[Diy_efi] Fixed frequency PWM batch mode FI

[Les Dittert]

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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