Netres availability

[Len Sabatine]

     Ok . Now look at the manifold in relation to the Firing Order.

               Cylinder Order   vs Firing Order  1-3-4-2
               v->>>>>>-v
              4 <-> 3      2       1
                      ^-<<<<< -- 
^
        See the manifold signal bias is Cyls 3 and 4.
     There's need to bias the injectors or do a manifold fix to
     smooth the Fuel distribution. Most likely both, unless
     fuel distribution doesn't matter. I'd focus on the OE
     Inverted Tri Y  inlet shape and why they chose to 1/2
     batch fire with 1 injector, in relation to synch time. GM
     used the easiest method for production.
     Aftermarket wise . a Clifford Intake starts looking better
     all the time , altho that would need tweaking with a 7747
     and 2x injectors as well . IMO.
     Len

>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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