2 GM TBI units, one ECM

[Fran and Bud]

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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