Netres availability

[rr]

Wow, did I ever miss this one. I see it now. Once the
timing issues are resolved I can see two ways to resolve
the fueling issue.

The first would be to run the injector in async mode
all of the time. Ths will give up to an 80Hz injection
rate. This is a lot higher than the normal sync rate.

The second would be to use both drivers on the one
injector. On a 4cyl there is twice the time duration
between injector events than on an 8cyl. So tie the
left & right injector outputs together to fire the one
injector twice as often. This can easily be done at the
ECM connector as each injector is wired to two ECM pins.

This second method would be a problem if the injector
durations ever overlapped. Lots of current through the 
lonely injector. Would depend upon engine RPM limits
and injector sizing.

I'd try the async method first. 

BobR.




On Tue, 21 Aug 2001 22:29:04 -0400
 Scot Sealander <Sealand at clarityconnect.com> wrote:
> rr wrote:
>  
> > It was mentioned that the problem with a '747 and a
> 4cyl engine
> > with 1 injector: was that the one injector wasn't
> firing often enough.
> 
> Right.  The problem has not changed.
> 
> 
> > That the one injector was firing every other plug
> firing. This was the
> > cause of the backfiring and herky-jerky motion.
> 
> And I believe that is the problem.  We will try to take a
> little closer
> look.
> 
>  
> > When looking at the common TBI V8, the injector firing
> intervals
> > per spark plug firing is the same.
> 
> Yes, an injector gets fired off every time there is a ref
> pulse.
> 
> 
> > Each injector fires every other spark plug firing. The
> V8 then divides the two
> > injectors between two banks of 4 cylinders. Same as 1
> injector on a 4 cylinder engine.
> 
> Right.  
>  
> > This is by the design of the intake manifold. The
> manifold is split
> > with each half feeding 4 cylinders. Each half is feed
> by 1 injector.
> 
> Right.  Keep in mind that each 4 cyl "engine" gets an
> injector firing
> with every ref pulse it creates.
> 
> 
>  
> > No difference in the fuel feed per injector between the
> 4 cylinder
> > and 8 cylinder engine.
> 
> Right, in that an injector gets fired with every ref
> pulse.  In 2 engine
> revolutions, the V8 fires eight times, and an injector
> gets fired 8
> times (4 times for 2 injectors).  In the four cylinder,
> it fires 4
> times, with 4 injector firings.
> 
> The problem in Dan's case, is that in four ref pulses,
> (two revolutions
> of his four cyl), he only gets 2 injector firings,
> because for 2 ref
> pulses, the injector firings are on an alternate, unused
> output.  So he
> only gets 2 injection events, when he needs four.
> 
> Think of it this way:
> 
> 
> V8: (747 ECM)
>                  1      8       4       3       6       5
> 7      
> 2
>             
> Ref pulses       1	1	1	1	1	1	1	1	
> 
> Injector 1       *              *               *
> *      
> 
> Injector 2              *               *               *
> *
> 
> 
> 
> 4 cyl: (165 ECM)
> 
>                	1	3	4	2	
> 
> Ref pulses 	l	l	l	l
> 
> Injector	*	*	*	*
> 
> 
> The "*" represent inj firings, and the "l" is a ref
> pulse.  Notice that
> the 747 ECM fires with every ref pulse, and that the 4
> cyl also fires
> with every ref pulse.  Notice that the two four cyl
> engines that you
> refer to get an injector firing with every ref pulse.
> 
> What Dan is getting:
> 
> 747 ECM:         1      3       4       2 
> 
> Ref pulses       1	1	1	1
> 
> Injector 1       *              *
> 
> 
> Because the second injector output is unused, he is
> missing half the
> fuel.  If he increases the fuel, one cylinder will get a
> lot of fuel,
> and one will get short-changed.  This arrangement suffers
> from poor fuel
> distribution.  In short, don't use a 747 on a 4 cylinder,
> unless you use
> both injector outputs. (And use them correctly.)
> 
> My apologies for the alignment for the timing diagrams.
> I used both
> tabs and spaces, so it may take editing to get it lined
> up like I drew
> it....  
> 
> Scot Sealander
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