mode FI
> >
> >
> >
> > There was a VW guy that did an ecm that way.  I think he was firing
> > them every 12.5msec. For racing/off road why not?.
> > So long as it's clean enough to idle, who cares?.   I think the other
> > guy
> > took some heat about it not being able to work, but he said it did.
> > Some GMs default to that under some conditions Bruce
> >
> >
> > ----- Original Message -----
> > From: "Les Dittert" <lesd at earthlink.net>
> > To: <diy_efi at diy-efi.org>
> > Sent: Monday, August 19, 2002 8:42 PM
> > Subject: [Diy_efi] Fixed frequency PWM batch mode FI
> >
> >
> > > I have searched high and low and haven't found the answer to this
> > > question:
> > > are there any disadvantages to running the injectors at a fixed
> > > frequency of injection that isn't related to RPM? I realize that
> doing
> >
> > > this in batch mode will result in some injections hitting a close
> > > valve sometimes and then sometimes hitting an open valve.
> > > Since some OEM fuel systems run batch mode where they fire all
> > injectors
> > > at the same time
> > > I figured they have the same situation anyway.
> > > Another question:
> > > If using a fixed frequency you what should that frequency be? I'm
> > > assuming it should be something equivalent to running a sequential
> > > injection system at about 4000 RPM.
> > >
> > > -Les
>
>
>
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