Netres availability

[Scot Sealander]

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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