2 GM TBI units, one ECM

[andy quaas]

Well it sounds to me like this 749 ecm is the way to go.  All the
tools are there to make it work on syty.org.  I'm gonna get one this
weekend.

Andy


---Fran and Bud <quest100 at gte.net> wrote:
>
> Andy,
> These TBI's are called "Crossfire", "Model 400's" or "Two by One". 
(Only
> two injectors total)
> 
> The system uses a pair of single injector TBI assemblies mounted on a
> removable manifold cover plate.
> Pass side TBI feeds Drivr. side cylinders, and Drivr. side TBI feeds
Pass.
> side cylinders. hence Crossfire. The Pass. side TBI is biased
forward of the
> center while the Drivr. side is biased rearward.  They are connected
> together by a throttle linkage assy, that can be disassembled from
the front
> TBI but is permanent on the rear TBI.  
> 
> Only the rear TBI has a TPS, but both have an IAC. The front TBI has
a fuel
> accumulator assy where the rear TBI has a fuel pressure regulator.
(possibly
> why the throttle linkage is permanent on the rear - preclude switching
> positions). The fuel is fed to the front unit and then what is
normally the
> return directs fuel to the inlet of the rear unit.  Front and rear
units see
> different pressure profiles and therefore the injectors are calibrated
> differently and should not be interchanged.
> 
> Does anyone know if these injectors fire synchronized or non
synchronized?? 
> 
> One significant feature of this system is a thin plate mounted under
each
> throttle bore as it exits into the manifold.  The plates are
configured to
> cause the air/fuel charge to swirl. This was required to help with
mixture
> distribution because the TBI bore was located near the center two of 4
> intake runners that were lined up in a row and the incoming charge
had to
> change directions from forward to rearward as the firing order
progressed.
> 
> The application for these systems was EARLY 80's.  I dont know what
ECM they
> used or what method of IAC ( stepper/pintle like now or the old
external
> that worked on the throttle linkage) or what algorithm was used
since both
> TBI's had IAC's but each should have let in only enough extra air to
feed
> its own side of the engine.
> 
> Maybe someone out there has some data on the control logic of this
system. 
> ECM/PROM/CalPak or whatever. 
> 
> And what about two dual throttle bodies, as on a tunnel ram?  What
ECM and
> what logic?
> 
> Bud   
> ----------
> ----------
> >From: andy quaas <realsquash at yahoo.com>
> >To: diy_efi at efi332.eng.ohio-state.edu
> >Subject: Re: 2 GM TBI units, one ECM
> >Date: Mon, Dec 7, 1998, 9:11 PM
> >
> 
> >Excuse the ingnorance, but what is a cross-fire system, exactly?  Did
> >this come with a 747?  How are your injectors wired?  Parallel?  My
> >only big question is whether a 747 will be ok with 4 injectors!
> >
> >Andy Q
> >
> >---Bruce Plecan <nacelp at bright.net> wrote:
> >>
> >> 
> >> -----Original Message-----
> >> From: andy quaas <realsquash at yahoo.com>
> >> To: diy efi <diy_efi at efi332.eng.ohio-state.edu>
> >> Date: Monday, December 07, 1998 2:10 PM
> >> Subject: 2 GM TBI units, one ECM
> >> 
> >> 
> >> >I searched the archives and I am left with some questions.  On the
> >> >corvette cross-fire injection, what ECM is used? 
> >> 
> >> I wouldn't think about that ecm, use a 7747.   I've been running a 
> >> Cross fire of the 747 for years.
> >> 
> >>  How are the IAC(s)
> >> >done? 
> >> 
> >> Just wire em in parrarel.
> >> 
> >>  What is the big difference between a 8747 and 7747?
> >> 
> >> 8747 uses a MAT sensor, as I recall.
> >> 
> >>   I know the
> >> >older big-block's came with 90 lb/hr injectors, so does the 8747
have
> >> >larger inj. drivers?
> >> 
> >> Nope, all the TBI's that I know of use the same style P+H..
> >> Bruce
> >>   Thanks.
> >> >
> >> >Andy 
> >> >
> >> >
> >> >
> >> >
> >> >_________________________________________________________
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> >> 
> >> 
> >
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> 

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