[Diy_efi] Fixed frequency PWM batch mode FI

[Mike]

For what its worth,

My 3L Turbo straight six has a Bosch ECU, hot wire afm, port injection,
factory built in 1986 and has been running really well with Bosch 4-point
spark plugs and runs 10.5psi boost T3 Garrett (factory was 7psi)
on 96 octane unleaded (they call it 'premium' over here) and here
is a typed paste from the factory workshop on this subject:-

I quote from page 6C-5 'VL Series Service Manual Supplement'

"With many early fuel injection systems, fuel was injected into the
inlet port just prior to the beginning of the intake stroke. This is
not the case with the Electronic Combustion Control System (ECCS).
All fuel injectors are electronically to the control unit so they
all inject simultaneously. Therefore fuel injection is made independently
of the engine stroke cycle.
With the ECCS, injection is made once every engine crankshaft revolution,
after the control unit receives information regarding crankshaft position
from the crank angle sensor.
One injection of fuel provides only half the required quantity necessary
for the operation of the 4-stroke cycle of the engine, therefore injection
is made twice during one 4-stroke cycle, ie. Once every engine revolution.
Fuel in this system is not injected directly into the cylinder, but is
injected into the intake ports of the cylinder head. Therefore the air-fuel
mixture is drawn into the cylinder when the intake valve opens. During
strokes, other than intake stroke, the air-fuel mixture is kept
outside the intake valve."

This is one of the better factory manuals by far with lots of nice
graphs, correction factor descriptions etc.

If someone has an ftp site I can send some zipped tiff files to, then
I can take some scans - probably be about 10meg all up, let me know in
next 7 days or so if anyone wants them for the group to access, and no
I won't email them just to one person - so work something out if you
want them - I think they are worth looking at for refernce  :)

rdgs

Mike




At 12:13 PM 21/8/2002 -0700, you wrote:
>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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