[Diy_efi] Fixed frequency PWM batch mode FI

[Les Dittert]

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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